January 2023 – Center for Invasive Species Prevention

Protecting ash & hemlock – latest information

nearly dead ash in Shenandoah National Park; photo by F.T. Campbell

I participated in the annual USDA Interagency Invasive Species Research Forum in Annapolis in January 2023; as usual, I learned interesting developments. I focus here on updates re: efforts to protect ash and hemlock

Hopeful Developments re: countering EAB to protect ash

There are hopeful results in both the biocontrol and resistance breeding programs. The overall goal is to maintain ash as a viable part of the North American landscape.

Biocontrol

Juli Gould (APHIS) reminded us that the agency began a classical biocontrol program targetting emerald ash borer (EAB) in 2003 – only a year after EAB had been detected and much earlier than is the usual practice. [Thank you, former APHIS PPQ Deputy Administrator Ric Dunkle!] By 2007 scientists had identified, tested, and approved three agents; a fourth was approved in 2015.

Nicole Quinn (University of Florida) stressed that the egg prarasitoid, Oobius — if it is effective — could prevent EAB from damaging trees. However, it is so small that it is very difficult to sample. One small study demonstrated that Oobius will parasitize EAB eggs laid in white fringe trees (Chionanthus virginicus) as well as in ash. This is important because it means this secondary host is not likely to be a reservoir of EAB.

The numbers

According to Ben Slager (APHIS), more than 8 million parasitoids have been released at 950 sites since the program began in 2007. These releases have been in 418 counties in 31 states, DC, and four Canadian provinces. Still, these represent just 28% of infested counties. Parasitoids have been recovered in 21 states and two provinces.

Rafael de Andrade (University of Maryland) specified that these releases included more than 5 million Tetrastichus in 787 sites; ~2.5 million Oobius in 828 sites in 30 states; ~500,000 Spathius agrili – lately only north of the 40^th parallel. Releases of Spathius galinae began in 2015; so far ~ 470,000 in 395 sites.

Impact

Several presenters addressed questions of whether the agents are establishing, dispersing, and – most important – improving ash survival. Also, can classical biocontrol be integrated with other management techniques, especially use of the pesticide emamectin benzoate.

Dispersal

Several studies have shown that the four biocontrol agents disperse well (with the caveat that Oobius is very difficult to detect so its status is much less certain).

Implementation considerations

De Andrade found that the longer the delay between the date when EAB was detected and release of Oobius, the less likely Oobius will be recovered. Tetrastichus surprised because the higher the numbers released, the fewer were recovered. He could determine no association between recovery of S. agrili and variations in release regime [numbers released; delay in releasing biocontrol agents; or frequency of releases]. He said it is too early to assess Sp. galinae since releases began only in 2015, but he did see expected relationship to propagule pressure – the more wasps released, the higher the number that were recovered. Sp. galinae did surprise in one way: it seemed to perform better at lower latitudes. De Andrade noted he was working data from less than half of release sites. He asked collaborators to submit data!!!!

Initial signs of ash persistence and recovery

Claire Rutledge (Connecticut Agriculture Experiment Station) determined that

More large trees were surviving in plots where the biocontrol agents were released
EAB density was lower at long-invaded sites
Parasitism rates were similar across release age treatments and release/control plots

Gould focused on protecting saplings so they can grow into mature trees which could be sources of seeds to establish future generations. She noted that there are many “aftermath” forests across the northern United States – those dominated by ash saplings.

In Michigan, at a site of green ash, as of 2015 – 2021, EAB populations are still low, parasitism rate by Tetrastichus and S. galinae high. The percentage of saplings that remained healthy was greater than 80%. There were similar findings in white ash in New York: very low EAB larval density; and more than 70% of ash saplings had no fresh galleries. Gould reported that Tetrastrichus impcts could be detected within three years of release.

So, EAB are being killed by the biocontrol agents combined with woodpecker predation; but in their fourth instar, after considerable damage to the trees.

downy woodpecker in Central Park, NYC. photo by Steven Bellovin, Columbia University

Jian Duan reported on two long-term studies in green & white ash in Michigan and New England. His team used the most labor-intensive but best approach to determine EAB larval mortality and the cause – debarking trees – to determine whether the EAB larva were parasitized, were preyed on by woodpeckers, or were killed by undetermined cause, such as tree resistance, disease, or competition. In Michigan, he linked a crash of EAB population in 2010 was caused by Tetrastichus; EAB tried to recover, but crashed again, due to S. galinae. EAB larval densities had been reduced to 10 / m². Predation by abundant woodpeckers and the native parasitoid Atanycolus was also important.

