The characteristic zigzag pattern Picture: Kelly Oten, NC State University.
Guest blog by Kelly Oten, NC State University
The elm zigzag sawfly [EZS; Aproceros leucopoda Takeuchi (Hymenoptera: Argidae)] is the newest invasive forest insect detected in the eastern US. The colloquially-used common name, currently going through the ESA common name approval process, is not only catchy, but perfectly describes this defoliator’s unique feeding damage. As EZS feeds on elm leaves, it weaves a zigzag pattern from the margin of the leaf towards the mid-vein.
An Expansive — and Quickly Growing – Range
Native to East Asia, the first confirmation of EZS in North America occurred in August 2020 in Québec, Canada when an iNaturalist user posted a photo showing the characteristic zigzag defoliation. The observer realized it was potentially EZS and emailed local entomologists in the province who visited the site, collected specimens, and obtained species confirmation through the Canadian Food Inspection Agency Entomology Lab (Martel et al. 2021). However, this detection was not actually the beginning.
Three months before the Canadian detection, the same defoliation pattern was observed in Frederick County, Virginia, USA. Observers suspected EZS, but no specimens were recovered and therefore identification could not be confirmed. A year later, the site was revisited and this time, bingo—specimens were present and confirmed as EZS. Subsequent surveys that summer led to detections in eight additional Virginia counties. At the same time, the telltale defoliation was observed in Lehigh County, Pennsylvania, USA, but no specimen could be recovered for confirmation. In 2022, EZS popped up more widely; four additional states confirmed EZS: Pennsylvania, North Carolina, Maryland, and New York.
map created by Kelly Oten, NCSU
Though new to North America, this insect has a history of invasiveness. First detected in Europe in 2003, it now occupies areas from the United Kingdom and France in the west, to Russia and Kazakhstan in the east (Ashikbayev et al. 2018, iNaturalist 2022).
The strange and unusual biology of elm zigzag sawfly
Like all Hymenopterans, EZS goes through four life stages: egg, larva, pupa, adult. Eggs are laid along leaf margins; after hatching, larvae feed on leaf foliage in a zigzag pattern towards the mid-vein. Older larvae consume the leaf more entirely, leaving behind the mid-vein and thicker lateral veins only. Before pupating, larvae spin a cocoon within which they pupate. Cocoons are seasonally dimorphic; summer pupae (which emerge as adults in 4-7 days) are net-like and attached to leaves or twigs. Overwintering pupae are solid-walled and found in leaf litter or soil. Interestingly, overwintering pupae are not just produced from the last generation of the year. Even early in the summer, overwintering pupae may develop alongside summer pupae. Adults are able to begin oviposition immediately; not only do they not need to feed, but they don’t need to find a mate either! EZS is parthenogenetic, meaning they reproduce without mating. In fact, no male EZS has ever been recorded and it’s believed the species is entirely female.
As elm zigzag sawfly larvae (bottom left on leaf) grow, they feed more wholly on elm leaves. Picture: Kelly Oten, NCSU
The entirety of this life cycle can last ~20-36 days when not overwintering. However, the voltinism of this pest is highly variable. Papp et al. (2018) recorded up to seven generations in a year on lab-reared colonies, but in nature in Europe, anywhere between two and six generations has been recorded (Blank et al. 2010, Mol and Vonk 2015). In Virginia, two generations were recorded in 2021 and 1 in 2022. It is unknown what factors play into the number of generations per year, but it’s clear that it’s highly variable. The ability of EZS to multiply rapidly and have multiple generations per year suggest large populations can build in a relatively short time. In fact, this was observed in North Carolina in 2022 and in Europe several times before. Large populations are capable of severe defoliation and may cause long-term impacts on tree health.
This collective life cycle description is based on Blank et al. 2010, Martel et al. 2021, Martynov and Nikulina 2017, and Wu 2006.
Spread
EZS has astonished many with how it seems to be popping up all over the place in such a short amount of time. Since 2020, it has been detected in five US states and at several sites along the St. Laurence River in the Canadian province. The adults are strong fliers, capable of spreading 45-90 km (~27-55 mi) per year (Blank et al. 2014). Given the fact they’re parthenogenetic, relatively small numbers can disperse to begin new populations. Of perhaps greater concern is the potential for long-range dispersal. In heavy infestations in North Carolina, cocoons were found not just attached to leaves and stems, but also non-living objects, suggesting a possible mechanism of long-range dispersal should they become attached to vehicles or other objects transported long distances. In addition, EZS damage ranges from minor to severe defoliation. When populations are low and feeding is minor, it’s less likely to be detected unless intentional surveys are conducted. This cryptic nature might suggest it’s in more places than we are currently aware.
An elm zigzag sawfly cocoon attached to a fence post. Picture: Kelly Oten, NCSU
So, what’s the big deal?
In short, we don’t know yet. Generally speaking, defoliation by insects causes little long-term harm to tree health but severe and/or repeated defoliation can weaken or sometimes kill a host. In Europe, trees severely defoliated by EZS are typically able to re-leaf but may suffer branch dieback and/or reduced growth (Blank et al. 2010, Zandigiacomo et al. 2011). Also of note, EZS is attacking elm, an already-threatened tree due to widespread mortality cause by Dutch elm disease in the 1900s. Defoliation by EZS could further weaken infected trees or, at the very least, present an additional threat for remaining elms (Blank et al. 2010). While it seems aesthetic damage will be the primary concern with EZS, the potential for long-term tree health impactsin the US is uncertain and should be investigated. For now, anyone that finds EZS or its characteristic defoliation pattern are encouraged to report it to their respective state agriculture or forestry agency.
A row of winged elm (Ulmus alata) in NC were severely defoliated by elm zigzag sawfly. Picture: Kelly Oten, NCSU
[See Faith’s earlier blog about the zigzag sawfly here.]
References
Ashikbayev, N. Z., N. S. Mukhamadiyev, G. Z. Mengdibayeva, M. B. Temirzhanov, and N. K. Kuanyshbaev. 2018. Development of forest entomology in Kazakhstan, pp. 42–47. In T. I. Espolov, K. M. Tireuov, E. I. Islamov, S. B. Baizakov, K. T. Abayeva, E. Z. Kentbaev, and B. A. Kentbaeva (eds.), Actual problems of sustainable development in forestry complex, vol. 2. Aitumar Publishing, Almaty, Kazakhstan.
Blank, S. M., H. Hara, J. Mikulás, G. Csóka, C. Ciornei, R. Constantineanu, I. Constantineanu, L. Roller, E. Altenhofer, T. Huflejt, and G. Vétek. 2010. Aprocerosleucopoda (Hymenoptera, Argidae): an East Asian pest of elms (Ulmus spp.) invading Europe. Eur. J. Entomol. 107: 357–367.
Blank, S. M., T. Köhler, T. Pfannenstill, N. Neuenfeldt, B. Zimmer, E. Jansen, A. Taeger, A.D. Liston. 2014. Zig-zagging across Central Europe: recent range extension, dispersal seed and larval hosts of Aprocerosleucopoda (Hymenoptera, Argidae) in Germany. J. Hymenopt. Res. 41: 57-74.
iNaturalist. Available from https://www.inaturalist.org. Accessed August 2022.
Martel, V., O. Morin, S. Monckton, C. Eiseman, C. Béliveau, M. Cusson, and S. Blank. 2021. Elm zigzag sawfly, Aproceros leucopoda (Hymenoptera: Argidae), recorded for the first time in North America through community science. Can. Entomol. 154: E1.
Martynoz, V. V., and T. V. Nikulina. 2017. Population surge of zigzag elm sawfly (Aproceros leucopoda (Takeuchi, 1939): Hymenoptera: Argidae) in the Northern Ciz-Azov Region. Russ. J. Biol. Invasions 8: 25-34.
Mol, A. W. M., and D. H. Vonk. 2015. De iepenzigzagbladwesp Aproceros leucopoda (Hymenoptera: Argidae), een invasieve exoot in Nederland. Entomol. Ber. 75: 50-63.
Papp, V., M. Ladányi, and G. Vétek. 2018. Temperature-dependent development of Aproceros leucopoda (Hymenoptera: Argidae), an invasive pest of elms in Europe. J. Appl. Entomol. 142: 589-597.
Wu, X. Y. 2006. Studies on the biology and control of Aproceros leucopoda. Plant Prot. 32: 98-100.
Zandigiacomo, P., E. Cargnus, and A. Villani. 2011. First record of the invasive sawfly Aproceros leucopoda infesting elms in Italy. Bull. Insectology 64: 145-149.
spotted lanternfly; photo by Stephen Ausmus, USDA; establishment facilitated by extent of invasion by its preferred host, Ailanthus
Seven coauthors (full citation at end of blog) compared various factors associated with numbers of invasive insect species in 44 land areas.These ranged from small oceanic islands to entire continents in different world regions, Liebhold et al. determined that the numbers of established non-native insect species are primarily driven by diversity of plants, including both native and non-indigenous. Other factors, e.g., land area, latitude, climate, and insularity, strongly affect plant diversity. Through this mechanism these factors affect insect diversity as a secondary impact.
Seven coauthors (full citation at end of blog) compared various factors associated with numbers of invasive insect species in 44 land areas.These ranged from small oceanic islands to entire continents in different world regions, Liebhold et al. determined that the numbers of established non-native insect species are primarily driven by diversity of plants, including both native and non-indigenous. Other factors, e.g., land area, latitude, climate, and insularity, strongly affect plant diversity. Through this mechanism these factors affect insect diversity as a secondary impact.
At large spatial scales [greater than 10 km2], regions supporting more diverse plant communities offer greater opportunities for herbivore colonization. Thus, plant diversity promotes invasion through the “facilitation effect”. Since most insects – including most of those introduced to naïve ecosystems – are herbivores, a greater number of possible foods is a clear advantage. Those insects that prey on herbivores benefit by plant diversity indirectly.
Non-native coral tree, Erythrina, in Hawai`i; photo by Forrest and Kim Starr; did wide planting of exotic Erythrina facilitate invasion by Erythrina gall wasp?
At smaller spatial scales, plant diversity might impair the ability of insects to locate hosts because of the “dilution effect”. I have been asking for decades why so few of the Eurasian insects established in eastern North America have not also established along the Pacific coast from Oregon into British Columbia. The region has a plant-friendly climate and almost every plant species from temperate climates is grown there in cultivation. Perhaps the non-native plants – while numerous enough to become invaders themselves – are still sufficiently scarce or dispersed to impair introduced insects’ locating an familiar host?
According to the Smithsonian Institution, Hawai`i has approximately 2,499 taxa of flowering plants and 222 taxa of ferns and related groups. The native flora of the United States includes about 17,000 species of vascular plants; at least 3,800 non-native species of vascular plants are recorded as established outside cultivation. I don’t know how many non-native plant species are in cultivation.
horticultural viburnum invading riparian forest in Fairfax County, VA. photo by F.T. Campbell; did the widespread presence of many non-native viburnum species facilitate establishment of the viburnum leaf beetle?
I note that this article appeared more than four years ago. However, its important findings do not appear to have been integrated into either policy formulation governing plant introductions or pest risk analysis applied to insects or pathogens that might be introduced. (Indeed, we probably need a separate analysis of whether fungi, oomycetes, nematodes, and other pathogens show the same association with plant diversity in the receiving environment.)
How do we – government agencies, academics, conservation organizations, plant industry representatives — use this information to help curtail introductions of plant pests? Can it be integrated into APHIS’ NAPPRA process?
SOURCE
Liebhold, A.M., T. Yamanaka, A. Roques, S. August, S.L. Chown, E.G. Brockerhoff & P. Pyšek. 2018. Plant diversity drives global patterns of insect invasion. www.nature.com/scientificreports/
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
The Old Man – a giant ash tree in Wytham Woods; photo from https://theoldmanofwytham.com/2018/11/29/ash-dieback-in-wytham-woods/
I campaign for protecting trees – especially trees growing to their natural capacity in the habitats in which they have evolved. I focus on the threat to these trees from non-native insects and various pathogens (fungi, nematodes …). I have often expressed my distress because others appear to place a low priority on this goal. I have also asked whether protecting trees might be given a higher priority by more decision-makers if they recognize trees’ vitally important role in countering climate change.
For this reason, I have blogged several times about studies examining the role trees play in sequestering carbon — see here & here & here.
A new study demonstrates that protecting large, old trees – almost by definition in their natural environment – is vitally important. Planting new, small, trees is helpful but cannot substitute for the venerable trees.
Calders and colleagues (full citation at the end of the blog; open access!) have used new technology to update assessments of the amount of carbon sequestered in trees. They conducted their study in a temperate hardwood forest – Wytham Woods, a typical broadleaf temperate forest in Oxfordshire, southern Great Britain. [Wytham Woods is also the site of two of the “Inspector Morse” mysteries – “Secret of Bay 5B” and “A Way Through the Woods”.]
They found that these trees sequester 1.77 times more carbon in their above-ground biomass (AGB) than previously believed based on currently-used models.
