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Calamity in Pacific Island Forests

We know the dire threats to Hawaiian forests from pathogens. Some threaten the most widespread tree – ohia. Others are insects threatening trees and shrubs in the remnant dryland forests.

The forests of smaller islands of the Pacific also appear to be facing severe threats – although I have been unable to find information on the current situation.

Guam and its Neighbors

The forests of Guam, Palau, and others in the Western Pacific are among those threatened.

They are geographically isolated and hard to reach, but that distance has not protected them from biological invaders. Their predicament illustrates the dominant role of global movement and trade in spreading pests. In this case, it’s mostly trade in ornamental plants.

These islands have unique flora and fauna. And true to invasive species experts’ expectations, they are vulnerable to bioinvaders. Guam’s most famous invasive species is the brown tree snake (Boiga irregularis), which over a few decades eradicated many bird species and the only native terrestrial mammal, the fruit bat.

Less known, but equally damaging, have been a group of insects that are decimating Guam’s native forest flora.

The most widespread arboreal species in the forests of Guam and neighboring islands is the Micronesian cycad, Cycas micronesica. Its range is Micronesia, the Marianas Group including Guam and Rota Islands; and several of the western Caroline Islands, e.g., Palau and Yap (Marler, Haynes, and Lindstrom 2010).

These forests have already absorbed severe habitat destruction as the sites of fierce fighting in World War II and – in some cases – construction of large military bases. Still, cycads were the most common species in the forest as late as 2002 (Moore, A., T. Marler, R. Miller, and L. Yudin. Date uncertain).

The Worst Pest: Asian Cycad Scale

The most severe current threat to the cycads are introduced insects, especially the Asian cycad scale Aulacaspis ysumatsui.

The cycad scale is native to Southeast Asia. It was first detected on Guam in 2003, when officials noticed that cycads planted near hotels had begun to die. However, this scale had already been spreading thanks to the trade in ornamental cycads. It was detected in Florida in 1996, on Hawai`i in 1998. It continued to spread rapidly in the western Pacific: to Rota in 2007, Palau in 2008 (University of Guam 2012). By late 2019, the scale had spread globally – numerous islands and neighboring mainland areas in the Caribbean (including Puerto Rico and US Virgin Islands), several US states in the Southeast, California, and Taiwan (Moore, Marler, Miller, and Yudin. Date uncertain.) and South Africa. (vanWilgen, et. al. 2020) Also, see the map prepared by CABI.

In every case, the scale has apparently been spread on nursery stock. It is difficult to contain by standard phytosanitary measures – visual inspection – because the scale is tiny and hides deep in the base of the plant’s stiff leaves and other crevices. (Marler and Moore 2010)

By 2005 the scale was killing the native cycad on Guam. Within four years, the millions of C. micronesica on Guam were reduced by more than 90% (Marler, T.E. and K.J. Niklas. 2011). The last time cycads on Guam reproduced in any significant number was in 2004 (Marler and Niklas 2018).

The severe impact of the scale was so rapid that the International Union for Conservation of Nature and Natural Resources (IUCN) changed its listing of C. micronesica from “near threatened” in 2003 to “endangered” in 2006. (IUCN Red List of Threatened Species Online 2008).

Scientists have made several attempts to introduce a biocontrol agent. However, the most promising – the lady beetle Rhyzobius lophanthae – has failed to control the scale, despite having become virtually ubiquitous on Guam. The beetle is too big to reach the significant proportion of scale insects living in small cracks and voids within the plant structures. Evidence from another cycad species indicates that the beetles also don’t prey on scale insects living beneath trichomes (fine hairlike structures on the leaves) or on parts of the plant close to the ground. (Moore, Marler, Miller, and Yudin. Date uncertain.).

Attempts to introduce a second biocontrol organism – the parasitoid wasp Aphytis lignanensis – were stymied by the presence of R. lophanthae (Moore, Marler, Miller, and Yudin. Date uncertain).

Micronesian cycad
photo by Lauren Gutierrez

Other Invasive Species Attacking Cycads

The cycad blue butterfly (Chilades pandava) was detected in 2005 and spread throughout Guam within months (IUCN 2009). Also, it’s been found on Saipan (1996) and Rota (2006). The butterfly is native to southern Asia from Sri Lanka to Thailand and Indonesia. High populations can cause complete defoliation of new foliage. Repeated defoliations can kill the plant. Cycads on Guam are particularly vulnerable because the scale has already caused loss of most of their leaves. Butterfly larvae are often protected by ants (Anonymous).

On cultivated plants the butterfly can be controlled by microbial insecticides containing Bacillus thuringiensis kurstaki (Moore). Scientists at the University of Guam are exploring use of injected insecticides (Moore). They have found an egg parasite, but parasitism levels are low. Any biocontrol agent targetting larvae would have to contend with the ants (Anonymous).

A longhorned beetle (Dihammus (Acalolepta) marianarum) and a snail (Satsuma mercatorius) are also feeding on the cycads (Marler 2010).

The Indo-Malayan termite Schedorhinotermes longirostris was detected in 2011. The termites weaken the cycad stems, which are then toppled by feeding by introduced deer. The termites are also damaging the cycad’s reproductive structures (megastrobili). Termite attacks on cycads surprised scientists since cycads do not form true wood. The termite had probably been introduced recently because, as of 2011, it had been detected only near the Andersen Air Force Base airport (Marler, Yudin, and Moore 2011).

More Isolated – but Still Overrun

Scattered across the Pacific are groups of atolls, including Palmyra and Rose.

Despite their distance from other islands, they have all been visited by mariners for centuries. As a result, they have non-native species, including insects that attack trees.

The tree most affected is pisonia – Pisonia grandis.

The principal insect is another scale, Pulvinaria urbicola. There are some reports that the scale is farmed by ants; species mentioned include several introduced species such as the yellow crazy ant, Paratrechina longicornis.

The scale is probably from the West Indies. Once it reached the Pacific, it might have been distributed to additional islands on seabirds, which travel long distances between the atolls.

The scale’s impact is unclear.

At first, in the mid-2000s, impacts seemed dire. It was reported to be causing widespread tree death on Palmyra and Rose atolls, islands around northeastern Australia, in the Seychelles, and possibly in Tonga.

However, in 2018, scientists reported that eradication of rats on Palmyra Atoll had resulted in an immediate spurt of reproduction of a tree. Numbers of “native, locally rare tree” seedlings (possibly but not explicitly said to be Pisonia grandis) jumped from 140 pre-eradication to 7,756 post-eradication (in 2016). The study made no mention of the scale.

Rose Atoll has only one small island (6.6 ha) with vegetation. Before 1970, it was dominated by Pisonia grandis, but by 2012, there were only seven trees on the island. Several possible causes of this decline have been suggested. Other than the scale, suggested causes include storms, drought, rising sea level / saltwater incursion, and imbalance of bird guano-derived nutrients in the soil. [All information about Rose Atoll is from Peck et al., 2014)

A survey carried out in April 2012 and November 2013 detected 73 species of arthropods from 20 orders on Rose Island, including nine ant species (all but one non-native). Two of these ants – Tetramorium bicarinatum and T. simillimum – were detected tending the scales on Pisonia.

The survey found no evidence of natural enemies of the Pulvinaria scales.

The scientists tested treatment of Pisonia with the systemic insecticide imidacloprid. This treatment apparently reduced scale populations considerably for several months, but then they began to build up again.

In contrast to Palmyra, Polynesian rats (Rattus exulans) were eliminated from Rose Atoll in 1990–1991 – so their role in destroying the trees had ended 20 years before the study. What does the continued decline of the Pisonia trees in subsequent decades suggest for the future of Pisonia trees on Palmyra?

I have sought updates on the tree-pest situations on Guam and the other Pacific islands, but my queries have not received a reply.

SOURCES

Anonymous. 2015. Cycad blue butterfly fact sheet.

Brooke, USFWS, pers. comm. June 3, 2005

CABI November 2019. Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) or the Asian cycad scale. https://www.cabi.org/isc/datasheet/18756 (was formerly Commonwealth Agricultural Bureaux (CAB) International; now apparently just uses acronym)

Marler, T.E. pers. comm. August 15, 2012

Marler, T.E. 2010. Cycad mutualist offers more than pollen transport. American Journal of Botany, 2010; 97 (5): 841. Viewed as materials provided by University of Guam, via EurekAlert; accessed 6 August, 2012.

Marler, T., Haynes, J. & Lindstrom, A. 2010. Cycas micronesica. The IUCN Red List of Threatened Species 2010: e.T61316A12462113. http://dx.doi.org/10.2305/IUCN.UK.2010-3.RLTS.T61316A12462113.en Accessed 22 April, 2020.

Marler, T.E., and A. Moore. 2010. Cryptic Scale Infestations on Cycas revoluta Facilitate Scale Invasions. HortScience. 2010; 45 837-839. Retrieved August 6, 2012 from www.eurekalert.org

Marler, T.E., L.S. Yudin, A. Moore. 1 September 2011. Schedorhinotermes longirostris (Isoptera: Rhinotermitidae) on Guam Adds to Assault on the Endemic Cycas micronesica. https://bioone.org/journals/florida-entomologist/volume-94/issue-3/024.094.0339/Schedorhinotermes-longirostris-Isoptera–Rhinotermitidae-on-Guam-Adds-to-Assault/10.1653/024.094.0339.full

Marler, T.E. and K.J. Niklas. 2011. Reproductive Effort and Success of Cycas micronesica K.D. Hill Are Affected by Habitat. International Journal of Plant Sciences, 2011; 172 (5): 700. Viewed as materials provided by University of Guam, via EurekAlert; accessed 6 August, 2012.

Moore, A. Cycad blue butterfly fact sheet. http://www.guaminsects.net/gisac2015/index.php?title=Cycad_blue_butterfly_fact_sheet accessed 20-4/24

Moore, A., T. Marler, R. Miller, and L. Yudin. Date? Biological Control of Cycad Scale, Aulacaspis yasumatsui, Attacking Guam’s Endemic Cycad, Cycas micronesica. Western Pacific Tropical Research Center University of Guam. Powerpoint http://guaminsects.myspecies.info/sites/guaminsects.myspecies.info/files/CycadScaleBiocontrolAustin.pdf

Peck, R., P. Banko, F. Pendleton, M. Schmaedick, and K. Ernsberger. 2014. Arthropods of Rose Atoll with Special Reference to Ants and Pulvinaria urbicola scales (Hemiptera: Coccidae) on Pisonia grandis trees. Hawaii Cooperative Studies Unit. University of Hawaii. Technical Report HCSU-057 December 2014

University of Guam (2012, August 2). Invasive insects cause staggering impact on native tree. ScienceDaily. Retrieved August 6, 2012, from www.sciencedaily.com-/releases/2012/08/120803094527.htm).

vanWilgen, B.W.,J. Measey, D.M. Richardson, J.R. Wilson, T.A. Zengeya. Editors. 2020. Bioinvasions in South Africa. Invading Nature. Springer Series in Invasion Ecology 14.