In New England, EAB has also declined from 20-30 larvae /m² to ~ 10 m².

In Michigan, healthy ash with dbh of larger than 5 inches were much more plentiful in sites where parasitoids had been released. Their survival/healthy rate also was much higher in release sites but the difference declined as years passed. In New England there were growing numbers of healthy trees in 2021-22; (almost none in 2017). Duan conceded that he could not prove a direct link but the data points to recovery.

Tim Morris (SUNY-Syracuse) found that white ash saplings continued to die in large numbers, but the mortality rate was significantly below the rate in 2017. Canopy conditions varied; some trees that were declining in 2013 were recovering in 2017. Forty percent of “healthy” ash in 2013 continued recovering in 2021. Few living trees were declining; trees were either healthy or dead. He thinks probably a combination of genetics and presence of parasitoids explains which trees recover. Morris also reported some signs of regeneration.

beaver feeding on ash saplings, Fairfax County, Va;
photo by F.T. Campbell

At this point, I noted that in parts of northern Virginia, beavers have killed ash saplings. Morris reported finding the same in some sites in New York. Perhaps others have, also; my comment was greeted by laughter.

Theresa Murphy (APHIS) looked at integration of biocontrol and insecticide treatment in urban and natural sites. A study of black and green ash in Syracuse, NY Naperville, IL, and Boulder, CO found continued high parasitism by Tetrasticus and S. galinae and woodpecker attacks in trees treated with emamectin benzoate. Researchers could not detect Oobius. By 2020, most of the untreated trees had died but treated trees remained healthy.

Murphy has begun studying integration of biocontrol and pesticides in green and black ash forests. The goal is to protect large trees to ensure reproduction; the biocontrol agents do not yet protect the large trees. This is especially important for black ash because it declines very quickly after EAB invades. Sites have been established in New York, through collaboration with New York parks, Department of Environmental Conservation, and the Mohawk tribe. She is still looking for sites in Wisconsin – where EAB is spreading more slowly than expected.

1 of the infested ash in Oregon; photo by Wyatt Williams, ODF

Max Ragozzino of the Oregon Department of Agriculture reported on imminent release of biocontrol agents targetting the recently detected outbreak there. I am encouraged by the rapid response by both the state and APHIS.

EAB resistance in ash

Jennifer Koch (USFS) said the goal is not to produce populations where every seedling is fully EAB-resistant, but to develop populations of ash trees with enough resistance to allow continued improvement through natural selection while retaining sufficient genetic diversity to adapt to future stressors (changing climate, pests, diseases). The program has developed methods to quantify resistance in individuals.. Initial field selections of “lingering ash” were shown to be able to kill as many as 45 % of EAB larvae. Already green ash seedling families have been produced by breeding lingering ash parents. This first generation of progeny had higher levels of resistance, on average, than the parent trees. Each generation of breeding can increase the proportion of resistance. Although the bioassays to test for EAB-resistance are destructive (e.g., cutting and peeling to count numbers of surviving larvae), the potted ash seedling stumps can resprout. Once the new sprouts are big enough they are planted in field trials to correlate bioassay results with field performers. Poor performers are culled; those with higher levels of resistance remain and become sources of improved seed.

To ensure preservation of local adaptive traits, this process must be repeated with new genotypes to develop many seed orchards from across the species’ wide range. To support this work, concerned scientists are building multi-partner collaborative breeding networks. These organizations provide ways for citizens and a variety of partners to engage through monitoring and reporting lingering ash, making land available for test planting, and helping with the work of propagation.

See Great Lakes Basin Forest Health Collaborative » Holden Forests & Gardens (holdenfg.org), Monitoring and Managing Ash (MaMA) – A citizen-science-driven program for conservation and mitigation (monitoringash.org), and TreeSnap – Help Our Nation’s Trees! for more information.

Resistance levels in some of the first generation progeny were high enough for use in horticulture, where it is important that trees can remain healthy in challenging environments (street trees, city parks, landscaping, etc.). Koch hopes to develop about a dozen cultivars comprising the best-performing trees, appropriate for planting in parts of Ohio, Michigan, Indiana, and Pennsylvania. Local NGO partners are planting some of these promising genotypes in Detroit to see how they withstand EAB attack.