One consequence of their findings is that countries using the standard assessment method (which was developed by Robert Bunce in 1968) are reporting inaccurate carbon sequestration estimates to the United Nations per the Paris climate accords. (Calders et al. believe that calculations for conifer species are probably more accurate than those for deciduous forests.)
A second consequence is that death of large trees – from whatever cause – will result in greater loss of carbon storage than previously thought.
Old v. New Measurements
The underlying Bunce dataset and algorithm applied in most European biomass estimates were based on a small sample: 200 trees belonging to five taxa growing in one forest area. The models were derived by cutting down trees and weighing them to determine tree biomass. Smaller trees were used because they are easier to process. The scientists then extrapolated the biomass of bigger trees based on the assumption that correlation between tree size and mass is independent of tree size. This assumption has rarely been tested because of the difficulty and expense of carrying out this type of destructive sampling.
The higher estimates of carbon storage in Calders et al. arise in part from the bias towards small trees in calibration of the earlier models. Calders et al. found that trees do not follow a size-invariant scaling relationship, particularly at larger size; it is important to include crown area. Thus, Calders and colleagues calculated a higher sequestration rate for trees in Wytham Woods that fell within the size range used in developing the Bunce allometric model.
In addition, changes in forest management have increased the abundance of larger trees compared to the 1960s when Bunce carried out his study. Indeed, many of the trees in Wytham Woods are nearly twice as large as the trees used in the original calculation of biomass. The median dbh in Bunce (1968) is 8.4 cm; the mean dbh for the TLS dataset (based on a 2015 inventory) is 15.9 cm. The large trees represent a high proportion of the above-ground biomass: 50% of AGB in Wytham Woods was associated with fewer than 7% of the trees (those with dbh greater than 53.1 cm). All these trees were larger than the trees used to calibrate the widely used allometric model.
Calders et al. say that the distribution of tree size (trunk diameter) in Wytham Woods is representative of broadleaved species throughout Great Britain. Basal area had doubled in 40 years from 1974. Thus, the growth trajectory reflected at Wytham Woods – and presumably across Britain – resulted in a net carbon sink of ~1.77tha-1year-1ha in Calder et al’s 3D analysis. This is almost double the ~1tha-1year-1ha derived using the traditional allometric models. .
Methodology
graphic from Calders et al. large maple (green) and oak (blue) trees illustrated by LiDAR images – profiles and location in the forest (indicated by arrows); copyright Ecological Solutions and Evidence
Calder et al. used terrestrial laser scanning (TLS; terrestrial LiDAR) methods & 3-dimensional analysis to derive tree volume and convert this to above-ground biomass (AGB) and carbon sequestration. They scanned 815 live standing trees in Wytham Woods during winter so leaves did not complicate computations. They found:
total volume of these 815 trees was 742.6±3.9m3ha-1.
TLS-derived AGB = 409.9tha-1. This is significantly greater than the 231.9tha-1 resulting from applying the Bunce allometric models.
In sum, 1.77 times more carbon is stored per ha according to this model than carbon values derived through the allometric AGB models developed by Bunce.
Calder et al. describe the threat to European carbon sequestration projections caused by ash dieback. Ash dieback has been spreading across Europe since the 1990s – although the causal agent was not determined until 2006 (Paap et al.). It is killing European ash across the continent. Some of these trees are large – that is, store impressive amounts of carbon. In Wytham Woods specifically, ash dieback threatens some of the largest trees.
Ash dieback disease was first observed in the United Kingdom in 2012; it reached Wytham Woods in 2017. Ash contributed ~13.2% of the biomass carbon sequestration in the study area. However, the species’ presence in all of Wytham Woods might approach ~34%. Ash comprised 75% of seedlings in 2012. Ash is one of three species that contribute >26% of broadleaved tree AGB & carbon for Great Britain as a whole. The British Woodland Trust expects the UK to lose 80% of its ash trees. As a result, Wytham Woods, Britain, and, by extension, a significant amount of European temperate deciduous forests, are likely to become a substantial carbon source in the next decades.
A dead elm tree on Skelston Moor; photo by Walter Baxter; CC BY-SA 2.0
I note that Europe has already lost any sequestration benefits it would have enjoyed from large elm trees due to “Dutch” elm disease. Various Phytophtoras are killing trees in Britain and Ireland.
I recently described threats to plane trees, pines, and other trees across Europe.
I interpret these findings as demonstrating that protecting large trees growing in natural ecosystems is highly important as we try to cope with climate change. This will require determined, sustained, and strategic actions in the face of disturbances predicted to increase as result of changes in climate and the human activities that contribute to climate change – e.g., overexploitation of natural resources, conversion of natural systems to human use, shipping goods around the globe, …
Calders and colleagues say we cannot afford to lose substantial reservoirs of carbon currently sequestered in temperate forests. Such forests currently account for ~14% of global forest carbon stocks in their biomass and soil. Their importance is growing because of widespread deforestation in the tropics.
What is To Be Done? (to cite Lenin)
Calders and colleagues call for several actions to address potential biases in biomass carbon estimates and drastically improve estimates of forest biomass:
(i) Research to improve knowledge about carbon sequestration levels in trees. This will require
a) greater sampling using such nondestructive methods as TLS to estimate AGB of a wider variety of forest types,
b) improved understanding of wood density, and
c) properly testing the fundamental assumption of size dependency in allometric models.
(ii) Develop empirical models of AGB that do not assume size invariance. This might require. This implies more destructive harvesting to obtain data from a variety of forest compositions, locations, etc,
(iii) Establish a biomass reference network of permanent sample plots specifically designed for estimating AGB. The improved data can then be fed into satellite-derived biomass estimates, which are likely to become the de facto standard for assessing the state and change of forest AGB at large scales. The GEO-TREES database can help. It aims to build on existing long-term ecological plot networks, by including TLS, airborne laser scanning & other ancillary data (including harvest measurements) to specifically allow for upscaling of AGB & development of new empirical models.
(iv) Ensure much better traceability in the use of allometric models. If applying a model to a site at several removes from the original data, e.g., published allometric models, clearly identify where and when the underpinning data were collected, the number and size range of trees from which models were derived, and clarify any assumptions regarding environmental conditions, wood density etc. Database initiatives such as GlobAllomeTree can help.
North American Situation
remains of Michigan’s champion green ash
A study in 2019 (Fei et al. 2019; full citation at end of the blog) has already estimated that 41% of total live (woody) biomass in forests of the “lower 48” states is at risk from the most damaging of introduced pests. The greatest biomass loss was caused by emerald ash borer, Dutch elm disease, beech bark disease, and hemlock woolly adelgid. Before arrival of these non-native pests, mature ash, elms, beech and hemlock were large – providing significant storage of carbon (and other ecosystem services). A complication is that elms and beech, at least, began dying decades before the underlying (Forest Inventory and Analysis; FIA) data began to be collected. Consequently, the reported mortality rates underestimate the actual loss in biomass associated with these pests.
Did Fei et al. rely on biomass estimates based on measurements and algorithms now questioned by Calders et al.? One of the co-authors, Dr. Randall Morin, has told me that USFS scientists are shifting to new models that will result in a slight bump in overall biomass for the U.S. largely because of increased recognition of the biomass in crowns and limbs. However, the new models are based partly on a felled-tree study, so I wonder if they will have similar issues.
Certainly in some situations that threat posed by non-native pests is not yet being adequately incorporated. Badgley et al. (2022) analyzed the California cap-and-trade program to determine whether forest projects enrolled under its provisions can provide sufficiently permanent carbon sequestration. They determined that sequestration losses tied to mortality of one tree species (tanoak; Notholithocarpus densiflorus) due to one disease – sudden oak death – would fully deplete the “buffer pool” set aside to compensate for losses due to disease and insect infestations. This leaves the program unable to provide the promised benefits in carbon sequestration. SOD continues to spread and tanoaks (and other tree species) to die. California along is home to other tree-killing pathogens and insects, e.g., white pine blister rust, Port-Orford cedar root disease, Fusarium dieback, goldspotted oak borer …
California live oak killed by GSOB; photo by F.T. Campbell
Furthermore, the program allows enrollment of forests across the United States, so the multiple pests threatening ash, hemlocks, oaks, and other tree taxa across North America must also be accommodated. I have not even mentioned the likelihood that additional tree-killing pests will be introduced in the future.
How can scientists enhance the credibility of well-intentioned efforts to incorporate forest conservation into strategies aimed at mitigating climate change?
[A separate study by Oxford University has estimated that 2 billion tonnes of CO2 are removed from the atmosphere every year – 99% of it by trees. They point out that this is not sufficient to help Earth avoid temperatures rising above Paris-set levels. See an article by Lottie Limb, Reuters, published 19 January 2023 (sorry – I don’t have a direct link).]
SOURCES
Badgley, G., Chay, F., Chegwidden, O.S., Hamman, J.J., Freeman J. and Cullenward, D. 2022. Calif’s forest carbon offsets buffer pool is severely undercapitalized. Front. For. Glob. Change 5:930426. doi: 10.3389/ffgc.2022.930426
Bunce, R. G. H. (1968). Biomass and production of trees in a mixed deciduous woodland: I. Girth and height as parameters for the estimation of tree dry weight. Journal of Ecology, 56, 759–775.
Calders, K., H. Verbeeck, A. Burt, N. Origo, J. Nightingale, Y. Malhi, P. Wilkes, P. Raumonen, R.G.H. Bunce, M. Disney. Laser scanning reveals potential underestimation of biomass carbon in temperate forest. Ecol Solut Evid. 2022;3:e12197. wileyonlinelibrary.com/journal/eso3 open access!
Paap, T., M.J. Wingfield, T.I. Burgess, J.R.U. Wilson, D.M. Richardson, A. Santini. 2022. Invasion Frameworks: a Forest Pathogen Perspective. FOREST PATHOLOGY Current Forestry Reports https://doi.org/10.1007/s40725-021-00157-4
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Phytophthora ramorum-infected rhododendron plant; photo by Jennifer Parke, Oregon State University
APHIS has released the list of projects funded under §7721 of the Plant Protection Act in Fiscal Year 2023. Projects funded under the Plant Pest and Disease Management and Disaster Prevention Program (PPDMDPP) are intend to strengthen the nation’s infrastructure for pest detection and surveillance, identification, threat mitigation, and safeguard the nursery production system.
APHIS has allocated $62.975 M to fund 322 projects in 48 states, Guam, & Puerto Rico. ~ $13.5 M has been reserved for responding to pest and plant health emergencies throughout the year. USDA is funding ~70% of the more than 460 PPDMDPP proposals submitted.
2 – Target Domestic Inspection Activities at Vulnerable Points $6,356,964
3 – Pest Identification and Detection Technology Enhancement $5,295,125
4 – Safeguard Nursery Production $2,079,119
5 – Outreach and Education $4,131,333
6 – Enhance Mitigation Capabilities $13,875,775
By my calculation (subject to error!), the total for projects on forest pests is ~$6.5 M – or a little over 10% of the total. The top recipient was survey and management of sudden oak death: ~$700,000 for research at NORS-DUC and NCSU plus detection efforts in nurseries of 14 states. Other well-funded efforts were surveys for bark beetles and forest pests (projects in 14 states); surveys for Asian defoliators (projects in 14 states); and outreach programs targetting the spotted lanternfly (10 states, plus surveys in California).
Three states (Iowa, Kentucky and Maryland) received funding for surveys targetting thousand cankers disease of walnut; two states (Kentucky and Maine) obtained funding for outreach about the risk associated with firewood. Funding for the Nature Conservancy’s “Don’t Move Firewood” campaign appears under the home state of its leader, Montana.
Massachusetts obtained funding for outreach re: Asian longhorned beetle. Ohio State received funding for developing a risk map for beech leaf disease.
Ten states received funding for no forest pest projects; I don’t know whether they sought funding for this purpose. These states are Arizona, Colorado, Florida, Hawai`i, Idaho, Minnesota, Nebraska, New Mexico, North Dakota, and Puerto Rico. The “National” funding category also contained no forest pest projects.
Looking at the overall funding level might give a somewhat skewed impression because several of the projects with total funding of ~ $500,000 are actually carried out by USDA agencies. These awards are listed under the state in which the USDA facility happens to be located. Nearly half this money ($213,000) goes to a project by an Agriculture Research Service unit in Delaware to study the efficacy of the biocontrol targetting emerald ash borer. Another $105,588 is allocated to detection of the SOD pathogen (Phytophthora ramorum) in irrigation water, undertaken – I think – at the ARS quarantine facility in Frederick, Maryland. A smaller project at a USFS research facility in Connecticut is studying egg diapause in the spotted lanternfly. The Delaware ARS unit is also pursuing biological control of the red-necked longhorn beetle (RNB) Aromia bungi, which attacks primarily stone fruits. Native to China and other countries in Asia, RNB has been intercepted in wood packaging by the U.S. and Europe; it has become established in Italy and Japan [Kim Alan Hoelmer, ARS, pers. comm.] The APHIS lab in Massachusetts is developing a light trap for detection of the Asian spongy mothsLymantria dispar.