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 These reports do not include details on the pest situation on the Pacific islands (including Hawai`i).

Beech Leaf Disease – Inspect Trees for Symptoms! Help Determine the Extent of this Disease

Beech trees have leafed out – so now is the time to search for symptoms of beech leaf disease.

Since its first detection near Cleveland in 2012, BLD has now been detected in 40 counties in Ohio, New York, Pennsylvania, Connecticut, and Ontario. (see map)

I ask your help now because homeowners detected the outbreaks in Connecticut in 2019. (It is often homeowners or curious citizens who detect outbreaks of tree-killing pests.)

What to look for – symptoms:

Dark bands between lateral veins of leaves. Banding is most apparent when viewing from below, looking upwards into the canopy. Banding is evident immediately upon leaf-out in the spring.
Aborted bud development and reduced leaf production.
Later stages result in heavily banded-darkened leaves that are thickened and leathery in texture, often with shriveled or curled edges.

All range of symptoms can be present on the same branch. Symptoms on individual leaves do not advance over the course of the summer. Severely affected leaves can drop off as summer progresses, sometimes as early as June. So the early season – now – is the best time to search.

Cleveland MetroParks has posted a pest alert (from last year), a report on symptom progression with good photos, and instructions for participating in the Beech Tree Health Survey. Survey apps are available as iOS: https://apps.apple.com/us/app/tree-health-survey/id1498515762 or Android: https://play.google.com/store/apps/details?id=com.KentState.TreeHealth&hl=en_US

Go to https://www.clevelandmetroparks.com/parks/education/publications and scroll down to the Beech Leaf Disease section (it is in large font so you won’t miss it).

Where to look? See the map of the range of American beech.

Range of American beech; source Wikimedia

In addition to checking American beech (Fagus grandifolia), also examine European beech (F. sylvatica), and Oriental beech (F. orientalis).

I encourage you to use one of the apps. However, if you are not but see something suspicious, send me a picture by using the “contact us” button. I will take a quick look, consult with experts, and – if they see what appear to be symptoms – they will tell me and I will tell you how to contact plant health authorities in your state or province.

Remember to include your email and phone number in your message to me – the “contact” form by itself does not provide sufficient information for me to respond to you.

Posted by Faith Campbell

Pest Threats to Eastern Forests – Focus on the Mid-Atlantic

EAB-kiled ash tree in Shenandoah National Park in 2016
photo by F.T. Campbell

As we have known for years, forests of the eastern United States are under severe pressure from non-native forest insects and diseases. Several recent studies have put this fact into perspective.

Fei et al. (2019) found that the 15 most damaging introduced species threaten 41.1% of the total live forest biomass in the 48 conterminous states. Nine of the 15 species included in this calculation are pests of the eastern forest. Indeed, the greatest increase in biomass loss, as measured by USDA Forest Service Forest Inventory and Analysis (FIA) plot data occurred here. Compensatory growth in unaffected trees and the recruitment of new regeneration occurs only later – as much as two or more decades after the pest invasions began. Fei et al. (2019) expect these losses will be exacerbated in the future due in part to the likelihood that additional pests will be introduced.

Randall Morin found that non-native pests had caused approximately 5% increase in total mortality, by tree volume, nation-wide.

Most widespread pest threats in the East

Scientists have used several methods of measuring introduced pests’ impacts. One measure is the number of counties where the pest is present. A second measure is the proportion of the volume of the host that has been affected. Both metrics are used by Morin. A third method, used by the CAPTURE Project (Potter et al. 2019a), is the number of hosts affected by the pest.

Morin and colleagues found that the European gypsy moth has invaded 630 counties – or 29% of the volume of its principal host, oaks. (In both cases, the gypsy moth trailed white pine blister rust in extent of infestation. The latter is nationwide but having its greatest impacts in the West). The CAPTURE Project found that the gypsy moth affected the largest number of hosts – 65.

Using the “counties invaded” metric, Morin and colleagues found that dogwood anthracnose had invaded 609 counties in the East (and additional areas in the West); the emerald ash borer had invaded 479 counties at the time of analysis; the hemlock woolly adelged had invaded 432 counties. Using the number of hosts impacted measure, oak wilt (Bretziella fagacearum) affected the second largest number of hosts – 61 (Potter et al. 2019a). [All these pests are described briefly here.]

Project CAPTURE (Potter and colleagues 2019a) evaluated 339 serious pests threatening one or more of 419 native tree species in the continental US. They included both native and introduced pests. They analyzed 1,378 pest-host combinations. They found that:

54% of the host tree species (228) are infested by an exotic pest – although only 28% of the 1,378 host/agent combinations involved pests are known to be non-native in origin.
Exotic agents have, on average, considerably more severe impacts than native pests.
Non-native pests had greater average severity on angiosperms than on conifers. (As an earlier blog documented, Mech and colleagues have reached a similar – although tentative – conclusion.)
Their estimate of the threat posed by non-native pests to forests – especially for the East – is an underestimate because established pests could spread to additional vulnerable areas and there is a high likelihood that new pests will be introduced. The Southeast was consistently a “coldspot” – despite the near extirpation of one understory tree – redbay.

Potter et al. (2019a) ranked forest threats in two ways. Four host families were at highest risk to alien pests, as measured by both the numbers of tree species affected and by the most host/agent combinations: Fagaceae (oaks, tanoaks, chestnuts, beech); Pinaceae (pines); Sapindaceae (soapberry family; includes maples and buckeye); Salicaceae (willows, poplars, aspens). When host families were ranked by the severity of the host/pest threat, Fagaceae was still at greatest risk, and Sapindaceae was still in the top four; however, Ulmaceae (elms) and Oleaceae (includes Fraxinus) replaced pines and willows.

A very interesting study was published by scientists based in the Blue Ridge Mountains of Virginia (Anderson-Teixeira et al. 2020). They contend that their area is a good example of what is happening more broadly in the Mid-Atlantic region.

Anderson-Teixeira et al. (2020) found that non-native pests have substantially impacted at least 24% of the 33 tree genera (eight genera) recorded as present in their study plots. They estimated that over the century beginning with the appearance of chestnut blight in the region and ending with the expected extirpation of ash trees, net live aboveground biomass (AGB) loss among affected species totaled roughly 6.6–10 kg m -2. Forty to sixty percent of this loss started before the Park initiated quantitative surveys of permanent plots in 1987. The authors estimated that chestnut contributed up to 50% of estimated AGB losses over the century. Consequently, the estimate has very high uncertainty.

Despite these losses, Anderson-Teixeira et al. (2020) found that both total aboveground biomass and diversity within individual study plots had largely recovered through increases in non-vulnerable genera.

Average above ground biomass across the plots established in Shenandoah National Park increased as the forest recovers from logging, farming, and other disturbances before formation of the Park. These increases were due primarily to reproduction and growth of tulip poplar (Liriodendron tulipifera) and growth (but not reproduction) of oaks. Net AGB biomass was lost in oak- and hemlock-dominated plots. At plots established in the neighboring Smithsonian Conservation Biology Institute, pests had caused relatively minor impacts on AGB.

Diversity of tree species also did not change much. In the Park, the average number of genera per plot declined only 3% between 1991 and 2013. Diversity at the landscape scale increased by two genera – from 26 to 28. Many individual plots, though, lost three genera due to non-native pests – chestnut, redbud, and hemlock. A fourth genus was lost due to stochastic change. At the same time, the plots gained six native genera). This finding might be skewed by the short duration of the study period, which missed initial declines in several taxa and captured only the initial stages of decline in ash.

Several taxa were lost from the monitoring plots but were not completely extirpated from the region. Even those species not “lost” suffered elevated mortality rates and steep declines in abundance and above-ground biomass. These declines have not been reversed. The exception was some oaks, which regained above ground biomass, but not abundance, following the gypsy moth outbreak in the 1980s and early 1990s.

Taxa-specific findings

(Most of these pests are described briefly here.)

Fei et al. (2019) found that losses in biomass due to non-native pests – as measured by FIA plot data – was greatest for ashes, elms, beech trees, and hemlocks..

Morin and colleagues found annual mortality rates had increased three-fold above background levels for ash, beech, and hemlock. They also calculated the present mortality rates for several species for which the majority of loss occurred before their study (consequently, they could not calculate a pre-invasion “background” rate to which present rates could be compared). These included American chestnut (mortality rate of 7%), butternut (mortality rate of 5.6%), and elm trees (mortality rate of 3.5%).

The CAPTURE Project (Potter et al. 2019a) identified fifteen host-agent combinations with the highest severity. Ten of these species are found in the Mid-Atlantic region:

American chestnut (Castanea dentata)
Allegheny chinquapin (C. pumila)
Carolina ash (Fraxinus caroliniana) ,
pumpkin ash (F. profunda)
Carolina hemlock (Tsuga caroliniana)
butternut (Juglans cinerea)
eastern hemlock (Tsuga canadensis)
white ash (Fraxinus americana)
black ash (F. nigra)
green ash (F. pennsylvanica)

Four of these species are in genera included among the eight genera evaluated in the study conducted in the Blue Ridge (Anderson-Teixeira et al. 2020): American chestnut, butternut, eastern hemlock, green and white ash. The four other genera in the Blue Ridge study were elm (Ulmus), oak (Quercus), redbud Cercis, and dogwood (Cornus). All except redbud are recognized by other sources as heavily affected by non-native pests – confirming Anderson-Teixeira et al. (2020)’s conclusion that findings on the Blue Ridge reflect the wider situation.

Anderson-Teixeira et al. (2020) note that several of these tree species have been declared imperiled by the International Conservation Union (IUCN): American chestnut, butternut, American elm, eastern hemlock, and ash species.