The threat to black ash is especially severe, and this species presents unique difficulties. While scientists found several seedlings from unselected seedlots had killed high levels of larvae, those deaths did not always result in better tree survival. Koch thinks the tree’s defense response becomes detrimental to tree by blocking transport of water and nutrients. She is working with experts in genomics and others, such as Kew Royal Botanic Gardens, to try to identify candidate trees for breeding programs. The genomics work has been supported by APHIS and the UK forest research agency, DEFRA. Michigan and Pennsylvania have supported the breeding work. USFS Forest Health Protection has supported work with black and Oregon ash (see below) (J. Koch, USFS, pers. comm.).

Koch has also begun working with Oregon ash, in collaboration with the USFS Dorena Genetic Resource Center (located in Cottage Grove, Oregon) and other partners.

dead hemlock in Massachusetts; photo by Ian Kinahan,
University of Rhode Island

Hemlock woolly adelgid

Scientists are still trying to find the right combination of biocontrol, chemical treatments, and silvicultural manipulation.

For several years, hope has focused on two has been on two predatory beetles, Laricobius nigrinus and L. osakiensis. Scott Salom (Virginia Tech) reports that release of these beetles over the past 20 years has had a significant impact on HWA density and tree photosynthetic rate and growth. However, Laricobius aredifficult to rear and they attack only the sistens generation of the adelgid. Ryan Crandall (University of Massachusetts) reports it has been difficult to establish these beetles in the Northeast. He links this difficulty is caused by temporary drops in HWA populations after cold snaps.

Scientists now agree that need to find predators that attack HWA during other parts of its lifecycle. Hope now focuses on silverflies — Leucotaraxis argenticollis and Le. piniperda. While both species are established in eastern North America, the clades in the east feed almost exclusively on pine bark adelgid, and have not begun attacking HWA. Biocontrol practitioners therefore collect flies in the Pacific Northwest for release in the east. Salom is increasing his lab’s capacity to rear silverflies and exploring release strategies.

Preliminary evidence indicates that the western clades of Leucotaraxis are establishing, although data are not yet definitive (Havill, USFS).

Detecting the presence of biocontrol agents presents several challenges. Tonya Bittner (Cornell) described efforts to use eDNA analysis for this. Some puzzles have persisted; e.g., at some sites, she detected eDNA but caught no silverflies. This raised the question of long eDNA associated with the original release might persist. Another problem is that the assay cannot separate the introduced western L. nigrinus from the native congener, L. rubus (which also does not feed on HWA). She continues efforts to improve this technique.

Others explored interactions of the biocontrol agents with insecticides. Salom is studying the impact of soil-applied insecticides on Laricobius populations, which aestivate in the soil. Preliminary results showed significant reduction in the beetle’s population under soil drench application but not under soil injection. He has not yet analyzed all the data.

Michigan is trying to prevent spread of HWA from five counties along the eastern shore of Lake Michigan (where HWA was introduced on nursery stock) to widespread hemlock forests in northern part of the state. Phil Lewis (APHIS) is studying persistence of systemic insecticides in hemlock tissues, particularly twigs and needles. The pesticides involved are imidacloprid, dinotefuran, and Olefin. He has found that pesticide levels are highest 18 – 22 months after treatment, then decline. They are significantly higher after trunk injection compared to bark spray or soil treatments. Imidacloprid had higher residues in twigs; dinotefuran in needles. This difference affects the likelihood of adelgids actually ingesting the toxin.

healthy hemlock in experimental gap; Jefferson National Forest, VA; photo by Bud Mayfield, USFS

Bud Mayfield (USFS) reported on his study of silvicultural strategies to support healthier hemlocks. While hemlocks normally thrive in shade, it has been determined that sunlight assists small trees reducing HWA sufficiently to counter the tree’s leaf-level stress. Small sapling hemlocks grown in sunlight fix more carbon and convert it to growth in shoots and trunk diameter.

Mayfield found promising immediate suppression of HWA in large gaps in Georgia and Tennessee. By the third year the saplings were still growing, although their faster growth had attracted more HWA. These findings were less clear farther north in central Virginia and western Maryland – Mayfield thinks because HWA pressure there is lower. However, managers must maintain the gaps by cutting rapidly-growing competing woody species. He plans to test this strategy farther north in Pennsylvania. He is still trying to determine the optimal size of the gap.

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

www.fadingforests.org

Plant Diversity & Invading Insects: Key Relationship has Policy Applications

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.

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

www.fadingforests.org

Saving Old Trees is Key to CO2 Storage

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.

A Fly in the Ointment

ash dieback in Great Britain; cc-by-sa/2.0 – © Adrian Diack – geograph.org.uk/p/6497286

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.

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.