I am intrigued that two states (Mississippi and Nevada) are conducting “palm commodity” surveys. Palms are important components of the environment in some states – although I am not certain these are the two most important!
As you might remember, I am also interested in some invaders other than forest pests. Washington has obtained $998,000 to support two projects integral to its efforts to find and eradicate the Asian (or Northern) Giant hornet. Oregon has obtained funding to carry out a survey for these hornets.
Cactus moth larvae feeding on prickly pear cactus; photo by Doug Beckers, via Flickr
I rejoice to see that the Florida Department of Agriculture continues efforts to deploy biocontrol agents targetting the cactus moth. The Agriculture Research Service is evaluating the establishment of biocontrol agents released to counter two highly invasive plants. Re: Brazilian peppertree, I don’t question the damage it has caused in southern Florida but I have grave concerns should the psyllid and thrips reach Hawai`i. I am most distressed to see that Hawaiian Division of Forestry and Wildlife and Department of Agriculture are actively pursuing deliberate introduction of the thrips. ARS is also searching for potential biocontrol agents targetting the invasive cogongrass (Imperata cylindrica). Penn State is working on registering a soil fungus native to North America, Verticillium nonalfalfae, as a biocontrol targetting the highly invasive tree of heaven (Ailanthus).
Phragmites invading Merkle Wildlife Sanctuary, Upper Marlboro, Maryland; photo by Alicia Pimental, (c) Chesapeake Bay Foundation
APHIS is pursuing biocontrol for “Roseau” cane scale. This situation presents a conflict of geographic regions because the plant to be controlled is Phragmites australis.Phragmitesis highly invasive in the Mid-Atlantic, Northeast, and Great Lakes states . On the Mississippi delta it is considered important in maintaining wetlands crucial to protecting the Louisiana coast from rising seas.
Finally, USDA is pursuing management tools to contain the Box Tree Moth – a threat to the most widely planted ornamental shrub.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Platanus orientalis in Turkey; photo by Zeynek Zebeci
A current issue of the journal Forests (2022 Vol. 13) is a special issue focused on forest pests. This topic was chosen because of increased pest incursions. Choi and Park (full citations at the end of the blog) link this to climate change and increased international trade, as well as difficulties of predicting which pests will cause damage where.
The journal issue contains 15 papers. Several patterns appear throughout. First is the important role of international trade in living plants – “plants for planting” – in introductions. This is hardly news! A second pattern is that at least two North American species were introduced to Europe during the 1940s, probably in wood packaging used to transport military supplies during World War II.
This compilation provides the opportunity to review which organisms of North American origin have become damaging invaders in Eurasia — and sometimes other continents. For example, the journal carries four articles discussing pine wilt disease (PWD). It is caused by the North American nematode Bursaphelenchus xylophilus, and is vectored by wood-boring insects in the genus Monochamus. Beetles introduced from North America and those native to the invaded area are both involved. This disease is considered a severe threat to forest health globally. No apparent association with WWII exists for PWD.
Two fungal pathogens from North America cause serious damage in urban and natural forests of Europe and central Asia. Neither is discussed in the special issue:
Ceratocystis platani has devastated urban trees in the Platanus genus, especially the “London plane” hybrid, and the native European tree, Platanus orientalis. This fungus was accidentally introduced to southern Europe during WWII – as were the two insects described by Musolin et al. It was first reported in northern Italy and Mediterranean France in the early 1970s, but disease symptoms had been observed years earlier. C. platani is established across the northern rim of the Mediterranean and to the east in Armenia and Iran. The worst damage has been in Greece, especially in natural forest stands in riparian areas. Spread of the pathogen there is facilitated by root grafts and by tree wounds caused by floating wooden debris during floods (Tsopelas et al. 2017.)
Platanus orientalis along Voidomatis River in Greece; photo by Onno Zweers, via Wikimedia
Heterobasidion irregulare infects conifers. It has spread and killed large numbers of Italian stone pine (Pinus pinea). The disease was inadvertently introduced to central Italy in the 1940s. H. irregulare has greater sporulation potential and decays wood more quickly than the native congener H. annosum. H. irregulare appears to be replacing the European species; scientists fear it will exacerbate tree infection and mortality rates (Garbelotto, Leone, and Martiniuc. date?)
A third North American pathogen, sooty bark disease (Cryptostroma corticale) has been introduced to Europe. This disease, found on sugar maple in eastern North America, was detected in Great Britain in 1945; it is now throughout Europe (Tanney 2022). EPPO reports that it is widespread in western Europe and in some Balkan countries. The website provides no information on its impact in Europe.
Pests in Russia
A paper authored by Musolin, et al. discusses 14 species of invasive or emerging tree pests found in Russian forest and urban ecosystems. Of these, two are native to North America. Another eight pose a threat to North America if they are introduced here.
As Musolin et al. point out, Russia covers a huge territory across Europe and Asia – stretching 10,500 km, or 6,500 miles. These encompass a great variety of ecological zones. Russia is also actively involved in international trade. It is not surprising, then, numerous non-native organisms have been introduced.
As of 2011, 192 species of phytophagous non-native insects from 48 families and eight orders were documented in the European part of Russia. This number does not include the vast areas in Asian Russia. Additional introductions have probably occurred in the most recent decade. Some of these introduced species have cause significant economic losses. Still, Russia appears to rarely mount a serious control effort.
Of course, the opposite is also true: pests native to some part of Russia can be transported to new regions of Russia or beyond its borders. We North Americans have focused on various species of tussock moths (Lymantria spp., etc.). There are many others. Musolin et al. describe eight in detail. All the information in this blog are from that article unless otherwise indicated.
Two North American Species’ Damage in Eurasia
Both these introductions were detected around the year 2000. Was there some event – other than simply expanding trade – that might explain these introductions?
Leptoglossus occidentalis; photo by nutmeg66 via Flickr
Western Coniferous Seed Bug, Leptoglossus occidentalis
This insect from western North America has invaded Eurasia, North Africa, and Central America. The first detection in Europe was in 1999 in Italy. It spread quickly and is present now from Morocco to Japan, as well as in South Africa and South America. The seed bug is spreading northward in European Russia, including into the forest-steppe zone. Its ability to spread to the East is uncertain.
L. occidentalis attacks a wide range of Pinaceae and Cupressaceae. In the Mediterranean region it has had serious impacts on the pine nut supply (Ana Farinha, IUFRO, Prague, September 2021). In southern parts of Russia it has caused “significant damage”. L. occidentalis also vectors a pathogenic fungus Sphaeropsis sapinea (=Diplodia pinea), which causes diplodia tip blight. The cumulative damage of insect and pathogen to pines can be significant.
The introduction pathway to Russia is unknown. It might have flown from established populations in Europe, or it might have been transported on plants for planting or Christmas decorations.
Oak Lace Bug, Corythucha arcuata
This insect is widespread in the United States and southern Canada. It was first detected in Europe – again, Italy – in 2000. Twenty years later it has spread to almost 20 countries.
Russia was invaded relatively recently; the first outbreak was detected in 2015 in the subtropical zone along the Black Sea coast and Caucasus. Musolin et al. expect the lace bug to spread to natural forests of Central Asia and other countries of the Caucasus. Its spread will be assisted by air currents and movement of plants for planting. The insect is causing considerable aesthetic damage, but other impacts have not been estimated.
Hosts include many species of oak (Quercus spp.), European and American chestnuts (Castanea spp.) plus trees from other botanical families: willows and maples (Salicaceae), redbay (Fagaceae), and alder (Betulaceae).
Pests in Russia that Could Damage North America if Introduced Here
Malus sierversii; photo by Lukacz Szczurowski via Wikimedia
Threat to Apples — Apple Buprestid, Agrilus mali
This Asian beetle has caused extensive mortality of wild apple (Malus sieversii) forests in Xinjiang, China. Wild apple trees are important components of deciduous forests in the Central Asian mountains. The species is also an ancestor of the domestic apple tree. Consequently, the borer is considered a potential threat to cultivated apple trees – presumably everywhere. A. mali might also attack other fruit trees in the Rose family, i.e., Prunus (plums, cherries, peaches, apricots, almonds) and Pyrus (pears).
Unlike most of the other species described here, A. mali is a quarantine pest in Russia and across Europe and the Mediterranean regions – the region where phytosanitary policies are coordinated by the European and Mediterranean Plant Protection Organization (EPPO). Russia bans imports of apple seedlings from infested areas.
China is reported to be experimenting with a possible biocontrol agent, Sclerodermus pupariae (a parasitoid of emerald ash borer).
Threat to Pines and Firs, Already Under Invasive Species Threats
Small Spruce Bark Beetle, Ips amitinus
This European beetle has been considered a secondary pest of dying conifers. Over the last 100 years, it has moved farther North. The first Russian record was 100 years ago, in the region where Russia, Belarus, and Ukraine meet. (Did military action during World War I play a role? This is not discussed by the authors.) By 2022, the beetle occupies 31 million ha. It is probably spread through transport of logs by rail.
In Western Siberia, the spruce beetle has attacked a new host, Siberian pine (Pinus sibirica).
The danger to North America arises from this beetle’s preference for five-needle pines (genus Pinus section Quinquefoliae). North America’s five-needle pines are already under severe pressure from the introduced pathogen white pine blister rust (Cornartium ribicola) and the native mountain pine beetle (Dendroctonus ponderosae).
Four-Eyed Fir Bark Beetle, Polygraphus proximus
This East Asian beetle feeds on firs (Abies spp.). Less commonly, it feeds on other genera in the Pinaceae: spruce (Picea ), pines (Pinus), larch (Larix), hemlock (Tsuga).
This beetle has been spreading west; the first substantiated record in European Russia was 2006 in Moscow. The beetle was probably present in western Siberia in the 1960s, although it was not detected until 2008. Again, the probable pathway of spread is movement of lumber by railroad.
P. proximus vectors an obligate symbiotic fungus, which can rapidly weaken the host. Musolin et al. comment on the beetle’s impacts – which they rarely do in this article. (Does this signify more damaging impacts, or availability of past studies?) They note significant changes in the forests’ ecosystem structure and microclimate, vegetation cover, and local insect fauna.
The danger to North America arises from this beetle’s preference for firs from the sections Balsamea and Grandis. Many North American firs are in these sections, including Fraser fir (Abies fraseri), balsam fir (A. balsamea), subalpine fir (A. lasiocarpa), grand fir (A. grandis), white fir (A. concolor), and others. Several of these firs already are challenged by the introduced balsam woolly adelgid. Firs in central and western Europe are less vulnerable since they are in the section Abies, which the beetle prefers less.
Threats to Poplars
Spotted Poplar Borer,Agrilus fleischeri
This boring beetle is native to northern Asia. It has caused significant mortality in native and exotic Populus plantations in China. Although there have been no reports of this beetle moving beyond its native range, many other Agrilus species have. Canada has twice intercepted adult spotted poplar borers on wood packaging. Musolin et al. fear that the adoption of non-native hosts might trigger an outbreak that would facilitate spread.
Poplar Leafminer, Phyllonorycter populifoliella
balsam poplar; photo by Matt Lavin via Flickr
This micromoth is widely distributed across the Palearctic. It was recently detected on introduced poplars growing in India.
The danger to North America arises from the beetle’s preference for black and balsam poplars. Several species in these taxonomic groups are common in North America, including Populus balsamifera, P. trichocarpa, P. deltoides, and Populus × Canadensis.
Threat to Oaks — Leaf Blotch Miner Moth, Acrocercops brongniardella
This micromoth is widely distributed in Europe and expanding to the north. The pest mines the leaves of several oak species (Quercus spp.), especially English oak, Q. robur; and sometimes European chestnut (Castanea sativa). Leaf blotch miner is considered one of the most important folivore insect pests of oaks in Russia. Damage has been greater in Omsk Oblast (Siberia), where both English oak and the micromoth are introduced species, than in St. Petersburg, which is on the northern limit of their natural range. Musolin et al. fear that the warming climate will lead to the pest causing greater damage in the northern portions of its range.
Threat to Basswood — Lime Leaf Miner, Phyllonorycter issikii
This Asian moth has been moving west since the mid-1980s. It now occupies most of European Russia with some outbreaks in Siberia. In Europe, it is a conspicuous pest of Tilia species.
In these invaded regions, the leaf miner has shifted to novel hosts, including American basswood (T. americana). Basswood is a common plant in the eastern deciduous forest of North America.
Threat to Horse Chestnuts & Urban Trees — Horse-Chestnut Leaf Miner, Cameraria ohridella
This tiny moth was unknown to science before the first recorded outbreak in the late 1980s. Over the next three decades it spread to most of Europe, where horse chestnut (Aesculus hippocastanum)has been widely planted for three centuries. It has caused significant damage.