Anderson-Teixeira et al. (2020) report data on three taxa previously important in the canopy of Blue Ridge forests – chestnut, elms, and butternut. Chestnuts larger than 10 cm DBH had disappeared from the future site of Shenandoah National Park by 1910. Short-lived sprouts continue to be present in plots in the low-elevation Smithsonian Conservation Biology Institute. Two elm species were described as ‘‘sparse’’ in the 1939 qualitative survey. Elms have persisted at low densities, low biomass, and increasingly small sizes. Butternut was ‘‘common’’ in 1939, but had disappeared from Shenandoah NP by 1987. On the Smithsonian’s property, butternut declined from four living individuals in 2008 to two in 2018. The near disappearance of butternut reflects the national picture: FIA data show the species has decreased about 58% across its U.S. range since the 1980s – which is decades after butternut canker started having a detectable impact in the Midwest.

In the Park, oak-dominated plots lost on average 24.9% of individuals and 15% of aboveground biomass. After 1995, when the gypsy moth was better controlled by spraying of Bacillus thuringiensis var. curstaki, oak aboveground biomass increased gradually, driven by individual tree growth rather than new recruitment. Continued declines in oak abundance are attributable to oak decline and management actions (or inactions) that do not promote regeneration.

In a separate study, a group of oak experts went through a process of queries to identify the greatest threat to oaks now and in the future (Conrad et al. 2020). They initially identified the following threats as most important currently (descending order): gypsy moth, oak wilt, oak decline, climate change, and drought. The top five future threats were initially identified as climate change, oak wilt, sudden oak death, oak decline, and some unknown new or emerging (non-native) pest or pathogen. By the third round, after the experts thought about their colleagues’ responses, oak decline had replaced gypsy moth as the most critical threat currently. Attack by an unknown new or emerging (non-native) pest or pathogen replaced climate change as the most critical future threat. While there was not a complete consensus, the consensus was stronger on the threat from a new pest.

remnant eastern hemlock at Linderlost, Shenandoah National Park
photo by F.T. Campbell

Anderson-Teixeira et al. (2020) reported that eastern hemlock was initially present in ten of Shenandoah plots, but was no longer recorded in the survey plots after 2007. (More than 20,000 insecticide-treated trees remain alive throughout Shenandoah NP).

Before arrival of the emerald ash borer, ash aboveground biomass was increasing in Shenandoah NP and stable on the Smithsonian Institute. EAB-caused mortality was first detected at the Smithsonian site in 2016 and accelerated steeply thereafter, exceeding 12.5% year by 2018. As of 2019, ash had lost 28% of individuals and 30% of aboveground biomass relative to 2016. Ninety-five percent of remaining live trees were considered “unhealthy’’ (Anderson-Teixeira et al. 2020).

eastern (flowering) dogwood; photo by F.T. Campbell

Unlike many studies, the Shenandoah study included understory species. Flowering dogwood declined by up to 90% from plots on the Smithsonian property; 2008–2019 mortality rates averaged 7.1%. Redbud declined by up to 76% from 1995 to 2018. The 2008–2019 mortality rates averaged 6.2% year.

Anderson-Teixeira et al. (2020) concede difficulty in estimating mortality due to less virulent or lethal pathogens, including Neofusicoccum spp. on redbud and Dutch elm disease on slippery elm.

Nevertheless, they believe their analysis probably underestimates the overall pest impacts because they did not analyze several other pest/host combinations known to be present in the Park: balsam woolly adelgid (Adelges piceae) on high-elevation populations of Abies balsamea; white pine blister rust (Cronartium ribicola) on eastern white pine (Pinus strobus); beech bark disease (Neonectria spp.) on American beech (Fagus grandifolia); thousand canker disease on walnut and butternut; and emerald ash borer on the novel host fringetree Chionanthus virginicus.

Another possible threat to oaks, winter moth (Operophtera brumata), is apparently now being controlled by the biocontrol agent Cyzenis albicans.

I am uncertain about the current status of two Diplodia fungi – Diplodia corticola and D. quercivora – link to blog which have been detected in both Florida and California. In Florida, almost all the symptomatic trees grow in cultivated settings where they are exposed to various stresses (Mullerin and Smith 2015).

However, host range studies indicate that 33 species of oaks and one species of chestnut that grow in the Southeast are vulnerable, to varying degrees, to D. corticola. Oaks in the red oak group (Section Lobatae) are more vulnerable than are white oaks (Section Quercus) (Mullerin and Smith 2015). In the test, the most vulnerable appear to be the following species native to the Southeast: Q. laurifolia, Q. virginiana, Q. geminata, Q. chapmanni, Q. laevis (turkey oak), Q. phellos, Q. pumila, and Q. incana (Dreaden et al. 2016).

What should we do?

Fei et al. (2019) noted that the losses to biomass would be exacerbated by the likely introduction of additional pests. They did not recommend any prevention actions.

Conrad et al. (2020) said their findings “lend support to national regulatory and awareness efforts to prevent the introduction and establishment of novel exotic insects and pathogens.”

Anderson-Teixeira et al. (2020) join others in declaring that future survival of the IUCN-listed species probably depends on conservation and restoration actions. They cite several sources, but not the CAPTURE Project – although the two studies reinforce each other. They specifically mention limiting invasive species’ spread through strengthened regulations and “enhanced plant biosecurity cyberinfrastructure”.

This last recommendation reinforces the message of Bonello et al. (2019) link to publication. We called for creation of a federal Center for Forest Pest Control and Prevention to implement end-to-end responses to forest pest invasions. One focus would be correcting the currently-inadequate focus on detection, development and deployment of genetic resistance while using modern techniques that allow for much faster breeding cycles.

Posted by Faith Campbell

SOURCES

Anderson-Teixeira, K.J., V. Herrmann, W.B. Cass, A.B. Williams, S.J. Paull, E.B. Gonzalez-Akre, R. Helcoski, A.J. Tepley, N.A. Bourg, C.T. Cosma, A.E. Ferson, C. Kittle, V. Meakem, I.R. McGregor, M. N. Prestipino, M.K. Scott, A.R. Terrell, A. Alonso, F. Dallmeier, and W.J. McShea. Date? Long-Term Impacts of Invasive Insects and Pathogens on Composition, Biomass, and Diversity of Forests in Virginia’s Blue Ridge Mountains. Ecosystems

Bonello, P. , F.T. Campbell, D. Cipollini, A.O. Conrad, C. Farinas, K.J.K. Gandhi, F.P. Hain, D. Parry, D.N. Showalter, C. Villari, and K.F. Wallin. 2019. Invasive tree pests devastate ecosystems – A proposed new response framework. Frontiers

Conrad, A.O., E.V. Crocker, X. Li, W.R. Thomas, T.O. Ochuodho, T.P. Holmes, and C. D. Nelson. 2020. Threats to Oaks in the Eastern US: Perceptions and Expectations of Experts. Journal of Forestry, 2020, 14–27

Dreaden, Black, Mullerin, and Smith. Poster presented at the 2016 USDA Invasive Species Research Forum

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. Liebhold. 2019. Biomass losses resulting from insect and disease invasions in United States forests. Proceedings of the National academy of Sciences.

Guo, Q., S. Feib, K.M. Potter, A.M. Liebhold, and J. Wenf. 2019. Tree diversity regulates forest pest invasion. PNAS. www.pnas.org/cgi/doi/10.1073/pnas.1821039116

Morin, R.S., K.W. Gottschalk, M.E. Ostry, A.M. Liebhold. 2018. Regional patterns of declining butternut (Juglans cinerea L.) suggest site characteristics for restoration. Ecology and Evolution.2018;8:546-559

Morin, R. A. Liebhold, S. Pugh, and S. Fie. 2019. Current Status of Hosts and Future Risk of EAB Across the Range of Ash: Online Tools for Broad-Scale Impact Assessment. Presentation at the 81^st Northeastern Forest Pest Council, West Chester, PA, March 14, 2019

Mullerin, S. & J.A. Smith. 2015. Bot Canker of Oak in FL Caused by Diplodia corticola & D. quercivora. Emergent Pathogens on Oak and Grapevine in North America. FOR318

Potter, K.M., M.E. Escanferla, R.M. Jetton, and G. Man. 2019a. Important Insect and Disease Threats to United States Tree Species and Geographic Patterns of Their Potential Impacts. Forests. 2019 10 304.

Potter, K.M., M.E. Escanferla, R.M. Jetton, G. Man, and B.S. Crane. 2019b. Prioritizing the conservation needs of United States tree species: Evaluating vulnerability to forest insect and disease threats. Global Ecology and Conservation. (2019)

Serious Invasive Species Damage to High-Elevation Sites in the West

Dream Lake, Rocky Mountain National Park, with limber pine
photo by F.T. Campbell

In this blog, I summarize two pest threats to the unique ecosystems on high-elevation mountain ridges in the West. At risk are several keystone tree species: the five-needle pines growing at high elevations (“high-five” pines) and subalpine fir. The invasive species causing this damage – white pine blister rust (WPBR; Cronartium ribicola) and balsam woolly adelgid (BWA; Adelges piceae) – are two of the most widespread non-native species threatening North American trees and affecting the highest proportion of host volumes (Morin).

The pines being killed by white pine blister rust are whitebark pine (Pinus albicaulis), limber pine (P. flexilis), Rocky Mountain bristlecone pine (P. aristata), foxtail pine (P. balfouriana), and southwestern white pine (P. flexilis var. reflexa). As of 2010, infestations had not been reported on Great Basin bristlecone pine (P. longaeva) and the Mexican white pine species. [Unless otherwise indicated, information on white pine blister rust is from a comprehensive review and synthesis published in the August 2010 issue of Forest Pathology (Vol. 40:3-4).]

As noted above, sub-alpine fir (Abies lasiocarpa) is also being affected – although less uniformly than the pines – by the balsam woolly adelgid.

Both of these pests arrived approximately a century ago, but they are still spreading and causing additional damage. White pine blister rust had spread widely throughout the West within 40 years of its introduction. Meanwhile, BWA spread among lowland and subalpine firs along the Pacific coast from California to British Columbia within 30 years of its first detection. Its spread eastward was slower, but relentless. It reached Idaho, Montana, Utah and interior British Columbia within 50 years. Also, BWA reached Alaska within 90 years of its introduction in California. These pests are perfect examples of how invasive species introduced long ago are dreaded “gifts that keep on giving”.