CC BY-SA 2.0

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

(UK) Woodland Trust https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/tree-pests-and-diseases/key-tree-pests-and-diseases/ash-dieback/

Posted by Faith Campbell

www.fadingforests.org

FY 23 Funding of Tree Pest Projects

*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.

Funding by Goal Area

1A – Enhance Plant Pest/Disease Analysis $2,057,174
1S – Enhance Plant Pest/Disease Survey $14,375,000
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 moths Lymantria 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. Phragmites is 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

www.fadingforests.org

Can we work together to curtail introductions of new diseases?

Phytopthora ramorum-infected potted plants; photo by Washington State University

At this year’s USDA Invasive Species Forum I will be seeking to promote a discussion of what American and other stakeholders can do to suppress spread of forest pathogens. I have raised this issue many times before. To see my blogs about the P4P pathway, scroll down below the archives to the “categories”. See especially here and here.

I note that:

Non-native invasive pathogens and pests are decimating forests worldwide, threatening biodiversity & limiting efforts to rely on forests to alleviate impacts of climate change.
Many of the most damaging non-native organisms are pathogens that are especially difficult to detect at borders or to contain or eradicate once introduced.
A principal pathway by which pathogens are introduced is the international trade in living plants, or “plants for planting” (P4P).
Forest pathologists have long advocated a more pro-active approach – but national and international plant health officials have not taken up the challenge. [think Clive Brasier, Bitty Roy, Thomas Jung, Michael Winfield …]

*Austropuccinia psidii* on *Melalecua* in Australia; John Tann via Flickr

At the global level I suggest that we need:

National agricultural agencies, stakeholders, FAO & International Plant Protection Convention (IPPC) to consider amending IPPC requirement that scientists identify a disease’s causal agents before regulating it. I think experience shows that this policy virtually guarantees that pathogens will continue to enter, establish, & damage natural and agricultural environments.
National governments & FAO / IPPC to fund greatly expanded research to identify microbes resident in regions that are important sources of origin for traded plants, vulnerability of hosts in importing countries, and new technologies for detecting pathogens (e.g., molecular tools, volatile organic compounds [VOCs]).
Researchers & agencies to expand international “sentinel plants” networks; incorporate data from forestry plantations, urban plantings, etc. of non-native trees.
Application of ISPM#36 to promote use of HACCP programs for plants in trade. (See also my discussion in Fading Forests III – link at end of this blog.)

‘ohi‘a trees killed by rapid ‘ohi‘a death; photo by Richard Sniezko, USFS

We Americans need to

Evaluate efficacy of current regulations – incorporating NAPPRA & Q-37 revision. Rely on AQIM data. Include arthropods, fungal pathogens, oomycetes, bacteria, viruses, nematodes. Include threats to U.S. tropical islands (Hawai`i, Puerto Rico, Guam, etc.) which are centers of plant endemism.
Apply existing programs (e.g., NAPPRA, Clean Stock Network, post-entry quarantine) to strictly regulate trade in plant taxa most likely to transport pests that threaten our native plants; e.g., plants belonging to genera shared between North American trees & plants on other continents.
Recognize that plant nurseries are incubators for microbial growth, hybridization, and evolution; require nurseries to adopt sanitary operation procedures regardless of whether they sell in inter-state or intra-state commerce

I will explain my sense of urgency by noting the many recent introductions of pathogens – most probably via P4P or cut vegetation:

13 outbreaks of Phytophthora-caused disease in forests and natural ecosystems of Europe, Australia and the Americas. Three of four known strains of P. ramorum are established in U.S. forests.
Myrtle rust (Austropuccinia psidii) has been introduced to 27 countries, including the U.S., Australia, and South Africa.
Two new species of Ceratocystis (C. lukohia & C. huliohia)—causal agents of rapid ‘ohi‘a death (ROD) – spreading on the Hawaiian Islands. The former species appears to have originated in the Caribbean; the latter in Asia.
Since 2012, beech leaf disease has spread from northeastern Ohio to Maine.
Boxwood blight (caused by 2 ascomycete fungi, Calonectria pseudonaviculata & C. henricotiae) introduced to at least 24 countries in 3 geographic areas: Europe / western Asia; New Zealand, North America.
ash dieback fungus (Hymenoscyphus fraxineus) has spread across Europe after introduction from Asia.

What do you think? Can we find more effective methods to curtail introductions?

Posted by Faith Campbell

www.fadingforests.org

America & Russia – Sharing the Pests

*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.]

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.

SOURCES

Choi, W.I.; Park, Y.-S. Management of Forest Pests and Diseases. Forests 2022, 13, 1765. https://doi.org/10.3390/f13111765

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