The first Russian detection was in Kaliningrad, on the shores of the Baltic Sea, in 2003. The leaf miner now occupies 69% of administrative units of European Russia. It is considered one of the Top 100 most dangerous invasive species in Russia.
In North America, the moth might attack native horse chestnuts, Ae. octandra (=flava) and Ae. glabra. Urban plantings are at particular risk because the leaf miner might attack both European horse chestnuts and two non-native maples that have been planted widely, sycamore maple (Acer pseudoplatanus) and Norway maple (A. platanoides). Data cited by Musolin et al. are contradictory regarding larval development on the maples. Once introduced, the leaf miner is difficult to contain because it spreads through natural flight of adults, wind-blown leaves, hitchhiking on vehicles, and movement of infected plants.
Shared Pests
Russia has been invaded by two species that have been introduced in many countries (beyond pine wilt nematode). These two entered the country on plants for planting being imported to landscape venues for the XXII Winter Olympic Games – held in Sochi in 2014.
First to arrive was the Box Tree Moth, Cydalima perspectalis. This East Asian species was first detected outside its native range in Germany in 2006. By 2011 it was widespread in European and Mediterranean countries. In 2021, the boxwood moth was found in North America (first Canada, then the United States). [I discuss the boxwood moth briefly here.]
boxtree moth; photographer unknown
In Russia, box tree moth larvae were first recorded in 2012 on the planting stock of its principal host, Buxus sempervirens. The moth quickly spread around the Black Sea region and to the North Caucasus. It spread farther, too: it reached the Kaliningrad Oblast (southeast coast of the Baltic Sea) in 2020. The main pathway of C. perspectalis invasion was the introduction of infested box-wood planting material.
Further spread of C. perspectalis is likely from Russia into the natural forests across the Caucasus (Transcaucasia) and to countries located further south. This is most distressing because the region has extensive natural forests of Buxus sempervirens. In 2015–2017, C. perspectalis almost completely destroyed the natural boxwood populationsin these regions of Russia and further eastwards in Abkhazia. Boxwood stands in Georgia and northern Iran are already suffering intensive defoliation as the result of infection by two non-native pathogens, Calonectria pseudonaviculata [synonym Cylindrocladium buxicola] and Calonectria henricotiae. Damage to these forests could lead to reductions in soil stability and subsequent declines in water quality and flood protection, changes in forest structure and composition, and declines in Buxus-associated biodiversity (at least 63 species of lichens, fungi, chromista and invertebrates might be obligate). (In December 2022, Iryna Matsiakh presented a compelling overview of threats to these forests in a webinar sponsored by the Horticulture Research Initiative; apparently no recording is available.)
The second global invader to appear was the Brown Marmorated Stink Bug, Halyomorpha halys.
This insect from southeast and east Asia invaded the United States in 1996. The first detection in Europe was in Liechtenstein in 2004. In both cases, it spread quickly across these continents.
Russia’s first detection of stinkbug was in 2014 in parks in Sochi and elsewhere along the Black Sea coast. The spread in Russia appears to have been limited to the Black Sea – Caucasus area.
The brown marmorated stinkbug is highly polyphagous, feeding on more than 300 species of plants. In southern Russia, 107 species have been documented as hosts. At times, stinkbug feeding has caused severe losses in yields of fruit and vegetable crops.
Patterns
Musolin et al. stress the importance of the pest shifting to new hosts–usually from the same or a closely related genus. They cite several examples of these shifts occurring in the pest’s native range, including Agrilus planipennis (from local Asian ash species to introduced North American ash species); Phyllonorycter populifoliella and Agrilus fleischeri (from local poplars to widely cultivated introduced North American poplars and hybrids); Agrilus mali (from cultivated to wild apples).
As I noted above, the introduction and spread pathways are the usual ones: plants for planting (three species) and shipments of logs. There is one indication of wood packaging – Spotted Poplar Borer, Agrilus fleischeri at the Canadian border.
Garbelotto, M., G. Lione, and A.V. Martiniuc. date? The alien invasive forest pathogen Heterobasidion irregulare is replacing the native Heterobasidion annosum. Biological Invasions https://doi.org/10.1007/s10530-022-02775-w
Musolin, D.L.; Kirichenko, N.I.; Karpun, N.N.; Aksenenko, E.V.; Golub, V.B.; Kerchev, I.A.; Mandelshtam, M.Y.; Vasaitis, R.; Volkovitsh, M.G.; Zhuravleva, E.N.; et al. Invasive insect pests of forests and urban trees in Russia: Origin, pathways, damage, and management. Forests 2022, 13, 521.
Tanney, J. Forest Health Challenges Exacerbated by a Changing Climate: Swiss Needle Cast and Sooty Bark Disease in B.C. 65th ANNUAL FOREST PEST MANAGEMENT FORUM (Canada). December 7, 2022.
Tsopelas, P., A. Santini, M.J. Wingfield, and Z.W. de Beer. Canker Stain: A Lethal Disease Destroying Iconic Plane Trees. Plant Disease 2017. 101-645-658 American Phytopathological Society
Spruce budworm (Choristoneura fumiferana); photo by Jerald E. Dewey, USFS; via Bugwood; populations of several forest birds, including Cape May, Tennessee and Bay-Breasted warblers, become more numerous during budworm outbreaks
Now that Drs. Ziska and Aucott have educated us about the strong impact atmospheric CO2 can have on both plants and phytopagous insects, I have asked the experts whether these interactions have been incorporated in the models scientists are using to forecast pest activity in American forests as the climate changes.
The answer is no.
bay-breasted warbler; photograph by Dave Inman at Presque Isle State Park, PA; via Flickr
Dr. Bethany A. Bradley, Co-Director, Northeast Climate Adaptation Science Center at the University of Massachusetts, says empirical models of species range shifts typically only use climate and sometimes other environmental factors (like soils or topography) as predictors of potential geography. Inclusion of demographic processes like how plant growth is affected by more or less water, CO2, competition with other plants etc. would require a lot of data. It is currently impossible since there are tens of thousands of plant species interacting in the forests of eastern North America – and perhaps these factors have been analysed for only a hundred of them.
Mike Aucott points to the same difficulty: inclusion of CO2 in models of the future populations of specific plants would be difficult since the impacts vary from species to species and are compounded by other factors such as soil nitrogen levels, moisture levels, temperature, presence of competing plants, etc.
Regarding insects, Dr. Aucott thinks it is clear that some orders, such as Lepidoptera, don’t fare as well when feeding on plants grown under elevated CO2. He is not aware of efforts to model impacts of high CO2 on specific insects or even orders or feeding guilds.
juniper geometer (inchworm); Dr. Tallamy says inchworms are hairless & good tasting – so sought by birds
Dr. Ziska concurs about the difficulties. Dr. Ziska asks why there is so little funding to study these issues, especially given their probable impact on human food supplies and health – as described in his blog and an opinion piece published in Scientific American two years ago.
I hope that scientists, decision-makers, readers of this blog … maybe even the media! – take into consideration these complexities, even if they cannot be defined.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – [but do not address climate or CO2 aspects] review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Wildfire: one of the widely recognized results of climate change (The Pioneer Fire located in the Boise National Forest near Idaho City, ID began on Jul. 18, 2016 and the cause is under investigation. The Pioneer Fire has consumed 96,469 acres. U.S. Forest Service photo. Original public domain image from Flickr)
A guest blog by Michael Aucott. Mike is a retired research scientist of the NJ Department of Environmental Protection. He has also taught chemistry at the College of New Jersey. He is currently a member of the NJDEP Science Advisory Board Standing Committee on Climate and Atmospheric Sciences, and on the board of directors of the PA/NJ Chapter of the American Chestnut Foundation. If you wish to contact Mike, use the contact button on this website. You MUST include your email address; it is not recorded automatically.
Two major perturbations affect Earth and its living systems, climate change and habitat disruptions. Emerging data show that these are more closely related than previously realized; they are connected by carbon dioxide, CO2.
Climate change basics: the physics
Climate change concerns have focused on the alteration of weather and climate due to the increase in atmospheric concentrations of greenhouse gases, primarily carbon dioxide, CO2. The impact of CO2 on climate has been understood for at least 120 years. In 1896 the Nobel-Prize-winning Swedish chemist Svante Arhennius published calculations demonstrating that human emission of CO2, when combined with the positive feedback effects of water vapor, would warm the Earth (Arhennius, 1896). His equation, ΔF = α ln(C/C0), relates the change in climate “forcing” (the degree to which temperature change is forced) to the ratio of the concentration of CO2 currently in the atmosphere (C) to a previous concentration (C0). This equation is still in use today. Arhennius estimated that a doubling of CO2 would warm the Earth by about 4 degrees C. This estimate is not far off from current estimates based on much more elaborate calculations.
This warming impact is caused by the physics of CO2, water vapor, and other “greenhouse” gases. Infrared radiation causes the CO2, water, and other greenhouse gas molecules to vibrate, leading to the absorption of the energy carried by that radiation. Much of the solar energy coming from the sun is not in the infrared frequency range, so it passes through the atmosphere without being absorbed. However, when this energy is absorbed by the surfaces of the Earth and its biota, and is re-radiated as infrared radiation, it is then absorbed by greenhouse gases, warming the planet.
The amount of water vapor in the atmosphere is directly related to the atmosphere’s temperature: warm air holds more water vapor. Human activity hasn’t directly changed the concentration of water vapor in the atmosphere significantly. But by burning fossil fuels, humans have dramatically increased the atmospheric concentration of CO2 and in so doing, also indirectly increased the concentration of water vapor. Just as Arhennius predicted over 120 years ago, this increase in CO2 is warming the Earth.
Ramifications of this warming include increased heat episodes, the intensification of the hydrological cycle (greater frequency of both heavy precipitation events and of droughts), sea level rise due to the melting of land-based glaciers and the thermal expansion of ocean water, and, almost certainly, intensification of storms and an increase in extreme weather. These climate-warming- based perturbations have the potential to influence the functioning of Earth’s biota in many deleterious ways, and clearly can be associated with the many facets of habitat disruption.
Climate change amplifications: the chemistry
But there’s another aspect of CO2 that may be more important insofar as habitat disruption is concerned and that has been largely ignored: chemistry. CO2 is a trace gas as far as we humans and other animals are concerned, unnoticed by our bodies in normal life. But to plants it is a vital food. It is taken up by plants as an essential input to photosynthesis. In this chemical reaction, using the energy of sunlight, plants combine CO2 and water vapor to make oxygen and carbohydrates, represented with a generic formula of CH2O, according to the equation CO2 + H2O → CH2O + O2. Without this reaction, life as we know it would not exist.
The atmospheric concentration of CO2 has varied over time; some 50 million years ago it was considerably higher than today. However, for at least the last three million years, the concentration of CO2 has been in the range of 280 ppm. Over these millions of years biota have adapted to this concentration. But within the last 300 years, one ten thousandth of this period – a blink of an eye in the geological or evolutionary time scale – the concentration of CO2 has shot up to 420 ppm, a 50% increase, due to humanity’s burning of fossil fuels and forests.
Imagine what might happen to a person who had been on a tight dietary budget for most of his or her life but suddenly got access to 50% more carbohydrates, but no more protein or minerals? We could expect major changes in the metabolism of that person. This dramatic change is what has, in effect, happened to the whole of life on Earth. Our planet’s primary biota, plants, now suddenly have the opportunity to gorge on CO2. But their access to other important substances such as nitrogen has not changed. Evidence is accumulating that CO2 at its elevated level of 420 ppm is not, as has been proclaimed by some, a healthy influence but is instead throwing Earth’s ecosystem into disarray.
Much of the recent experimental evidence on the impacts of enriched atmospheric CO2 has been assembled by Lewis Ziska and presented in his new book, Greenhouse Planet: How Rising CO2 Changes Plants and Life as We Know It (Ziska, 2022; see full citation at the end of the blog). The findings documented in this book reveal a variety of impacts of elevated CO2. These impacts include stimulation of growth of invasive plants, decreases in the nutrient content of major crops, and changes in plants’ production of insecticidal, allergenic, and other compounds. The changing chemistry of plants may be contributing to a major die-off of insects and insect-eating animals including birds. Below are some details.
Habitat Disruptions: Stimulation of Invasive Plants
The generally accepted explanation for why some plants are invasive is that they have been introduced to new regions where their historic predators and parasites aren’t present. Without these drags on their growth, they have flourished. That some alien plants are not browsed by white-tailed deer contributes significantly to their invasiveness in Eastern North America. Other factors are clearly involved as well, including changes in the temperature regime and the availability of water and other resources such as nitrogen.