For a detailed discussion of these pests’ impacts, see the descriptions posted here. To summarize, though, WPBR is present in the ranges of eight of the nine vulnerable western white pines and has caused severe mortality to some species (Sniezko et. al. 2011). For example, 88% of the limber pine range in Alberta is affected (Dawe et al. 2020). WPBR is generally causing more damage to its hosts’ northern populations. Impact of the BWA are more subtle than WPBR. Also, impacts’ severity is linked to climatic conditions. For example, measurable decline on the Olympic Peninsula was greater on south-facing slopes. However, the study did not determine whether this reflected heat-loading and tree stress or more abundant subalpine fir on these slopes. An estimated 19-53% (average 37%) of subalpine fir trees had died on sample plots on one ridge over the 19 years since BWA was first detected there. Overall forest growth after 2007 could indicate partial recovery, a momentary pause in BWA invasion, or tree growth after severe weather events (Hutton 2015).

Ranges of Trees at Risk

Many of the host trees of these two pests are widespread; others are more narrowly endemic.

Limber pine reaches from Alberta and British Columbia south to mountain peaks in Arizona and New Mexico. Whitebark pine is found from Alberta and British Columbia to California and Nevada (USDA Plants database. Subalpine fir stretches from southeast Alaska along the Canadian Rockies coast into Washington, Oregon, east into Idaho, Montana, Wyoming, Colorado, Utah, even into scattered mountain ranges of Nevada and New Mexico (Hutton 2015).

Limber pine and subalpine fir are also found in a wide range of ecosystems within these ranges. Limber pine is found at both upper and lower tree lines in grassy, open forests; on exposed rocky slopes; and in dense, mixed-conifer stands. Subalpine fir is a pioneer species on ridges, alpine meadows, avalanche chutes, and lava beds (Ragenovich and Mitchell, 2006).

Before arrival of non-native pests or pathogens, these tree species have persisted for thousands of years under harsh conditions (Hutton 2015). Many of the individual trees were long-lived; some five-needle pines, e.g., bristlecone pines, have famously live for thousands of years. Core studies demonstrated that subalpine firs trees could live 272 years in the forests of Olympic National Park and 240 years in Glacier National Park (Hutton 2015). Surely loss of these trees – or even their conversion from large and old to small and short-lived – will result in significant destruction of these unique biomes.

All these trees play important roles in high altitude, unique ecosystems (Pederson et al. no date; Dawe 2020; Hutton 2015):

They retain ground water, slow the rate of snow melt, and maintain stream flow characteristics and water quality;
They curtail soil erosion and maintain slope stability; and
They provide high-value food and shelter to wildlife.

Whitebark and limber pines are famous for providing critical food for many wildlife species at high elevations —notably bears and nutcrackers (Compendium and Dawe 2020).

More Pest Threats

Other diseases, insects, and disturbances also pose serious threats to these tree species. The threats vary by region and age of the stand. They include – for the pines — mountain pine beetle (Dendroctonus ponderosae), dwarf mistletoe (Arceuthobium spp.), and various shoot, cone or foliage insects and pathogens. For subalpine fir, threats include western balsam bark beetle (Dryocoetes confusus), fir engraver (Scolytus ventralis), and the fir root bark beetle (Pseudohylesinus granulatus) (Hutton 2015). Trees are also damaged by bear and deer, seed predation by squirrels, wildfire, and biotic succession.

On Washington’s Olympic Peninsula, BWA initiates or predisposes subalpine fir for a novel disturbance complex. BWA-caused stress makes the trees more susceptible to moisture stress and endemic bark beetle attack. Surviving trees are subsequently subject to toppling by wind. A tree can die in a few years, survive with insects for up to 20 years, or recover, depending on duration, severity, and location of infestation, and local environmental conditions (Hutton 2015).

BWA study plots in the Cascade Range experienced subalpine fir mortality ranging from 7 to 79% (measured as stem counts, not basal area) over a 19 to 38 years study period. Higher mortality occurred at low-elevation, mesic sites. One stand experienced 40% mortality in 19 years, but lost the remaining 60% during a subsequent spruce budworm infestation. Most plots continued to show sporadic signs of adelgid presence and continued tree mortality. However, 41-69% of trees survived stem infestations (Hutton 2015).

How to Protect These Ecosystems

The seeds of both whitebark and limber pines are dispersed to newly disturbed, open areas by Clark’s nutcracker (Nucifraga columbiana). Furthermore, whitebark cones open to release seeds only after fire. This had led to expectations that prescribed fire could promote regeneration of these species. However, studies by Dawe (2020) and other have found that nutcracker seed caching behavior and seedling establishment are complex. Fire management might have to vary among regions, demanding consideration of stand characteristics,like openness and the presence of other tree species. For example, in the Colorado Front Range, limber pine can be replaced by subalpine fir when fire-free intervals are long. On the other hand, in Alberta, fire appeared to boost regeneration of the dominant tree species in the stands pre-fire. In the study areas, these were white spruce (Picea glauca) and lodgepole pine (Pinus contorta) (Dawe 2020). Dawe recommends protecting existing stands of limber pine through fire mitigation efforts, e.g., thinning and other fuel treatments, and supplementary planting of seedlings.

Efforts to find biocontrol agents to target the balsam woolly adelgid began in 1957; the original focus was on the insects’ damage to Fraser fir (Abies fraseri) in the southern Appalachians. More than 25 predatory species have been introduced from Europe and Asia. There was simultaneous research on native predators. None has had an impact on BWA populations in either the East or the West.

Neither white pine blister rust nor balsam woolly adelgid is considered a quarantine pest by federal officials, so there is no attempt to prevent their movement via interstate trade in Christmas trees, timber, or nursery stock. Hutton (2015) hypothesizes that the absence of regulatory measures targetting BWA arises from the pest’s gradual effect and the hosts’ not being commercially important as timber species (although several firs are important in horticulture and as Christmas trees). I think another factor is that the pests were introduced so long ago and are now widespread.

Efforts are under way to detect resistant genotypes to be used in breeding programs. Several of the lower-elevation five-needle pines vulnerable to WPBR have benefitted from extensive breeding efforts Whitebark pine has more recently been added to programs.

The eastern Fraser fir is the target of breeding – primarily for Christmas trees (APS). However, at least small-scale volunteer efforts have been carried forward by the Alliance for Saving Threatened Forests.

Hutton (2015) expresses hope that evolutionary pressure by BWA might enhance survival of more resistant forms of subalpine fir and lead to their gradual takeover. However, I ask, why leave it to chance?

In this context, I remind you of my involvement with a group (see Bonello et al. 2019) proposing creation of a federal Center for Forest Pest Control and Prevention to implement end-to-end responses to forest pest invasions – including overcoming the currently inadequate focus on detection, development and deployment of genetic resistance using modern techniques that allow for much faster breeding cycles.

I am puzzled that the Project CAPTURE places whitebark pine and subalpine fir only in Class A4.2, not among the highest priority species (Potter et al. 2019). As I blogged last spring, Project CAPTURE is part of a multi-partner effort to categorize and prioritize US tree species for conservation actions based on the threats and the trees’ ability to adapt to those threats. I find it puzzling because I am not sure I agree that these two species have a moderately high mean pest severity score – as required by the category. I am less puzzled by the assignment of a low adaptive capacity score.

Limber pine apparently ranks even lower in the Project CAPTURE priority process.

Posted by Faith Campbell

SOURCES

A comprehensive review and synthesis of the history, ecology, and management of white pines threatened by white pine blister rust see the August 2010 issue of Forest Pathology (Vol. 40:3-4).

American Phytopathological Society. Science Daily. December 9, 2019 https://www.sciencedaily.com/releases/2019/12/191209161314.htm?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+sciencedaily%2Fplants_animals%2Finvasive_species+%28Invasive+Species+News+–+ScienceDaily%29

Dawe, D.A., V.S. Peters, M.D. Flannigan. 2020. Post-fire regeneration of endangered limber pine (Pinus flexilis) at the Northern extent of its range. Forest Ecology and Management 457 (2020) 117725

Hutton, K.M. 2015. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy. University of Washington. Available here

Morin, R. Presentation to the 81^st Northeastern Forest Pest Council Northeastern states forst agencies, Philadelphia, Pennsylvania, March 2019.

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S. 2019. Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest P&P threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/

Ragenovich, I.R. and R.G. Mitchell. 2006. Forest Insect and Disease Leaflet (FIDL) #118. http://www.na.fs.fed.us/pubs/fidls/bwa.pdf

Sniezko, R.A., M.F. Mahalovich, A.W. Schoettle, D.R. Vogler. 2011. Past and Current Investigations of the Genetic Resistance to Cronartium ribicola in High-elevation Five-needle Pines. In Keane, R.F., D.F. Tomback, M.P. Murray, and C.M Smith, eds. 2011. The future of high-elevation, five-needle white pines in Western North America. Proceedings of the High Five Symposium. 28-30 June, 2010. Missoula, MT.

International Year of Plant Health: Time to Admit that the International Phytosanitary System is Failing

As I noted last November, the premise of the international phytosanitary system – the Agreement on the Application of Sanitary and Phytosanitary Standards (SPS Agreement) and the International Plant Protection Convention (IPPC) – is that importing countries should, and can, rely on exporting countries to take the actions necessary to meet the importing countries’ plant health goals. However, the experience with the International Standard on Phytosanitary Measures (ISPM) #15 and wood packaging casts doubt on this premise.

Exporters are not reliably ensuring the cleanliness of their wood packaging, putting American forests at risk. Indeed, some experts have concluded that continuing to implement ISPM#15 at current levels could triple the number of non-native wood-boring insects introduced into the U.S. by 2050 (Leung et al. 2014).

Too many shipments carry wood packaging that bears no ISPM#15 stamp. And too many pieces of wood packaging arrive with the ISPM#15 stamp, yet are not reliably pest-free. If we cannot clean up this pathway – which involves boards or even logs that are, after all, already dead — it bodes poorly for limiting pests imported with other commodities that are pathways for tree-killing pests – especially living plants (plants for planting). Living plants are much more easily damaged or killed by treatments than the dead wood used in packaging – so ensuring pest-free status of a shipment is even more difficult. (A longer discussion of the SPS Agreement and IPPC is found in Chapter III of Fading Forests II, available here.

Here are the problems – and the latest evidence.

ALB larva in piece of wood packaging material

Too Many Shipments with Pest-Infested Wood Packaging Are Reaching the Country

My information on Customs and Border Protection (CBP) interceptions comes primarily from Kevin Harriger (see full reference at end of the blog). I will note when it comes from other sources.

In November 2019, Kevin Harriger reported that over the past three years, CBP detected a regulated pest, on average, in 30% of the wood packaging the agency intercepted because it was not compliant with ISPM#15. Non-compliance is defined as wood packaging that either lacks an official mark or is infested by a quarantine pest, or both.

From this and previous reports, I have 10 years of CBP interception data – from 2020 – 2019. These data thus begin four years after the U.S. began implementing ISPM#15 (in 2006) and 11 years after the U.S. began requiring China to treat wood packaging accompanying its exports (in 1999).

Over the period 2010 – 2018, CBP intercepted an average of 3,183 shipments with non-compliant wood packaging each year. On average, 2,100 (66%) of these shipments lacked the required ISPM#15 mark. A live quarantine pest was found in an average of 794 (25%) shipments. (There was some overlap in the categories).

In 2019, CBP intercepted a total of 2,572 non-compliant shipments (Stephen Brady, CBP, April 2020). Those lacking the ISPM#15 mark number 1,825 (71%). Shipments in which a live pest was found numbered 747 (29%).

The 2019 data show decreases, in absolute numbers, from earlier years in all categories: a 19% decrease below 1010-2018 average of shipments intercepted; a 13% decrease in number of shipments intercepted because the wood packaging lacked the ISPM#15 mark; a decrease of 6% in the number of shipments intercepted that had a quarantine pest. It is too early to say whether CBP’s stronger enforcement approach launched in November 2017 has resulted in a lower number of shipments in violation of ISPM#15 approaching our shores.

There has been a dispute about which categories of packaging are most likely to be infested. The categories are pallets, crates, spools for cable, and dunnage (wood used to brace cargo and prevent it from shifting). The CBP data available to me and the study by Krishnankutty et al. (2020b – see full reference at the end of this blog) shed no light on that issue.

What is the actual number of infested containers approaching our shores? We know that CBP inspects, on average, 2% of incoming containers – so the above interception data reflect a small percentage of probable true approach rate.

The first issue is, how many containers arrive here?

I have been unable to find data for 2019 – much less 2020, when the media report that import volumes have crashed. Until recently, import volumes had been rising. According to a U.S. DOT report to Congress (see reference at the end of this blog), 25 U.S. maritime ports received 24,789,000 loaded shipping containers (measured as TEU – 20-foot equivalent) in 2018. The number of incoming containers had increased at the top three ports – Long Beach, Los Angeles, and New York / New Jersey – between 3% and 7% since 2016.

However, APHIS told me in November 2019 that CBP reports that only about 13 million loaded containers enter the country every year by rail, truck, air, or sea. While I can’t yet explain the discrepancy, one possible explanation is that DoT counts 40-foot containers as two 20-foot containers.

(Of course, pests introduced to Canada also threaten North America’s forests. Canada received fewer than 5 million containers via maritime trade in 2016 (Asbil pers. comm. 2018).

Two decade-old estimates of the proportion of incoming containers that hold wood packaging (Haack et al. 2017, Meissner et al. 2009) allow me to estimate the risk associated with these incoming containers. Meissner et al. found that 75% of maritime containers have wood packaging. Haack et al. estimated that the wood in 0.1% of those containers was infested. Applying these two factors, I conclude that as many as 18,590 of incoming containers in maritime trade could have been transporting a woodborer in the regulated families (Cerambycids, Buprestids, Siricids). I am hesitant to apply the calculation to CBP’s estimate because I don’t know how many of the 13 million containers entered by sea. However, if I assume that the same percentage of wood packaging applied to all the CBP-counted containers, I conclude that 9,750 of those containers held infested wood packaging – still a significant number.

The actual approach rate might be less – or more! Haack et al. (2014) did not include imports from China in their calculations. Given the history of interceptions, it appears probable to me that a recalculation of the approach rate that included China would probably raise the overall proportion.

Furthermore, 11 years have passed since Haack and Meissner made their calculations. During that time, ISPM#15 has been amended to make it more effective. The most important change was restricting the size of bark remnants that may remain on the wood. I have asked several times that APHIS commission a new analysis of Agriculture Quarantine Inspection Monitoring data to determine the pest approach rate before and after the CBP action in order to determine whether the more aggressive enforcement has led to reductions in non-compliant shipments at the border.

By comparing Dr. Haack’s estimate (see above) with the CBP data, I estimate that Customs is detecting and halting the importation of 4 – 8% of the shipments that actually contain pest-infested wood. Since CBP inspects only about two percent of incoming shipments, the higher detection rate demonstrates the value of CBP’s program to target likely violators – and deserves praise. But it is obviously too low a “catch” rate to provide an adequate level of protection for our forests.

ISPS#15 Is Not Helping to Target Inspections

So – ISPM#15 still allows too many pests to arrive at our shores. Is ISPM#15 at least helping phytosanitary agencies target inspections? No, because both U.S. and European data demonstrate that a high proportion of shipments containing infested wood pieces bore the ISPM#15 stamp. Phytosanitary agencies cannot rely on the presence or absence of the stamp to indicate the pest risk level.

U.S. data:

During the period 2010-2015, CBP found that an average of 95% of pest-infested shipments bore the ISPM#15 mark (Harriger). Unfortunately, CBP data from more recent years don’t provide this breakdown.
In the past two years, CBP inspectors have repeatedly found pests in dunnage bearing the ISPM#15 mark.
Krishnankutty et al. (2020b) analyzed wood packaging from 42 countries of origin intercepted by CBP over six years (April 2012 – January 2018). They found that 87% of the interceptions bore the ISPM mark.

I blogged earlier about the velvet longhorned beetle (Trichoferus (=Hesperophanes) campestris) This pest, like others, has reached our shores and entered the country both before and after implementation of ISPM#15. The predictable result is that VLB is established in three states and has been detected in 14 others plus Puerto Rico (Krishnankutty, et al. 2020a). Apparently we have been lucky that this one isn’t as damaging as so many are!

European data:

For Europe, see Eyre et al. (2018). They concluded that the ISPM-15 mark was of little value in predicting whether harmful organisms were present.

This is alarming and we need to understand the reason – How much is caused by fraud? How much is caused by failure of treatment – either intrinsic weakness or incorrect application? APHIS researchers have found that larvae from wood subjected to methyl bromide fumigationwere more likely to survive to adulthood than those intercepted in wood that had been heat treated (Nadel et al. 2016).

Krishnankutty et al. (2020b) query whether the 2009 requirement that wood be debarked might be less effective in countering insect species that require bark only in the early stages of larval development. Half of the species intercepted in hardwood shipments (e.g., Anoplophora glabripennis, Phoracantha recurva) might fit this profile. They also appear to pose a higher threat since they are polyphagous and known to infest healthy hosts. While some of the softwood-inhabiting species also require bark, they not known to infest living trees and only a quarter were classified in the high-risk group. The Mech et al. 2020 finding that no wood-borers that specialize in conifers posed a high risk appears to support these different impacts.

Krishnankutty, et al. (2020b) also note the risk from pallet recycling. The wood might occasionally be infested by dry-wood borers. One puzzling example was wood packaging shipped from Brazil and bearing a Brazilian ISPM#15 stamp that was infested with a larva of T. campestris (VLB). This is an Asian species not recorded as being present in South or Central America. The authors speculate that the pallets were recycled in Brazil after inadequate treatment in their original places of manufacture.

Of the 17 wood borer species intercepted in hardwoods, three have reproducing populations in the U.S.: A. glabripennis, Phoracantha recurva and T. campestris. Krishnankutty et al. (2020b) say that they are unaware of any of the non-native buprestids and siricids intercepted in softwood SWPM being established in the US. (One Siricid that is established, Sirex noctillio, was not detected in the wood packaging analyzed in this study.)

What Can Be Done to Slow or Eliminate this Pathway?

CBP strengthened enforcement of ISPM#15 in November 2017. CBP’s enforcement actions increased by 400% from 2017 to 2018 (John Sagle, CBP, pers. comm). CBP has also expanded its outreach to shippers and others involved in international trade with the goal of reducing all types of non-compliance – lack of documentation, pest presence, etc. in both wood packaging and shipping containers. The outreach includes awareness campaigns targetting trade, industry, affiliated associations, CBP employees, and international partners (Harriger).

Certain countries have a long-standing record of non-compliance with ISPM#15 – as seen in interception records.

Haack et al. 2014 – Italy was the country of origin for most wood borers intercepted 1985 – 2000.
Haack et al. 2014 – the top 5 countries in the 2003 – 2009 period were Mexico (33.7%), Italy (14.2%), Canada (13.4%), Netherlands (4.4%), China (4.1%).
APHIS’ interception database for FY2011-2016 (provided to me) showed Mexico, China, Italy, and Costa Rica had the highest numbers of interceptions.
Krishnankutty et al. (2020b) found the highest numbers of interceptions came from Mexico, China, and Turkey.

These numbers reflect in part the huge volumes of goods imported from both Mexico and China. But China and Italy stand out for their poor performance. (The U.S. does not regulate – or inspect! – wood packaging from our third-largest trade partner Canada.)

Officials know which individual companies within these countries have a history of non-compliance. For example, 21 of the interceptions on wood packaging made from Populus trees in China (53%) were associated with stone, ceramic, and terracotta commodities. Anoplophora glabripennis was intercepted six times in Populus originating from a single wood-treatment facility in China (Krishnankutty et al. 2020b).

How reduce risk to U.S. forests?

Over the past year or two, I have suggested the following actions:

USDA APHIS join Bureau of Customs and Border Protection in penalizing violators.
Citing the need for setting a higher “level of protection”, APHIS & the Canadian Food Inspection Agency (CFIA) should prepare a risk assessment to justify adopting more restrictive regulations. The new regulations should prohibit use of packaging made from solid wood – at least from the countries with records of high levels of non-compliance (listed above).
USDA Foreign Agriculture Service (FAS) should assist U.S. importers to determine which suppliers reliably provide compliant wood packaging.
USDA FAS and APHIS should help importers convey their complaints about specific shipments to the exporting countries’ National Plant Protection Organizations (NPPOs; departments of agriculture).
APHIS should increase pressure on foreign NPPOs and the International Plant Protection Convention more generally to ascertain the reasons ISPM#15 is failing and to fix the problems.
APHIS should fund more studies and audits of wood packaging to document the current efficacy of the standard, including an urgent update of the Haack study of pest approach rate.

The international standard has demonstrably failed to provide a secure method to evaluate the pest risk associated with wood packaging accompanying any particular shipment. The presence of the stamp on pieces of wood packaging does not reliably show that the wood is pest-free.