But elevated CO2 is also a factor. In recent years, techniques for measuring responses of organisms in situ under elevated CO2 conditions have been developed, making possible investigations of the impacts of CO2 concentrations that could exist in the future under otherwise relatively realistic conditions. What the actual atmospheric CO2 concentration will be in 2050 or 2100 is difficult to predict; it depends on what humanity does to control emissions. Various scenarios suggest that levels could exceed 500 ppm by 2050 and might exceed 1000 ppm by 2100 (Tollefson, 2020).
cheatgrass; photo by Jaepil Cho
One study found that the invasive weed Canada thistle, Cirsium arvense, responds more strongly to elevated CO2 than soybean, a crop that it often plagues. In a high CO2 environment, this weed’s root system grows strongly enough to make it significantly more resistant to herbicides (Ziska, et al., 2004) (Ziska, 2010). The highly invasive and dangerously flammable cheatgrass (Bromus tectorum), nicknamed “grassoline” by the U.S. Forest Service because of its propensity to intensify wildfires, also responds strongly to elevated CO2 (Ziska, et al., 2005). Also found to be boosted by enriched CO2 is yellow star-thistle (Centaurea solstitialis), considered one of California’s worst weeds. In one study (Dukes, et al., 2011) this plant grew 600% larger in elevated CO2 relative to ambient, while native plants responded much less strongly or not at all. Japanese honeysuckle, Lonicera japonica, which plagues many areas in the U.S., was found to increase in biomass by 135% at a CO2 concentration of 675 ppm while a similar native plant, coral honeysuckle (Lonicera sempervirens) increased by only 40% (Sasek & Strain, 1991). In a field study also involving Japanese honeysuckle (Belote, et al., 2004), researchers found that its above ground net production (ANPP) approximately tripled under enriched CO2 while other plants in the trial showed showed lesser increases or actual decreases.
Other plants have been found to be selectively encouraged by enriched CO2 including cherry laurel (Prunus laurocerasus), invasive in the Pacific Northwest U.S. and the U.K., (Hattenschwiler & Korner, 2002); dalmation toadflax (Linaria dalmatica), invasive in much of North America (Blumenthal, et al., 2013); honey mesquite (Prosopis glandulosa) , invasive in Australia and parts of Africa (Polley, et al., 1996); and kudzu (Pueraria lobata), which afflicts the Southeast U.S. (Sasek & Strain, 1988). Three plants invasive in China or Southeast Asia, American rope (Mikania micrantha), Creeping oxeye (Wedelia trilobata), and a morning glory species (Ipomoea cairica), were found to produce 70.3% greater biomass when grown at a CO2 concentration of 700 ppm while three corresponding indigenous plants Paederia scandens, Wedelia chinensis and Ipomoea pescaprae, produced only 30.5% more biomass (Song, et al., 2009).
yellow star thistle; photo by Eugene Zelenko
The list goes on of studies showing increased growth of some plants under enriched CO2 conditions. As more in situ investigations are undertaken, it seems likely it will become clearer that today’s enriched level of CO2 is helping some plants to become invasive.
Complexities and contradictory findings exist however. Not all plants are stimulated by enriched CO2. An important difference in the response to higher levels of CO2 is whether a plant has a C3 or a C4 photosynthetic mechanism. C4 plants contain a biochemical pump that concentrates CO2, making them more adapted to low CO2 conditions (Hager, et al., 2016). At current levels of CO2, such plants’ need for CO2 is easily met. C3 plants do not have this CO2 concentrating ability, and so higher levels boost their growth. In a broad meta-analysis of literature, the average response to elevated CO2 of 365 C3 plant species and 37 C4 plant species was noted; the response was significantly increased in C3 species but was unchanged in C4 species (Robinson, et al. 2012). One striking example of such a difference was observed in the field study noted above (Belote, et al., 2004), wherein researchers found that Japanese honeysuckle (a C3 plant) was significantly encouraged by elevated CO2 relative to other plants at the same locale. The same study found that another aggressive invader, Japanese stiltgrass (Microstegium vimineum), a C4 plant, was unaffected or even slightly inhibited relative to competing plants’ growth by elevated CO2.
One finding is widespread; most plants studied under enriched CO2 regimes show an increase in biomass and evince a higher ratio of carbon to nitrogen (C/N ratio) in their tissues and an overall decline in nitrogen concentrations than when grown under ambient conditions. Since nitrogen is a key component of protein, this change can be expected to lead to lowered protein content of critical food crops. Some impacts of this change are already well underway because of today’s elevated CO2 concentration. Changes since 1850 in the C/N ratio and in the estimated protein content of an important plant product, pollen, were discovered in a striking study by Lewis Ziska and colleagues (Ziska, et al., 2016). Using archived museum samples, these researchers determined the nitrogen content of pollen of Solidago canadensis (Canada goldenrod) going back to the 1850s. They estimated that the protein content of goldenrod pollen, a vital nutrient for North American bees, has declined in inverse proportion to the rise in atmospheric CO2, dropping from a concentration of approximately 18% in the mid-1800s to approximately 12% today. They pointed out that it is possible that bees are now unable to provide sufficient protein and other nutrients to larvae, and that one of the main reasons for bee declines is malnutrition caused by enriched atmospheric CO2. Other studies also indicate that elevated CO2 could cause lower nitrogen concentrations in plants and lead to less proteinaceous plant parts, including pollen, being available to plant-feeding insects (Hall, et al., 2005; Knepp, et al., 2007).
bumblebee on goldenrod; photo by Keila
The changing C/N ratio is almost certainly already affecting the human food supply. As documented in an extensive review of published findings (Soares, et al., 2019), elevated CO2 has a considerable impact on the accumulation of minerals and protein in plants, with many plant species showing declines in both quality and quantity of key nutrients. These changes have worrisome implications for human nutrition and may already be responsible for increasing incidences of dietary deficiency in some areas. Lewis Ziska discusses the likely impact of rising CO2 on the future human food supply in his recent post. A number of studies showing declines in protein and also other nutrients such as zinc in food crops important to humanity are also described in Ziska’s new book, Greenhouse Planet, noted above.
Habitat Disruptions: Other Changes in Plant Chemistry
Other changes in plants besides nutritional content may be driven by enriched CO2. Plants produce a variety of secondary metabolites. Most plants use the C3 mechanism; with 50% more available of a key input, some changes in these plants’ production of such chemicals can be expected. Some changes have been observed. Mohan et al. (2006) report that enriched CO2 in an intact forest system increased water use efficiency, growth, and population biomass of poison ivy (Toxicodendron radicans) and that high-CO2 plants also produced a more toxic form of the allergenic compound urushiol.
Quercus chapmanii; photo by Mary Keim at Seminole State Forest, Florida
Many of the phytochemicals plants produce function as defenses against insect predation, and changes in such production have been found to impact herbivore feeding. For example, Landosky and Karowe (2014) suggest that specialist herbivores may have to contend with more effective chemical defenses by plants under elevated CO2. Hall, et al. (2005), in a study involving several oak and one legume species in a scrub oak ecosystem in Florida (see photo above), found that 700 ppm CO2 levels led to decreased damage to plants by four of six insect groups investigated. They did not see increases in plants’ production of carbon-based secondary metabolites, including total phenolic compounds, condensed tannins, hydrolyzable tannins, cellulose, hemicellulose, and lignin however. They concluded that the primary driver of decreased insect predation under elevated CO2 was lower overall plant nitrogen levels. They stated that the decline of nitrogen levels in foliage under elevated CO2 indicated lower foliar quality and hypothesized that the reductions in insect feeding stemmed from the combined effects of nutrient limitation and increases in parasitism and predation on the nutrient-constrained insects. They further stated that although insects try to compensate for lower nutrient content of leaves by eating more, they did not see an increased portion of damaged leaves in their study. These researchers did not report measurements of terpenoid compounds however, which are reported to represent the largest class of secondary metabolites (Wikipedia, 2022). In another study (Hall, et al., 2005a) found that concentrations of condensed tannins were higher in oak leaf litter under elevated CO2, which suggests that enhanced production of insecticidal compounds or other changes to plant tissues could affect not only insects that consume living plant tissue, but also detritivores.
Robinson et al. (2012) also investigated plants’ production of secondary metabolites in their literature review. Looking at all plant groups, they found that under elevated CO2 the production of nitrogen-based secondary metabolites (e.g., alkaloids, cyanogenic glycosides, and glucosinolates) decreased by 16% while the carbon-based secondary metabolites total phenolics, condensed tannins, and flavonoids increased by 19%, 22%, and 27% respectively. Another carbon-based metabolite, terpenoids, declined by 13%. They further divided plants into grasses, shrubs, herbs/forbs, and trees and found differing responses to elevated CO2. Trees, for example, showed increased production of total glycosides and total phenolics, little change in production of total flavonoids, and a decline in the production of total terpenes. Like Hall et al., (2005), Robinson et al. found a strong and significant decrease in nitrogen concentrations under elevated CO2 for C3 plants. A decrease did not show up for C4 plants.
In addition to chemical defenses, plants have physical characteristics such as surface waxes, trichomes, secretory canals, and tissue toughness-enhancing substances such as lignin. All of these features can reduce the edibility of plants for arthropod herbivores. Robinson et al. (2012) found consistent responses to these characteristics under elevated CO2; leaf toughness and specific leaf weight increased by 11% and 18%, respectively, while specific leaf area did not show a significant change. They concluded that there is an increase in general “toughness” of leaves under elevated CO2. As did Hall et al., (2005), Robinson et al. concluded that elevated CO2 will induce changes in plant chemistry, physiology, and morphology that are likely to impact the nutritional quality of host plants for insect herbivores.
Habitat Disruptions: Changes in Plant Chemistry and Insect Decline
Numerous studies have documented a recent and dramatic decline in insect populations and discussed the probable cascading impacts of such declines through the food chain, affecting spiders, lizards, birds, and other organisms (Samways, et al., 2020; Cardoso, et al., 2020; Sánchez-Bayoa & Wyckhuys, 2019; Tallamy & Shriver, 2021). It has been argued that the main drivers of insect species declines are habitat loss and conversion to intensive agriculture and urbanization; pollution, mainly by synthetic pesticides and fertilizers; biological factors, including pathogens and introduced species; and climate change.
But a puzzling aspect is that some insect declines have been observed in nature preserves (Vogel, 2017) that presumably are not greatly affected by most of the above drivers. One example is a study spanning 27 years that found a 76% decline in flying insect biomass at several of Germany’s protected areas subject to rather low levels of human disturbance (Hallmann et al., 2017). Another study in rainforests of Puerto Rico, apparently not subject to influences such as light pollution, habitat loss, pesticides, or agriculture, reported biomass losses between 98% and 78% for ground-foraging and canopy-dwelling arthropods over a 36-year period, (Lister and Garcia, 2018). This leaves climate change as the likely culprit. But although the varied impacts of climate change, including heat episodes, drought, and other episodes of extreme weather could impact insect populations in remote as well as populated areas, the trends observed appear to far exceed the magnitude of such climate-related disturbances over the last several decades.
tent caterpillars; Shiela Brown, Public Domain Pics
Another puzzling aspect is that not all insect orders or feeding guilds seem to be equally affected. Sanchez-Bayoa & Wychuys (2019) whose article reports on a review of 73 historical reports, state that Lepidoptera, Hymenoptera and dung beetles (Coleoptera) appear to be the taxa most affected in terrestrial environments. Robinson et al. (2012) found that phloem feeders such as Homoptera respond positively to elevated CO2 while foliage feeders/Lepidoptera respond negatively. Lepidoptera were among the most impacted; relative growth rate, fecundity, and abundance all declined under high CO2 conditions, while relative consumption rate, total consumption, and development time all increased.
Most Lepidoptera are herbivorous, feeding in their larval stage, caterpillars, on plants. Caterpillars are key components of the terrestrial ecology; in most forests of the world, caterpillars consume more living leaves than all other animals combined (Janzen, 1988). Insect herbivores such as caterpillars are near the hub of most terrestrial food webs, comprising essential food for insect predators and parasitoids, spiders, amphibians, lizards, rodents, bats, birds, and even higher predators such as foxes and bears (Burghardt et al., 2010). At least 310 North American bird species are known to feed extensively on caterpillars, and the majority of terrestrial birds rely on insects during reproduction and other nutrient-limited periods in the annual cycle (Narango, Tallamy & Marra, 2018). Caterpillars and moths are the largest component of nestling diets in hundreds of species of migrant bird species (Tallamy & Shriver, 2021); they are among the “little things that run the world” (Wilson, 1987).
Carolina chickadee; one of the birds Dr. Tallamy focuses on because it feeds its young on caterpillars; photo by Dan Pancamo; through Wikimedia
Habitat Disruptions and Climate Change: Connected by CO2
The apparently heightened rate of decline of insect herbivores such as caterpillars compared to some other insects, and the findings that many declines have been observed in areas relatively unimpacted by direct human influences such as light pollution, pesticides, and land-use change, point to the likelihood of a broad, perhaps ubiquitous, cause. Climate change is such a broad cause. Even broader and more ubiquitous is the main driver of climate change, CO2. Every plant in the world is constantly bathed in an enriched concentration of this gas. A conclusion seems likely: CO2 is not only causing global warming and climate change but is also affecting life on this planet in ways that, while still poorly understood, are already reducing the nutritive value of food crops, may be a significant cause of the spread of invasive plants, and may be the main driver of insect declines and the cascading impacts of such declines on insect-eating animals such as birds.