The situation is even worse re: movement of plants for planting.

SOURCES

Asbil, W. Canadian Food Inspection Agency, pers. comm. August 2018.

Eyre, D., R. Macarthur, R.A. Haack, Y. Lu, and H. Krehan. 2018. Variation in Inspection Efficacy by Member States of SWPM Entering EU. Journal of Economic Entomology, 111(2), 2018, 707–715)

Haack, R. A., K. O. Britton, E. G. Brockerhoff, J. F. Cavey, L. J. Garrett, M. Kimberley, F. Lowenstein, A. Nuding, L. J. Olson, J. Turner, and K. N. Vasilaky. 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:e96611.

Harriger, K. Executive Director for the Agriculture Programs and Trade Liaison office, Department of Homeland Security Bureau of Customs and Border Protection (CBP), presentations to the Continental Dialogue on Non-Native Forest Insects and Diseases, over appropriate years. https://continentalforestdialogue.org/events/

Krishnankutty, S.M., K. Bigsby, J. Hastings, Y. Takeuchi, Y. Wu, S.W. Lingafelter, H. Nadel, S.W. Myers, and A.M. Ray. 2020a. Predicting Establishment Potential of an Invasive Wood-Boring Beetle, Trichoferus campestris (Coleoptera:) in the United States. Annals of the Entomological Society of America, XX(X), 2020, 1–12

Krishnankutty, S., H. Nadel, A.M. Taylor, M.C. Wiemann, Y. Wu, S.W. Lingafelter, S.W. Myers, and A.M. Ray. 2020b. Identification of Tree Genera Used in the Construction of Solid Wood-Packaging Materials That Arrived at U.S. Ports Infested With Live Wood-Boring Insects. Commodity Treatment and Quarantine Entomology

Leung, B., M.R. Springborn, J.A. Turner, E.G. Brockerhoff. 2014. Pathway-level risk analysis: the net present value of an invasive species policy in the US. The Ecological Society of America. Frontiers of Ecology.org

Mech, A.M., K.A. Thomas, T.D. Marsico, D.A. Herms, C.R. Allen, M.P. Ayres, K.J. K. Gandhi, J. Gurevitch, N.P. Havill, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, A.N. Schulz, D.R. Uden, & P.C. Tobin. 2019. Evolutionary history predicts high-impact invasions by herbivorous insects. Ecol Evol. 2019 Nov; 9(21): 12216–12230.

Meissner, H., A. Lemay, C. Bertone, K. Schwartzburg, L. Ferguson, L. Newton. 2009. Evaluation of Pathways for Exotic Plant Pest Movement into and within the Greater Caribbean Region. Caribbean Invasive Species Working Group (CISWG) and USDA APHIS Plant Epidemiology and Risk Analysis Laboratory

Nadel, H. S. Meyers, J. Molongoski, Y. Wu, S. Lingafelter, A. Ray, S. Krishnankutty, A. Taylor. 2017. Identification of Port Interceptions in Wood Packing Material Cumulative Progress Report, April 2012 – June 2017

USDA APHIS interception database – pers. comm. January 2017.

USDA APHIS press release dated September 12, 2018

U.S. Department of Agriculture, Press Release No. 0133.20, January 27, 2020

US Department of Transportation. Port Performance Freight Statistics in 2018 Annual Report to Congress 2019 https://rosap.ntl.bts.gov/view/dot/43525

Wu, Y., S.M. Krishnankutty, K.A. Vieira, B. Wang. 2020. Invasion of Trichoferus campestris (Coleoptera: Cerambycidae) into the United States characterized by high levels of genetic diversity and recurrent intros. Biological Invasions Volume 22, pages1309–1323(2020)

Yemshanov, D., F.H. Koch, M. Ducey, K. Koehler. 2012. Trade-associated pathways of alien forest insect entries in Canada. Biol Invasions (2012) 14:797–812

Posted by Faith Campbell

Non-Native Pests on North American Conifers: New Overview

Fraser fir killed by balsam woolly adeligid
Clingman’s Dome, Tennessee

A recent study provides an overview of the threat non-native insects pose to conifers in North America. Unfortunately, pathogens are not included in the study. I provide a citation to the study (Mech et al., 2019) at the end of this blog.

The study’s authors based their analysis on 58 insects that specialize on conifers (trees in the families Cupressaceae, Pinaceae, and/or Taxaceae). These were derived from a list of over 500 herbivorous insects identified by Aukema et al. (2010) and Yamanaka et al. (2015). Mech and colleagues determined that of the approximately 100 conifer species native to North America, 49 have been colonized by one or more of these 58 non-native insects. Three-quarters of the affected trees have been attacked by more than one non-native insect. One tree species was attacked by 21 non-native insects.

Looked at from the opposite perspective, one of the insects attacked 16 novel North American hosts.

Of these 58 insects, only six are causing high impacts, all in the orders Hymenoptera (i.e., sawflies) and Hemiptera (i.e., adelgids, aphids, and scales). (“High impact” is defined as causing mortality in the localized host population, recognizing potential spread.)

These six are (1) Adelges piceae—balsam woolly adelgid; (2) Adelges tsugae—hemlock woolly adelgid; (3) Elatobium abietinum—green spruce aphid; (4) Gilpinia hercyniae—European spruce sawfly; (5) Matsucoccus matsumurae—red pine scale; and (6) Pristiphora erichsonii—larch sawfly. The high-impact pests included no wood borers, root feeders, or gall makers.

Mech and colleagues analyzed these relationships in an effort to determine factors driving bioinvaders’ impacts. They evaluated the probability of a non-native conifer specialist insect causing high impact on a novel North American host as a function of the following: (a) evolutionary divergence time between native and novel hosts; (b) life history traits of the novel host; (c) evolutionary relationship of the non-native insect to native insects that have coevolved with the shared North American host; and/or (d) the life history traits of the non-native insect.

They found that the major drivers of impact severity for those that feed on foliage and sap (remember, they did not evaluate other feeding guilds) were:

1) Host’s evolutionary history – Divergence time in millions of years (mya) since North American species diverged from a coevolved host of the insect in its native range. The greatest probability of high impact for a leaf-feeding specialist was on a novel conifer that diverged from the native conifer host recently (~1.5–5 mya). The divergence time for peak impact was longer for sap‐feeders (~12–17 mya). The predictive power of the divergence-time factor was stronger for sap-feeders than for leaf feeders.

2) Shade tolerance and drought intolerance – A tree species with greater shade tolerance and lower drought tolerance is more vulnerable to severe impacts. This profile fits most species of Abies, Picea, and Tsuga. On the other hand, novel hosts with low shade tolerance and higher drought tolerance had a very low likelihood of suffering severe impacts.

a bad infestation of hemlock woolly adelgid

3) Insect evolutionary history – When a non-native insect shares a host with a closely related herbivore native to North America, the invader is less likely to cause severe impacts. However, this factor in isolation had relatively poor predictive performance.

None of the insect life history traits examined, singly or in combination, had predictive value. The traits evaluated were feeding guild, native region, pest status in native range, number of native host genera, voltinism (frequency of egg-laying periods), reproductive strategy, fecundity, and/or mechanism of dispersal.

See Mech et al. (2019) for a discussion of hypotheses that might explain these findings.

My Questions Answered!

The authors inform me that their project will eventually include introduced insects attacking all kinds of trees. The more than 500 insect species that utilize woody hosts have been placed into one of three categories: 1) conifer specialist (only utilizes conifer hosts), 2) hardwood/woody angiosperm specialist (only utilizes hosts in a single angiosperm family), or 3) generalists (utilizes hosts in more than one angiosperm family or both angiosperms and conifers) (Mech pers. comm.) They began with the smallest group – the conifer specialists – so that they could more easily work out kinks in their procedures.

I had asked why the brown spruce longhorned beetle (Tetropium fuscum) – which is established in Nova Scotia – was not included in this study. According to the authors, this cerambycid beetle has been reported to feed occasionally on hardwood species, so it has been placed in the third group.noted above.

SOURCES

Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, & S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. Bioscience. December 2010 / Vol. 60 No. 11

Yamanaka, T., Morimoto, N. , Nishida, G. M. , Kiritani, K. , Moriya, S. , & Liebhold, A. M. (2015). Comparison of insect invasions in North America, Japan and their Islands. Biological Invasions, 17, 3049–3061. 10.1007/s10530-015-0935-y [CrossRef] [Google Scholar]

Posted by Faith Campbell

What the VLB Saga Tells Us About Detection Surveys

Setting Priorities for Surveillance

CBP inspects a pallet suspected for harboring an insect pest

Despite Customs and Border Protection’s heroic efforts to target inspection of wood packaging shipments, based on histories of non-compliance of specific importers’ wood packaging (which I have often praised), the majority of larvae occurring in wood packaging would probably not be intercepted by inspectors. Instead, they would be transported to the cargo’s intended destinations (Wu et al. 2020). I described these problems in the preceding blog about the velvet longhorned beetle (VLB).

As I have noted in the past, CBD detects an average of 800 shipments per year with non-compliant wood packaging. That figure is less than five percent of the 16,500 infested shipping containers that might enter the country each year, based on the estimate by Haack et al., (2014) that one tenth of one percent of incoming wood packaging might be infected.

So there is always a need to improve surveillance for pests that inspection fails to catch. We can do that in at least the following ways:

1) better target detection efforts on the most likely areas where a pest might establish

2) improve collection and use of pest-related information to determine probable hosts, pathways of movement, and potential impacts.

Discovering How the Pest Moves

Sometimes improvements must be linked to individual species – although assisted by knowledge about species with similar life histories, e.g., similar hosts or flight periods or about its close relatives (see Ray’s development of a VLB lure; full citation at end of this blog).

Other times, improvements might result from more generalizable adjustments.

For example, the pathway analysis undertaken by Krishnankutty and colleagues is one approach to improving geographic targetting. They analyzed aspects of the velvet longhorned beetle’s pathways of introduction: 1) the types of imports associated with VLB-infested wood packaging; 2) ports where the beetle has been detected in recent years; plus 3) the presence and calculated probable volume of imports for the types of commercial operations considered likely to transport the beetle.

This analysis required access to detailed data from many sources. They included 1) interception data revealing the types of products most often associated with infested wood and the intended destinations of intercepted cargoes; 2) the North American Industry Classification System data listing locations of businesses likely to utilize these products; 3) the beetle’s climatic requirements; and 4) the locations of actual detections of VLB as revealed by Cooperative Agricultural Pest Survey (CAPS) and other trapping programs.

Approaches to Learning More

Relying on traps to detect new pests has several advantages. These include the relative ease of scaling up to larger areas, and – sometimes — the ability to use general lures that attract a variety of insects. Some insects are attracted only, or primarily, to specific lures. Labor intensiveness (and expense) varies with how many traps must be deployed, whether the sites are easily accessible, difficulty extracting trapped insects, and the difficulty sorting the dead insects to find the species of interest.

A second approach is more labor-intensive and expensive, but it gives more information on the target species. This approach is to rear intercepted insect larvae in logs inside containers (to prevent escape) until they reach maturity and emerge. This approach facilitates determination of the species (it is difficult to identify larvae) … and allows an evaluation of feeding behavior – which translates into assessment of the damage caused to the tree.

The Canadian Food Inspection Agency (CFIA) began applying this survey method in 2006. CFIA collects logs from trees in declining health at high risk sites, such as industrial zones, current and historic landfills, and disposal facilities where large volumes of international wood packaging and dunnage are stored for extended periods of time. The logs are obtained from trees removed as part of municipal hazard tree removal programs. CFIA takes the logs to one of four research laboratories (in Toronto, Nova Scotia, Montreal, and North Vancouver), where they are placed in rearing chambers and allowed time to see what insects emerge. The logs are also dissected to reveal the type of damage caused by the insects – that is, determine whether insect was cause of tree mortality [Bullas-Appleton et al. 2014) .

The United States is applying the same approach, but less systematically.

APHIS developed a short-term project aimed at addressing two challenges: identifying larvae found in wood packaging to the species level (larvae intercepted at the border are often identified only to family); and gaining valuable information about the failure of currently required phytosanitary treatments as regards particular genera and species.

In a cooperative project begun in 2012, the DHS Bureau of Customs and Border Protection (CBP) collected live larvae of Cerambycidae and Buprestidae (and, since September of 2015, Siricidae), intercepted during inspection at initially six, later 11 U.S. ports.

mesh bags in which APHIS is rearing larvae obtained from wood packaging inspected by CBD at ports of entry
photo by USDA APHIS

These larvae were sent to an APHIS containment facility where many were reared to adults. Upon emergence, adult specimens were killed and identified by experts working for the National Identification Service. DNA barcodes of dead larvae and the reared adults were defined and compared and any new information was added to public genetic databases. These DNA barcodes have enhanced the capacity of anyone involved in pest interception and detection to rapidly identify larval stages. In 2017, APHIS determined that it had detected almost the full range of species that might be transported in wood packaging, and stopped funding the project.

As of June 2017, the APHIS project had received 1,289 intercepted wood borers (1,052 cerambycids, 192 buprestids and 45 siricids) from 45 countries (See Nadel et. al 2017). The extensive analysis of velvet longhorned beetle described in my previous blog link was greatly assisted by the resulting data.

Cerambycid larva which was part of the study
photo USDA APHIS

Years before the APHIS project, USDA Forest Service wanted to try applying rearing techniques to aid early detection of insects in the country. At first, the scientists asked residents of Washington, D.C. to identify street trees that appeared to be infested with pests. Those trees were then cut and sections placed in rearing containers to allow scientists to determine what was causing the problem (Harvard Science).

The project was transferred in 2015 to Boston and New York. The Boston location is an arboretum; the advantage of this site is that it has 1) a diversity of tree species; 2) trained staff; and 3) detailed records of most trees on-site (Harvard Science). Project scientists now accept material from stressed, diseased, or dying trees. This material is loaded into sealed barrels and allowed two years for insects to emerge. Since 2015, project scientists have examined 8,605 beetles comprising 223 species. These studies have resulted in 16 new state records, records of some Scolytinae that are rarely collected from traditional trapping methods; documentation of new host associations; and discovery of one previously undescribed species — Agrilus sp. 9895 (See DiGirolomo, Bohne and Dodds, 2019).

SOURCES

Bullas-Appleton, E., T. Kimoto, J.J. Turgeon. 2014. Discovery of Trichoferus campestris (Coleoptera: Cerambycidae) in Ontario, Canada and first host record in North America. Can. Entomol. 146: 111–116 (2014).

Marc DiGirolomo, Michael Bohne, Kevin Dodds. 2019. Presentation to the 19^th Annual Meeting of the Continental Dialogue on Non-Native Forest Insects and Diseases https://continentalforestdialogue.files.wordpress.com/2019/12/bohne.continentaldialogue1.pdf USFS – Durham, NH – 19^th Dialogue meeting

Haack, R. A. 2006. Exotic bark- and wood-boring Coleoptera in the United States: recent establishments and interceptions. Can. J. For. Res. 36: 269–288.

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

Krishnankutty, S.M., K. Bigsby, J. Hastings, Y. Takeuchi, Y. Wu, S.W. Lingafelter, H. Nadel, S.W. Myers, and A.M. Ray. 2020. Predicting Establishment Potential of an Invasive Wood-Boring Beetle, Trichoferus campestris (Coleoptera: Cerambycidae) in the United States. Annals of the Entomological Society of America, 113(2), 2020, 88-99. https://doi.org/10.1093/aesa/saz051

Ray, A.M., J. Francese, Y. Zou, K. Watson, D.J Crook, and J.G. Millar. 2019. Isolation and identification of a male-produced aggregation sex pheromone for the velvet longhorned beetle, Trichoferus campestris. Scientific Reports 2019. 9:4459. https://doi.org/10.1038/s41598-019-41047-x

Posted by Faith Campbell

Have we dodged a bullet? (more like a burst of fire from a submachine gun)

Cerambycid larva detected in wood packaging
photo by Oregon Department of Agriculture

Many highly damaging wood-borers have been introduced to North America in wood packaging.

One woodborer, a beetle in the Cerambycidae, has been introduced multiple times to the United States — both before and after implementation of ISPM#15, the international regulations designed to stop such introductions. This is the velvet longhorned beetle (VLB) (Trichoferus (=Hesperophanes) campestris). Independent scientists have recently documented how VLB is introduced and where it is established.

I first blogged about the VLB three years ago. At that time, I asked why APHIS had not undertaken a quarantine and other actions to contain or eradicate the beetle, which was clearly established in an orchard in Utah (Wu et al. 2020; full source citations appear at the end of the blog). Now, the VLB is established in three states and has been detected in many more (details below).

It appears that the VLB will not cause significant damage. I hope this proves true, because it is certainly travelling here on a regular basis. While the most detailed study of the VLB’s potential impact in North America is not yet complete, early indications are that the beetle attacks mostly dying or dead trees.

A Widespread and Adaptable Pest

The VLB is native to China, Central Asia, Japan, Korea, Mongolia, and Russia. It has also been recorded in several European countries. The risk of introduction is broader, however. VLB has established throughout the Middle East and Europe, as well as parts of South and Central America. U.S. officials have intercepted live VLB individuals in shipments originating from these introduced populations, i.e., Brazil, Italy, Mexico, and Spain (Ray et al. 2019).

Wu et al. (2020) studied the genetic diversity of VLB specimens collected by in the United States by 1) trapping at several locations and 2) by testing those intercepted in wood packaging at U.S. ports. The scientists found high levels of diversity between and even within each limited geographic population. These results indicate that VLB has been introduced numerous times via the wood packaging pathway. They also found some evidence that introduced VLB populations might be expanding so it is important to understand pathways of spread within the country (Wu et al. 2020).

Where VLB is in the United States

The VLB is now officially considered to be established in Cook and DuPage counties, IL; Salt Lake County, UT; and Milwaukee, WI. [Krishnankutty et al. 2020).

However, adults have been detected in 26 counties in 13 additional states, plus Puerto Rico, since 1992. Since a trapping survey for woodborers began in 1999, this joint federal and state Cooperative Agricultural Pest Survey (CAPS) has trapped VLB in Colorado (2013), Illinois (2009), New Jersey (2007, 2013), New York (2014, 2016–2018), Ohio (2009, 2017–2019), Pennsylvania (2016), Rhode Island (2006), and Utah (2010, 2012–2019). (Krishnankutty et al. 2020). Also, Oregon detected VLB in 2019 (Oregon Department of Agriculture 2019).

Interceptions in Wood Packaging

The velvet longhorned beetle has been detected frequently in wood packaging since at least the middle 1980s (when APHIS began recording interceptions) (Haack 2006). (Haack’s study covered 1985-2000, before implementation of the International Standard on Phytosanitary Measures (ISPM) #15.)

APHIS’ official interception database listed 60 separate interceptions of VLB in the more recent ten plus-year period June 1997 – November 2017 – which overlaps pre- and post-implementation of ISPM#15. Eighty-eight percent of these interceptions were in wood packaging. Seven percent were in wood products. The remaining seven percent were in passenger baggage or unidentified products.

As has been the case generally since ISPM#15 was adopted, a high percentage — 65.4% — of the intercepted wood packaging during this period bore the mark certifying compliance with the ISPM#15 treatment requirements. Unsurprisingly, China was the origin of 81.6% of the intercepted shipments infested by pests (Krishnankutty et al. 2020).

In the most recent data studied, all from the period after implementation of ISPM#15 — 2012 – 2017, 28 VLB were found in analyses of a sample of wood packaging (Nadel et al. 2017). (I will discuss this study and other detection tools in a separate blog.)

In agreement with earlier findings, the most high-risk imports were determined to be wood packaging for stone, cement, ceramic tile, metal, machinery, manufactured wood products (furniture, decorative items, new pallets, etc.), and wood-processing facilities (Krishnankutty et al. 2020).

These findings largely confirm what we already know about the wood packaging pathway and high levels of non-compliance with ISPM#15 by Chinese shippers. What is APHIS going to do about this well-documented problem? APHIS certainly shouldn’t ignore these findings on the grounds that this particular wood-borer is less damaging than many others. Any chink in our phytosanitary programs that allows transport and entry of VLB can – does! – allow introduction of other woodborers.

The VLB also has been found in rustic furniture – often after the furniture has been sold to consumers. I discussed a 2016 example of this pathways in my February 2017 blog. Krishnankutty et al. (2020) suggest other possible pathways are wooden decorative items and nursery stock, particularly penjing (artificially dwarfed trees and shrubs).