What to do?
To mitigate climate change and, as argued here, to mitigate habitat disruption, the steady rise in the atmosphere’s burden of CO2 must be halted, and then steps must be taken to lower the current concentration to a healthier level. These are not hopeless tasks. Although what has been a relentless rise in CO2 emissions at the global level continues, increases have slowed and even stopped in some parts of the world. Accelerating the development of low- and zero-carbon energy sources and encouraging energy conservation, as will be done through the U.S.’s Inflation Reduction Act, will further this progress.
More will be needed. Putting a significant and steadily increasing price on the carbon in fossil fuels is arguably the most important next step. Fossil fuels enjoy a free ride. The byproduct of their combustion, CO2, is dumped with little or no restrictions into the world’s atmosphere. A price on carbon would end this inequity. There are ways this could be done in a revenue-neutral (“fee and rebate”) manner that would avoid harm to economies and those with low- and moderate-incomes. A major step forward in pricing carbon by the European Union, a carbon border adjustment mechanism, is close to implementation. For more on this and other developments in cutting CO2 emissions, see the analyses and insights of the Carbon Tax Center and learn more about actions you can take to influence governments with Citizens’ Climate Lobby.
Not discussed here, but another stark example of habitat disruption is the increasing acidification of the world’s oceans caused by the dissolution of atmospheric CO2 in the waters. The ocean’s average pH has dropped from 8.2 to 8.1 within the last 200 years. Because pH is a logarithmic scale, this represents an increase in hydrogen ion concentration of over 25%, a change that is already threatening some marine creatures. More on this is available from many sources; e.g., Kolbert (2014).
References
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Belote, R., J. Weltzin, and R. Norby, 2004, Response of an Understory Plant Community to Elevated [CO2] Depends on Differential Responses of Dominant Invasive Species and Is Mediated by Soil Water Availability, New Phytologist 161, 827-835.
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Burghardt, Karin T., D. W. Tallamy, C. Philips, and K. Shropshire, 2010, Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities, Ecosphere 1: 1-22.
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Hall, M., P. Stiling, D. Moon, B. Drake, and M. Hunter, 2005, Effects of elevated CO2 of foliar quality and herbivore damage in a scrub oak ecosystem. Journal of Chemical Ecology 31, 267-286.
Hallmann, C.A., Sorg, M., Jongejans, E., Siepel, H., Hofland, N., Schwan, H., Stenmans, W., Müller, A., Sumser, H., Hörren, T., Goulson, D., de Kroon, H., 2017, More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS One 12, e0185809.
Hattenschwiler, S. and C. Korner, 2003, Does Elevated CO2 Facilitate Naturalization of the Non-indegenous Prunus laurocerasus in Swiss Temperate Forests?, Functional Ecology 17, 778-785.
Janzen, Daniel H., 1988, Ecological Characterization of a Costa Rican Dry Forest Caterpillar Fauna, Biotropica, 20, 120-135.
Knepp, R., J. Hamilton, A. Zangeri, M. Berenbaum, and E. Delucia, 2007, Foliage of oaks grown under elevated CO2 reduces performance of Antherae Polyphemus (Lepidoptera: Saturnidae), Environmental Entomology 36, 609-617.
Kolbert, E., 2014, The Sixth Extinction, Henry Holt & Co., NY
Landosky, J., and D. Karowe, 2014, Will chemical defenses become more effective against specialist herbivores under elevated CO2? Global Change Biology, 20, 3159–3176.
Lister, B., and A. Garcia, 2018, Climate-driven declines in arthropod abundance restructure a rainforest food web, PNAS 115, E10397–E10406
Mohan, J., L. Ziska, W. Schlesinger, R. Thomas, R. Sicher, K. George, and J. Clark, 2006, Biomass and toxicity responses of poison ivy (Toxicodendron radicans) to elevated atmospheric CO2. PNAS 103, 9086-9089.
Narango, D., D. Tallamy, and P. Marra, 2018, Nonnative plants reduce population growth of an insectivorous bird, PNAS 115: 11549–11554.
Polley, H., H. Johnson, H. Mayeux, C. Tischler, and D. Brown, 1996, Carbon Dioxide Enrichment Improves Growth, Water Relations, and Survival of Droughted Honey Mesquite (Prosopis glandulosa) Seedlings, Tree Physiology, 16, 817-823.
Robinson, E., G. Ryan, and J. Newman, 2012, A meta-analytical review of the effects of elevated CO2 on plant-arthropod interactions highlights the importance of interacting environmental and biological variables, New Phytologist 194, 321-336.
Sánchez-Bayoa, F. and K. Wyckhuys, 2019, Worldwide decline of the entomofauna: A review of its drivers, Biological Conservation 232, 8-27.
Sasek, T. and B. Strain, 1988, Effects of Carbon Dioxide Enrichment on the Growth and Morphology of Kudzu (Puerarialobata), Weed Science 36, 28 – 36, DOI: https://doi.org/10.1017/S0043174500074415
Sasek, T. and B. Strain, 1991, Effects of CO2 Enrichment on the Growth and Morphology of a Native and Introduced Honeysuckle Vine, American Journal of Botany 78, 69-75.
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photo courtesy of Oregon Department of Agriculture
As we know, wood packaging (SWPM; crates, pallets, spools, etc.) is a high-risk pathway for introduction of bark- and wood-infesting insects (borers). (To see my 40 earlier blogs about wood packaging material, scroll down below archives to “Categories,” click on “wood packaging”.) Examples of highly damaging pests introduced to North America include Asian longhorned beetle; emerald ash borer; redbay ambrosia beetle; sirex woodwasp; possibly the polyphagous and Kuroshio shot hole borers; Mediterranean oak borer; and dozens of others. (As of 2014, 58 new species of non-native wood- or bark-boring insects had been detected in the past 30 years [Leung et al. 2014]).
The Asian longhorned beetle and emerald ash borer were probably introduced before the World Trade Organization (WTO) came into effect in 1994; many of the others were detected – if not introduced – after that date. This global trade agreement not only facilitated rapid growth in trade volumes; it also imposed stringent conditions for adoption of plant health (= phytosanitary) measures aimed at preventing pest introductions. (For a review of the WTO restrictions, see my Fading Forests II report, here).
While the risk of pests travelling in raw wood was well known, U.S. and international phytosanitary agencies became aware that wood packaging fit into that category with detection of the ALB in New York and other wood-borer introductions. They acted remarkably rapidly to reduce this risk by negotiating and adopting International Standard for Phytosanitary Measures (ISPM) #15 in 2002.
The goal of ISPM#15 is to “significantly reduce” [not eliminate] the risk of pests associated with solid wood used for constructing packaging (e.g., crates, pallets), from being introduced to other countries through international trade.
This first international standard addressing a pathway of introductions was adopted 20 years ago. (The U.S. fully implemented ISPM#15 in 2006; see either article by Haack for a description of the phase-in period.) So – how great is the risk of pest introduction in wood packaging now? What proportion of these incoming containers are likely to be harboring tree-killing insects? Since it is impossible to reduce that risk to 0 while continuing trade using wood packaging, what is an acceptable level of risk? In determining that level, we must keep in mind the huge volumes of wood packaging being used in international trade, and the serious damage these wood-borers can cause. (See the pest profiles in the links provided above.)
I applaud the international phytosanitary community for acting fast and for choosing a pathway standard rather than try to differentiate the level of risk associated with any particular transaction – given that wood packaging could be made from dozens or hundreds of tree taxa, there are thousands of species of wood-boring insects, and the likelihood of an introduction depends in part on the exporting and importing countries. Plus, international trade involves huge volumes of goods. According to Haack et al. (2022), ~ 55 million TEU (shipping containers measured as twenty-foot equivalents) entered the U.S. in 2020. This is a 68% increase over the volume in 2003. Imports in the first half of 2020 were down because of the COVID epidemic. They then grew rapidly through the first half of 2022; imports from Asia in the first 10 months of 2022 were 21% higher than in the same period in 2019 (Mongelluzzo 2022). Haack et al. (2022) note that the number of countries from which SWPM originated more than doubled from 2003–2004 to 2010–2020, although it dropped after 2018.
In 2014, Haack et al. published an estimate of the pest approach rate in wood packaging as of 2009. Depending on which countries were included and how the time periods were selected to separate pre- and post-adoption of ISPM#15, they reported a 36–52% reduction in the SWPM infestation rate following ISPM#15 implementation. This resulted in an estimated infestation rate of 0.1% (1/10th of 1%). In a recent blog, I applied this estimated approach rate to find that probably 11,000 containers per year transported pests to North America in 2021; 80% of these shipments came to the United States.
Since 2009, traders have gained 13 more years of experience. More important, in 2009 the standard was changed to require that wood packaging be constructed from wood that had been debarked before treatment. There is a tolerance limit for small patches of residual bark. Given that bark provides shelter both for insects already there, and facilitates any new infestation after the treatment was performed, it was expected that this change would further reduce the pest risk.
Since more than a decade has passed since the original analysis, and wood-borers continue to be found in wood packaging – in the U.S. and elsewhere – Haack and colleagues have re-analyzed the pest approach rates (see Haack et al. 2022). Their objectives were to
(2) compare the borer detection rates individually for three kinds of imports and key US trading partners;
(3) see whether wood borer presence varies by season; and
(4) assess the diversity of borer taxa detected overall, and by cargo category and country of origin.
Over the entire 17-year period 2003 – 2020, 87,571 consignments met the conditions for the study: they contained wood packaging that bore the ISPM#15 mark (from 2006 and onwards) indicating it had been treated as required; and the shipment was not from Canada (the U.S. does not require wood packaging from Canada to comply with ISPM#15).
They analyzed the data for the entire 17-year period and separately for four phases:
1) before the U.S. implemented ISPM#15 (2003-2004);
2) phasing-in of U.S. implementation (2005 – 2006);
3) full implementation – but without any restriction on THE presence of bark (2007-2009); and
4) full implementation with restrictions on bark (2010 – 2021).
Over the period 2003– 2020, wood borers were detected in 180 of the 87,571 consignments, or 0.21%. This was 38% less than the 0.34% infestation rate in 2003-2004, before the U.S. implemented ISPM#15. Still, the US had required China to treat its wood packaging as of December 1998 because of introduction of ALB. However, the reduction was greatest in the first phase (2005-2006); in subsequent periods the pest approach rate inched back up. Detection rates have been relatively constant since 2005 despite the requirement in 2009 that bark be removed and a resulting reduction in the presence of bark (it fell from 40% or more of inspected consignments before 2009 to 15% after 2010).
Unfortunately, the data used in the study do not indicate if borers detected on wood were located under any bark that was present. There might be some indication from the species detected: 100% of Scolytinae identified to genus or species detected before 2007 were true bark beetles (which develop primarily under bark), but only 23% in 2010–2020 period.
The data revealed no strong seasonal pattern.
Types of Wood Packaging
The study findings indicate that crates are the type of wood packaging most likely to be infested by insects. While crates constituted only 7.5% of the wood packaging inspected, they made up 29.4% of the infested packaging – or four times greater than their proportion of the dataset. Pallets constituted 88.6% of the inspected wood packaging, but only 67.2% of the infested shipments. Dunnage and “other” wood packaging made up insignificant proportions of both total wood packaging inspected and wood packaging found to be infested. (Of course, dunnage can still pose a threat; see my blog about issues in Houston with dunnage bracing breakbulk cargo.) The Haack et al. (2022) study did not examine dunnage accompanying breakbulk shipments.
Records of Various countries
The 180 infested consignments originated from 30 countries. For two of these countries, the percentage of wood packaging found to be infested was higher than the proportion of all wood packaging from that country that was inspected. Packaging from China made up 4.6% of all shipments inspected, but 22% of the 180 consignments with infested wood packaging. Thus the proportion Chinese consignments with infested wood is five times greater than expected based on their proportion of the dataset. The rate of wood packaging from China that is infested has remained relatively steady – as I noted above. The Chinese infestation rate was 1.26% during 2003–2004, and ranged from 0.58 to 1.11% during the next three periods.
I remind you, again, that the U.S. has required treatment of wood packaging from China since December 1998. Why does this country continue to ship pest-infested wood packaging to the United States? Why are the responsible agencies in the United States not taking action to correct this problem? (DHS Bureau of Customs and Border Protection enhanced its enforcement in 2017; see my blogs.)
A second country with a record of non-compliant wood packaging – Italy – has done better. The level of pest detection still exceeded their expected proportional level – that is, Italy constituted 12.7% of all inspected shipments, but had 15% of infested consignments. Still, Italy has reduced detection rates by almost two-thirds over the 17 years of the study. The Italian statistics would have been even better if there had not been a spike of infested wood in 2015 – 2018 – for unknown reasons.
The data indicate that a third country, Mexico, has improved the pest-free quality of wood packaging accompanying it exports.
Wood from Costa Rica and Turkey has deteriorated as regards pest infestation rates.The borer detection rate on Costa Rican shipments rose from 0.072% during all of 2003–2009 to 0.665% during 2010–2020. Pest-detection rates for Turkey were actually 0 during 2003–2004 (only 59 consignments) but rose to 1.05% during 2010– 2020.
Disturbing Trends
The data reveal other trends that I find disturbing:
While the pest approach rate has fallen since U.S. implementation of ISPM#15, the extent of the decline has progressively decreased during each period studied: the reduction during 2005–2006 was 61%; during 2007–2009, 47%; during 2010-2020 only 36%.
The 2010 – 2020 pest approach rate was calculated at 0.22%. This is more than double the rate based on 2009 data (0.1%, as stated in the 2014 paper). However, we should be cautious in making this comparison because the 2014 and 2022 studies used different methods (see below). The bottom line, however, is that the approach rate remains too high, in my view. Our forests continue to be exposed to the risk of introduction of highly damaging wood-boring pests. Furthermore, since the number of countries sending us infested wood packaging has increased, those potential pests include insects from a greater variety of countries (biomes).
Given the higher number of countries involved and rising proportion of wood that is infested, it is not surprising that the diversity of wood borers found in wood packaging increased. Cerambycidae were consistently the most commonly intercepted borers – making up just under half of the total for the 17 years. Scolytinae were consistently second, at 39%. Still, all major families of borers had been intercepted throughout the period.
Explanation
From the perspective of protecting our forests, what matters is whether the “current” infestation rate is significantly below the rate before ISPM#15 was implemented. As noted, the infestation rate in the 2010-2020 period (0.22%) is, on first glance, more than twice as high as the 2009 approach rate as calculated in the 2014 paper (0.1%). However, the earlier calculation excluded reports of wood packaging from China and Mexico for reasons given in the 2014 paper. Since these countries are among the top three sources of imports to the U.S., and all have had relatively high levels of infested wood packaging, this difference must have had a significant impact on the final finding.
Indeed, the supplementary materials in Haack et al. (2022) show just such a big impact. When records from China and Mexico are excluded from the calculation, the 2010-2020 approach rate appears to have been even higher — 0.272%. This is a reduction from the pre-ISPM#15 approach rate (0.299%) of only 9% — a quarter of the reduction found when data from China and Mexico were included (note the 36% reduction noted above). This difference in approach rate estimates reflects Mexico’s success in cleaning up its wood packaging (as noted above). Since China had “steady” infestation rates throughout, adding or dropping China had less of an impact.
The data do not show a significant drop in pest approach rates during the period 2010-2020 compared to pre-ISPM#15 levels, which is disappointing. Scientists do not know why this happened. It could reflect many of the reasons discussed in the 2022 paper. Perhaps the most important factor is that reporting data on a consignment basis does not allow us to detect whether the numbers of a pest species present have decreased. [See point 5 below.]
The fact is that a pallet or crate bearing the ISPM#15 mark has not proved to be reliable as to whether the wood is pest-free. (This might be because the wood had not been treated, or that it was, but the treatment failed). All the pests detected in study (after 2006) were in wood packaging bearing the ISPM#15 mark. I have noted in past blogs [click on the “wood packaging” category to bring up blogs about wood packaging and enforcement] that Customs and Border Protection also reported that nearly all the wood packaging in which that they detected insect pests bore the mark.
Conclusions: Haack et al. (2022)
Haack et al. (2022) note that U.S. imports have risen 68% by volume from 2003 to 2020 (with additional growth since; see above); however, borer detection rates have remained rather steady. This, plus the apparently lower number of woodborers established in recent years, suggest that ISPM#15 is helping to mitigate risks. However, the reduction in detection rates is less than hoped. They discuss ten possible explanations. Six of these factors were discussed in the original analysis (Haack et al. 2014); four others are new.
(1) Pest Thermotolerance. Can pests tolerate the heat treatment schedule mandated by ISPM#15? Haack et al. (2022) note that this schedule was based on one intended to kill the pinewood nematode and that it was recognized that some pests might be able to tolerate those conditions (Haack et al. 2014). The authors review the literature and conclude that some of the live borers found in heat-treated wood packaging in the study probably did survive the heat treatment. They note that studies are now under way to test temperatures that are lethal to various borers. I have raised the issue that standards must be based on lethal temperatures that can be achieved in practice; otherwise, they won’t protect forests from introduced pests.
(2) Unintentional non-compliance. The authors concluded that accidental treatment failures are likely. They note that the International Plant Protection Convention (IPPC) has issued guidance on handling and testing during heat treatment and fumigation.
(3) Fraud. The authors conclude that fraud is possible, but that the incidence at the global scale is unknown. Each country is responsible for their own compliance. Unfortunately, there is no effective means for independently testing whether treatments have been applied. Still, we note that all live insects evaluated in this paper were in wood package that bore the required stamp and was apparently compliant.
(4) Post-treatment colonization. Haack et al. (2022) note that adoption of the bark requirements in 2009 was intended to reduce re-infestation risk. They note that fewer true bark beetles (that develop under bark) have been detected in recent years compared w/ ambrosia beetles (that develop in wood). As I noted above, the survey data do not reveal whether insects detected by inspectors were under any remaining bark.
(5) AQIM data collection protocols. The authors note that reporting of wood borer detections by consignment conceals the per-piece infestation rate. There might be many fewer individuals of a pest in a container now – and this is important because fewer individuals pose a lower establishment risk (lower propagule pressure).
(6) Pre-ISPM actions. Some countries had begun requiring treatment of wood packaging before 2003, when data collection for the study began. Thus the approach rate might have already been reduced before ISPM#15 was implemented in the U.S., leading to a smaller apparent change.
(7) Level of detection. All the analyses assumed that the detection abilities of port inspectors remained the same over the 17 years of the study. However, inspectors might have improved their efficacy through improvements in training, inspection techniques, or technology. If so, the apparent impact of ISPM#15 would be lessened in recent years. Haack et al. (2022) say estimating the effectiveness of inspections is not possible in the absence of a “leakage survey” conducted on inspected goods to see how often target pests are missed.
(8) Changing trade partners. Countries have varying levels of effort and efficacy in enforcing ISPM#15.
(9) Varying trees and their associated borers. Countries and global regions are home to different tree species and associated insects. Therefore, changes in trading partners – or forest pest conditions within a country – can affect the number and species of potential pests harbored in the wood packaging approaching our borders.
(10) Practical limits on compliance. Reducing infestation levels to near zero through reliance on application of the ISPM#15 standard would require nearly universal compliance by industry, using highly effective treatments. Haack et al. (2022) note that such compliance levels might be difficult to achieve without either very strong incentives or intensive oversight and significant penalties for noncompliant exporters. I note that I have urged the U.S. to enhance both; link to blogs at least CBP has taken action to step up enforcement.
Haack et al. (2022) call for improved education and outreach by the IPPC, plus greater cooperation and information sharing among trading countries. I note that the Cary Institute is pursuing opening data on treatment facilities’ records so importers can hire the best.
Haack et al. (2022) conclude that ISPM#15 has resulted in marked decreases in rates of borer detection in wood packaging. However, problem areas remain re: some types of commercial goods and exporting countries. Given the enormous and growing volume of international trade, the relatively low risk associated with individual crates or pallets still poses a real risk for pest intro.
Still, they consider that the near global acceptance of ISPM#15 indicates a strong commitment by the world community to minimize movement of wood pests in SWPM through international trade.
Haack et al. (2022) call for several improvements. Some concern data to support analysis of the risk level. First, recording the numbers of infested pieces instead of reporting only consignments would help determine the numbers of insects reaching our borders. They also wish to learn whether when bark is present if it exceeds the current tolerance limits; and the type of treatment applied to each infested piece of wood packaging.
They also note opportunities to improve ISPM#15 implementation and enforcement through training on applying treatments, marking and repairing wood packaging, compiling the required records, and inspecting treatment facilities.
Oregon ash swamp; photo by Wyatt Williams, Oregon Department of Forestr
Faith’s Conclusions
In my view, it is less important whether the current approach rate is exactly 0.22% or somewhat less or more. What is important:
the pest approach rate is not acceptable given the huge and rising volume of imports, potential for introductions from new trading partners (with different insect faunas), and the great damage caused by wood-boring insects.
long-standing enforcement problems have not been resolved (i.e., Chinese wood packaging). Perhaps DHS CBP’s enhanced enforcement will bring improvements. CBP staff expressed disappointment in August 2022.
American government agencies must take more effective action to ensure that trade partners comply with ISPM#15. They should also look more aggressively at other actions to curtail introductions via this pathway, e.g.,
U.S. and Canada refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. Institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
APHIS and CBP and their Canadian counterparts provide guidance to importers on which foreign treatment facilities have a record of poor compliance or suspected fraud – so they can avoid purchasing SWPM from them. I am hopeful that the voluntary industry program described here will help importers avoid using wood packaging from unreliable suppliers in the exporting country.
Encourage a rapid switch to materials that won’t transport wood-borers. Plastic is one such material. While no one wants to encourage production of more plastic, the Earth is drowning under discarded plastic. Some firms are recycling plastic waste into pallets.
The two articles by Haack et al. – 2014 and 2022 – fully describe the methodology used, the structure of USDA’s Agriculture Quarantine Inspection Monitoring (AQIM) program, detailed requirements of ISPM#15, the phases of U.S. implementation, etc. Also see the supplemental data sheet in Haack et al. (2022) that compares the methods used in each analysis.
SOURCES
Haack RA, Britton KO, Brockerhoff EG, Cavey JF, Garrett LJ, et al. (2014) Effectiveness of the International Phytosanitary Standard ISPM No. 15 on Reducing Wood Borer Infestation Rates in Wood Packaging Material Entering the United States. PLoS ONE 9(5): e96611. doi:10.1371/journal.pone.0096611
Haack RA, Hardin JA, Caton BP and Petrice TR (2022) Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Frontiers in Forests and Global Change 5:1069117. doi: 10.3389/ffgc.2022.1069117
Leung, B., M.R. Springborn, J.A. Turner, and E.G. Brockerhoff. 2014. Pathway-level risk analysis: the net present value of an invasive species policy in the US. Front Ecol Environ. 2014. doi:10.1890/130311
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
A special issue of the journal Forests (Vol. 13 2022) seeks to improve understanding of the root causes of exacerbated threats from insect pests. The issue contains 15 papers; most focus on geographic areas other than North America. The journal is open access!
Choi and Park (full citations below) link increased pest risk to climate change and increased international trade. They provide brief summaries of all 15 papers. My focus here is on two articles that provide updates on the status of the emerald ash borer (EAB Agrilus planipennis) in Russia and Ukraine. The article by Davydenko et al. also examines interactions between EAB and the invasive pathogen Hymenoscyphus fraxineus, which causes ash dieback disease. In other blogs I will look at insects linked to North America (both species from North America that threaten forests on other continents, and species in Russia that pose a threat to North America) and at the overall Russian experience.
I blogged about EAB invasion of Russia in April 2021 so this is an update.
Musolin et al. (2022) (full citations below) remind us that the EAB invasions of North America and Russia were detected almost simultaneously: in Michigan and Ontario in 2002 and in European Russia (Moscow) in 2003. They conclude that both invasions probably originated from a common source (most probably China). They date the introduction to the late 1980s or early 1990s; pathways might have been wooden crafts, wood packaging, or ash seedlings. Nate Siegert used dendrological studies to estimate a similar introduction date for the North American invasion.
European ash (Fraxinus excelsior) specimen in Belgium; photo by Jean-Pol Granmont
EAB has spread far in the intervening 30 + years. By early 2022, outbreaks were recorded in five Canadian provinces, 35 US states, 18 provinces and several cities in European Russia, and two provinces in Ukraine (Musolin et al. 2022) Davydenko et al. report that EAB had also established in eastern Belarus, but provide no details.
As demonstrated in the earlier blog and confirmed by Musolin et al. (2022) and Davydenko et al., the EAB has spread much faster to the southwest than directly West and to the Northwest. Davydenko et al. attribute the slower spread in the St. Petersburg area to the colder and wetter climate of this region – which is ~1200 km north of Ukraine. While the EAB reproduces in two cohorts in Eastern Ukraine, to the north the beetle requires more than one year to complete its life cycle, at least two years in the St. Petersburg area. In 2021, Musolin et al. 2021 speculated that pressure by the native parasitoid Spathius polonicus Niezabitowski might also be slowing EAB’s spread in the North. In 2022, Musolin does not address this possibility. (I note that APHIS has approved two Spathius species as biocontrol agents in the U.S.).
Musolin et al. (2022) and Davydenko et al. agree that the EAB poses real threat to ash in central and western Europe. In both the south (Davydenko et al.) and in the northwestern area around St. Petersburg ash grows in continuous stretches, linking Russia or Ukraine to Romania, Hungary, Slovakia, and Poland. These ash consist of both natural woodlands, and extensive plantings of both one of the European ash species, F. excelsior and the highly-susceptible North America green ash (F. pennsyvanica). Furthermore, the EAB is an excellent hitchhiker on vehicles & railway cars. Davydenko et al. also consider the beetle to be a strong flyer. Musolin et al. (2022) cite a separate analysis in stating that EAB can probably invade most European countries. Only some regions of Norway, Sweden, Finland, Ireland, and Great Britain are probably protected by their low temperatures.
Both articles were written too early to consider how the current war in the relevant area of Ukraine might affect spread of the EAB, although we know Ukrainians are cutting firewood. The war has certainly interrupted monitoring and other efforts.
The sources agree on EAB’s severe impacts. Musolin et al. (2022) notes that the beetle has killed millions of trees in the forests and urban plantings in North America, European Russia, and Eastern Ukraine. Davydenko et al. note that the Fraxinus genus is one of the most widely distributed tree genera in North America. They then assert that the EAB could virtually eliminate it. I know that North American scientists agree that the beetle threatens many species in the genus; but do they agree that the genus would be “virtually eliminated”? Davydenko et al. think the EAB could pose similar threat to Euro ash F. excelsior.
Musolin et al. 2022 estimate that potential economic losses in Europe could reach US$1.81 billion. By this indicator, the species ranks fourth among the most “costly” invasive pests. Russia spent an estimated US$258.9 million between 2011 and 2016.
areas of Ukraine where studies conducted
Species’ varying vulnerability
Musolin et al. (2022) cite experience in the Moscow Botanical Garden as showing that only two Asian species — Chinese ash, F. chinensis, and Manchurian ash, F. mandshurica — are were resistant to the EAB. The beetle killed both North American ash (i.e., F. pennsylvanica and F. americana) and European ash (i.e., F. excelsior, F. angustifolia, and F. ornus).
Experience in the field in Ukraine (Davydenko et al.) suggests that F. excelsior is less vulnerable to EAB than F. pennsyvanica. The overwhelming majority of EAB infestations were found on the American species. Furthermore, although similar densities of EAB larvae were found in colonized branches of both species, the proportion of larvae that were viable was significantly higher on F. pennsyvnica (91.4%) than on F. excelsior (76.1%). However, the reverse was found in the Moscow and St. Petersburg regions. Davydenko et al. don’t address directly whether they think this discrepancy is attributable to climatic factors or to differences in vulnerability between trees growing in native forests vs. human plantings. They did note that all observed cases of infestation of the native F. excelsior in Ukraine occurred in artificial plantings rather than in natural woodlands.
Davydenko et al. studied parts of Eastern Ukraine where EAB was entering areas already infected by the invasive ascomycete fungus Hymenoscyphus fraxineus (cause of ash dieback, ADB). [Two of these regions — Luhansk and Kharkiv – have been the very center of the current war.] Other studies have shown that ~1 to 5% of F. excelsior trees exhibit some resistance to ADB. These trees are thus a potential foundation for future propagation and restoration of ash in Europe – if enough of them survive attack by EAB.
They found that F. excelsior is more resistant to EAB than F. pennsylvanica, but more susceptible to ADB.
The Luhansk and Kharkiv regions have both EAB and ADB; the Sumy region has only the pathogen. EAB probably invaded the Luhansk region by 2016 (although it was detected only in 2019). The proportion of ash trees (both native and introduced species) infested rose from ~ 10–30% in 2019 to 60 – 90% by 2020–2021. The EAB arrived later in the Kharkiv region, to the Northwest, but the proportion of infested trees was similar by 2021. Combining the two regions, 75% of F. pennsylvanica trees were EAB-infested, whereas only 31% of F. excelsior trees were.
Frequencies of infections by ADB were the reverse. Pooled data from all three study regions showed 21% of F. pennsylvanica trees were infected vs. 42% of F. excelsior. In the plots invaded by both EAB and ADB (in Luhansk and Kherson regions), 4%of F. pennsylvanica were affected by both invasive species vs. 14% of F. excelsior trees. Davydenko et al. conclude that ADB facilitates EAB attack on F. excelsior trees
The impact of EAB is seen in the fact that overall mortality rates were higher in F. pennsylvanica despite the fact that in the Sumy region mortality rates were higher in F. excelsior because of the disease (EAB was absent from this region). On the other hand, EAB infests and kills F. pennsylvanica trees regardless of their prior health condition (i.e., regardless of presence/absence of ADB).
Still, fewer than half the F. excelsior trees in sites affected by both EAB & ADB (in Luhansk and Kherson regions) have died. Davydenko et al. think the survivors constitute a source of material for eventual propagation. These trees need to be carefully mapped – a task certainly not facilitated by the war!
Davydenko et al. conclude that
1. Invasion of EAB in Ukraine occurred 2–3 years before detection in 2019 [I think this is actually quite prompt for detection of EAB invasions]; the invasion is currently expanding both in terms of newly infested trees and invaded geographic area.
2. Fraxinus excelsior (at least when growing in the interior of forest stands) is more resistant to EAB than F. pennsylvanica (when growing in field shelterbelts).
3. Fraxinus excelsior is more susceptible to ADB than F. pennsylvanica.
4. Infection by ADB is likely to predispose F. excelsior to infestation by EAB.
5. Ash trees infected by ADB are predisposed for the colonization by ash bark beetles Hylesinus spp. [I did not discuss these data.]
6. Inventory and mapping of surviving F. excelsior, affected by both ADB and EAB, is necessary to acquire genetic resources for the work on strategic, long-term restoration of devastated areas, thereby tackling a possible invasion of EAB to the EU.
I was surprised that Musolin et al. (2022) think EAB’s host shift from local Asian ash species to introduced North America ash planted in the Russian Far East and China triggered EAB outbreaks in Eastern China that contributed to the beetle’s introduction to North America and European Russia. American scientists apparently agree — Haack et al. (2022) refer to both this episode and a similar to one posited for Asian longhorned beetle (Anoplophora glabripennis) — that widespread planting of Populus plantations led to rapid expansion of ALB in northern China, and the pest-weakened wood was then used in wood packaging.
Davydenko, K.; Skrylnyk, Y.; Borysenko, O.; Menkis, A.; Vysotska, N.; Meshkova, V.; Olson, Å.; Elfstrand, M.; Vasaitis, R. Invasion of emerald ash borer Agrilus planipennis and ash dieback pathogen Hymenoscyphus fraxineus in Ukraine-A concerted action. Forests 2022, 13, 789.
Haack RA, Hardin JA, Caton BP and Petrice TR (2022) Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Front. For. Glob. Change 5:1069117. doi: 10.3389/ffgc.2022.1069117
Musolin, D.L.; Selikhovkin, A.V.; Peregudova, E.Y.; Popovichev, B.G.; Mandelshtam, M.Y.; Baranchikov, Y.N.; Vasaitis, R. North-Westward Expansion of the Invasive Range of EAB, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) towards the EU: From Moscow to Saint Petersburg. Forests 2021, 12, 502. https://doi.org/10.3390/f12040502
Musolin, D.L.; Kirichenko, N.I.; Karpun, N.N.; Aksenenko, E.V.; Golub, V.B.; Kerchev, I.A.; Mandelshtam, M.Y.; Vasaitis, R.; Volkovitsh, M.G.; Zhuravleva, E.N.; et al. Invasive insect pests of forests and urban trees in Russia: Origin, pathways, damage, and management. Forests 2022, 13, 521.
Siegert, N.W. 2006. 17th USDA Interagency Research Forum on Gypsy Moth and Other Invasive Species. Annapolis, MD. January 10-13, 2006.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
The U.S. Geological Survey (USGS) has published an updated register of introduced species in the United States. The master list contains 14,700 records, of which 12,571 are unique scientific names. The database is divided into three sub-lists: Alaska, with 545 records; Hawai`i, with 5,628 records; and conterminous (lower 48) United States, with 8,527 records.
The project tracks all introduced (non-native) species that become established, because they might eventually become invasive. The list includes all taxa that are non-native everywhere in the locality (Alaska, Hawai`i, or 48 conterminous states) and established (reproducing) anywhere in that locality.
Each record has information on taxonomy, a vernacular name, establishment means (e.g., unintentionally, or assisted colonization), degree of establishment (established, invasive, or widespread invasive), hybrid status, pathway of introduction (if known), habitat (if known), whether a biocontrol species, dates of introduction (if known; currently 47% of the records), associated taxa (where applicable), native and introduced distributions (when known), and citations for the authoritative source(s) from which this information is drawn.
The 2022 version is more complete re: plant pathogens than earlier iterations; I thank the hard-working compilers for their efforts!
Hawai`i
wiliwili tree (Erythrina sandwicensis); photo by Forest and Kim Starr
Among the non-native species listed as being in Hawai`i are 3,603 Arthropods, including the following about which I have blogged:
eight species of mosquito in the Hawaiian islands, including the Culex and Aedes species that vector the diseases that have caused extinction of numerous endemic bird species on the Islands.
Also listed are 95 mollusk species and 20 earthworm species. I wonder who is studying the worms’ impacts? I doubt any is native to the Islands.
The Hawaiian list contains 1,557 non-native plant species. Families with largest representation are Poaceae (grass) – 223 species; Fabaceae (beans) – 156 species; and Asteraceae – 116 species. About a third of the plant species – 529 species – are designated as “widespread invaders”. This number is fifteen times higher than the numbers in lists maintained by either the Hawaiian Ecosystems At Risk project (106 species) [HEAR unfortunately had to shut down a decade ago due to lack of funds]; or Hawaiian Invasive Species Council (80 species). Furthermore, some of the species listed by HEAR and HISC are not yet widespread; the lists are intended to facilitate rapid responses to new detections. We always knew Hawai`i was being overrun by invasive species!
Among the 529 most “widespread invaders” are the following from the most introduced families:
Other families have fewer introduced species overall, but notable numbers of the most widespread invaders:
Euphorbiaceae – 8 spp. of Euphorbia
Cyperaceae – 6 spp. of Cyperus
Myrtaceae – Melaleuca quinquenervia, 2 Psidium, Rhodomyrtus tomentosa rose myrtle, 3 Syzygium [rose myrtle has been hard-hit by the introduced myrtle rust fungus]
Zingiberaceae – 3spp. Hedychium (ginger)
Anacardiaceae — Schinus molle (Peruvian peppertree); USGS considers congeneric S. terebinthifolia to be somewhat less widespread.
Plus many plant taxa familiar to those of us on the continent: English ivy, privet, castor bean, butterfly bush, Ipomoea vines … and in more limited regions, Japanese climbing fern Lygodium japonicum.
Rhus sandwicensis; photo by Forest and Kim Starr
I learned something alarming from the species profiles posted on the HISC website: the Hawaiʻi Division of Forestry and Wildlife and Hawaiʻi Department of Agriculture are considering introduction of a species of thrips, Pseudophilothrips ichini, as a biocontrol agent targetting S. terebinthifolia. I learned in early 2019, when preparing comments on Florida’s proposed release of this thrips, that Pseudophilothrips ichini can reproduce in low numbers on several non-target plant species, including two native Hawaiian plants that play important roles in revegetating disturbed areas. These are Hawaiian sumac Rhus sandwicensis and Dodonea viscosa. The latter in particular is being propagated and outplanted in large numbers to restore upland and dryland native ecosystems. While the environmental assessment prepared by the USDA Animal and Plant Service says the thrips causes minimal damage to D. viscosa, I am concerned because of the plant species’ ecological importance. Of course, the two Schinus species are very damaging invasive species in Hawai`i … but I think introducing this thrips is too risky. [To obtain a copy of CISP’s comments, put a request in comments section. Be sure to include your email address in your comment; the section algorithm does not include email addresses (how inconvenient!).]
Continental (lower 48) states
Among the 8,500 species listed in the USGS Register for the 48 continental states are 4,369 animals, among them 3,800 arthropods; 3,999 plants; and just 89 fungi. Among the arthropods, there are 1,045 beetles and 308 lepidopterans. The beetles listed include 12 Agrilus (the genus which includes emerald ash borer and goldspotted oak borer.) It does not include the elm zig-zag sawfly USGS staff have not found any publications documenting its U.S. occurrences. Among the microbes are six Phytophthora (P. cinnamomi, P. lateralis, P. pseudocryptogea, P. quercina, P. ramorum, P. tentaculata). Profiles of several of these species are posted at www.dontmovefirewood.org; click on “invasive species”, then scroll using either Latin or common name.
elm zig-zag sawfly; photo by Gyorgy Czoka via Bugwood
Citation:
Simpson, Annie, Pam Fuller, Kevin Faccenda, Neal Evenhuis, Janis Matsunaga, and Matt Bowser, 2022, United States Register of Introduced and Invasive Species (US-RIIS) (ver. 2.0, November 2022): U.S. Geological Survey data release, https://doi.org/10.5066/P9KFFTOD
United States Register of Introduced and Invasive Species;US-RIIS ver. 2.0, 2022
If you would like to contribute to future versions of the US-RIIS, please email the project leaders at us-riis@usgs.gov.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