Krishnankutty et al. (2020) note the importance of proper disposal of wood packaging once the cargo reaches its destination. Have any state phytosanitary officials enacted regulations targetting this source of invaders?

pallet “graveyard” – Photo by Anand Prasad, Davey Tree

The Risk to North America’s Forests Is Unknown

A climate-based model described in Krishnankutty et al. (2020) suggests that climate appears to be suitable for VLB across much of the continental United States, northern Mexico, and southern Canada. Only Florida, southern Texas, and high elevation and coastal regions of the western United States and Mexico states are unlikely to support the velvet longhorned beetle, based on climate. (The study did not consider whether host trees would be present.)

Asian and European sources list a broad host range consisting of at least 40 genera of conifers, hardwoods, and fruit trees (Krishnankutty et al. 2020). Still, as noted above, new studies seem to indicate a minimal impact on healthy trees in North America. Indeed, the principal Utah outbreak is in an orchard littered with pruned material.

With so many suitable hosts across so much of the country, the potential for damage is frightening.

Setting Priorities for Surveillance

The availability of data on both port interceptions and multiple detected outbreaks provides an opportunity to test procedures for carrying out early detection surveys. Improving the efficacy of early detection is critical since – as Wu et al. (2020) note – — the majority of infesting larvae would probably not be intercepted and would subsequently be transported to the cargo’s intended destinations. This is despite CBP’s best efforts to target inspection of wood packaging shipments based on shippers’ histories of non-compliance, targeting that I strongly support.

In response to this concern, Krishnankutty et al. (2020) analyzed pathways of introduction – 1) the types of imports associated with VLB-infested wood packaging, 2) ports where the beetle has been detected in recent years, plus 3) the presence and calculated probable volume of imports of types of commercial operations considered likely to transport the beetle. These included wholesale and retail sellers of products known to be risky and businesses involved with wood fuel processing, log hauling, logging, and milling of saw lumber (Krishnankutty et al. 2020).

They could test the value of this approach by comparing the calculated “intended destination counties” declared at import to actual detections of T. campestris. VLB was detected (by CAPS or other surveys) in either the same or a neighboring county for 40% of the intended destination counties.

This seems to be a high introduction rate; detections will probably rise now that a species-specific lure is available. What could this mean for the establishment rate? Is anyone going to repeat the comparisons to track such changes? Unfortunately, we lack sufficient data to compare the VLB establishment rate (whatever it turns out to be) to the rate for other wood-borers.

Focusing on their original intentions, Krishnankutty and colleagues considered the 40% correlation between intended destinations and VLB detections to be sufficiently rewarding to be one basis for setting priorities for surveys (Krishnankutty et al. 2020).

Krishnankutty et al. (2020) say that recognition of three established populations and widespread destinations of potentially infested wood packaging to climatically suitable areas points to the need to determine whether additional populations are already established – or might soon become so. I add this need is further supported by the frequent detections of low numbers of the VLB in at least seven other states (see above). They call for enhanced surveillance to determine where the VLB is.

Improved surveillance is now facilitated by Dr. Ann Ray’s identification of a specific pheromone that can be synthesized in a lab and used to lure VLB to traps. The pheromone is much more effective in attracting VLB than previous food-like lures used by CAPS as general-purpose attractants for wood-boring insects.APHIS had provided about $50,000 over four years from the Plant Pest and Disease Management and Disaster Prevention program (which receives funding through the Farm Bill) to Dr. Ray’s search for the species-specific pheromone.

what happens when detection fails –
dead champion green ash in Michigan

I will discuss detection efforts in a separate blog.

SOURCES

Haack, R. A. 2006. Exotic bark- and wood-boring Coleoptera in the United States: recent establishments and interceptions. Can. J. For. Res. 36: 269–288.

Krishnankutty, S.M., K. Bigsby, J. Hastings, Y. Takeuchi, Y. Wu, S.W. Lingafelter, H. Nadel, S.W. Myers, and A.M. Ray. 2020. Predicting Establishment Potential of an Invasive Wood-Boring Beetle, Trichoferus campestris (Coleoptera:) in the United States. Annals of the Entomological Society of America, XX(X), 2020, 1–12

Oregon Department of Agriculture, Plant Protection & Conservation Programs. 2019. Annual Report 2019.

Posted by Faith Campbell

SOD – questions that need answers

SOD in the nurseries

infected rhododendron
photo by Jennifer Parke
Oregon State University

As you may remember, in May 2019, we became aware of a troubling outbreak of the sudden oak death pathogen Phytophtora ramorum in the nursery trade. The discovery was made by Indiana authorities, who carefully inspected plants being sold in the state.

Briefly, 28 states initially learned that they might have received plants from the suspect sources. Later, APHIS determined that plants exposed to the pathogen had been sent to 18 states – Alabama, Arkansas, Iowa, Illinois, Indiana, Kansas, Kentucky, Michigan, Missouri, Nebraska, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Texas, Virginia, and West Virginia. Of these, seven (Iowa, Illinois. Indiana, Kansas, Missouri, Nebraska, Oklahoma) plus Washington were known to have received P. ramorum-positive nursery stock. [California Oak Mortality Task Force Newsletter August 2019]

The 2019 episode was just the latest of several occasions since 2004 in which infected plants have been widely distributed by the nursery trade, despite federal and state regulations.

APHIS delays in explaining the situation and what actions it was taking led the states to complain through a letter from the National Plant Board.

For discussions of the 2019 espisode, see my earlier blog or the California Oak Mortality Task Force newsletter for February 2020.

What have we learned from this episode?

1) Three West coast states – California, Oregon, and Washington – are a usual source for the nursery trade of plant taxa that happen to host the P. ramorum pathogen plants. These states’ climates are conducive to growth of these plants and of the pathogen. After repeated nursery outbreaks over 16 years, I think it is time to question continued reliance on such a high-risk source for these plants.

2) APHIS funds the federally-mandated inspection programs in the three states through the “specialty crops” line of the agency’s annual appropriations. Funding levels have apparently remained steady in recent years (COMTF Feb 2020), despite increases in the overall funding for the “specialty crops” line in recent years. I – and some of you! – have lobbied for these increases precisely in order to address the P. ramorum threat. Why has the funding not been increased?

3) While APHIS allocated $352,945 (COMTF February 2020) from the Plant Pest and Disease Management and Disaster Prevention program to help states carry out nursery surveys in 14 states following the 2019 incident, some of the affected states were not included in the program and some states that had not received suspect plants were. States that did not get funding in Fiscal Year 2020 (2020 award report) included three where P. ramorum-positive plants were detected: Iowa, Illinois, and Indiana; and one state that had a scare – Pennsylvania received plants but none tested positive. Seven states received P. ramorum survey funds through the Plant Pest and Disease Management and Disaster Prevention program although they had not received positive plants in the 2019 incident. These were Maryland, Massachusetts, Nevada, New York, North Dakota, Rhode Island, and South Carolina.

The Plant Pest and Disease Management and Disaster Prevention program distributes $70 million annually, and is not subject to annual appropriations. Does a national crisis play any role in determining which projects get funded? Or are decisions made entirely on a proposal by proposal basis and so depend on states’ priorities and individuals’ grant-writing skills?

4) Even now, on the verge of a new plant shipping season (if one occurs given the Covid-19 virus shutdowns), I have seen no public information clarifying how the inspection systems in Washington, British Columbia, and at the U.S. border failed to detect the infested plants before they were shipped. Trace-back efforts carried out by state and U.S. authorities pointed to a nursery in British Columbia as the original source of the infested plants. However, the Canadian Food Inspection Service (CFIA) determined that no Canadian nursery shipped infected plants to the U.S. in 2018 or 2019. See the next paragraph for a description of APHIS’ efforts to resolve this discrepancy.

According to information in the Oregon Department of Agriculture report for 2019, plant imports from Canada are inspected by DHS Customs and Border Protection (CBP) agriculture specialists, not by APHIS. Apparently, CBP has been relying on rules applicable to fruits and vegetables (Q-56) rather than the more stringent provisions of the plants for planting regulation (Q-37). Alerted by Oregon to the importation of 15 Euonymus plants infested by a federally-designated quarantine pest (a thrips), the National Plant Board sent a letter to APHIS in August 2019 asking that it correct CBP’s inspection process.

In March 2020, APHIS sent a letter to the states saying it had amended its Manual and guidance to CBP agricultural inspectors to clarify that all plants for planting must be handled in accordance with the more stringent Q-37 regulations. Furthermore, APHIS is working with CFIA to clarify understanding of each other’s P. ramorum procedures. The letter states that APHIS might consider prohibiting importation of P. ramorum hosts from Canada until CFIA demonstrates that it has adopted effective management measures.

This action by APHIS demonstrates a new seriousness in addressing P. ramorum. I hope this gravitas will persist and carry through to 1) strengthening theregulatory conditions governing domestic production and sales see following section); 2) providing financial and other support to the states (see above about the “specialty crops” appropriation); 3) funding additional studies to clarify the host list and modes of transmission; and 4) using its authority under NAPPRA to curtail imports of plants from Vietnam and other areas where there are large numbers of newly detected Phytophthora species that might threaten North American plant species.

infested plants detected by Indiana inspectors

I question sufficiency of inspection and mitigation regime

(as described in the February 2020 COMTF newsletter)

When alerted to the infected plants turning up in Indiana, in May 2019, Washington State Department of Agriculture (WSDA) began trace-back investigations. The large wholesale shipping nursery that supplied the plants appears to have acted quite responsibly – it destroy 54,000 plants, cooperated in the Critical Control Point assessment, and implemented mitigation actions. However, I am disturbed to read that the destruction of plants in the 10-meter quarantine radius from plants detected to be infected was a voluntary action. Why don’t the regulations require destruction of nearby hosts?

Descriptions of the western states’ inspection systems – those tied to this specific nursery episode and routine inspections under federal and state P. ramorum programs – indicate to me that P. ramorum is circulating in nurseries in the west coast states, but is evading detection. I cite examples from all three states.

One of the positive nurseries in California in 2019 had been found to be positive in previous years and is considered to be in compliance with quarantine regulations. Yet these measures have not been sufficient to ensure that the nursery is pathogen-free now – as illustrated by its testing positive in 2019.

In Oregon, a retail nursery found to have infected plants destroyed all host material located in the block. Is this action sufficient to ensure that the nursery is now pathogen free? What about the soil, water, cull piles, etc.? Oregon trace-back surveys led to various suppliers that had previously not been known to be infested. This leads me to think that the pathogen is circulating below regulators’ attention.

In the wake of the 2019 crisis, Washington State Department of Agriculture (WSSA) inspected “opt-out” nurseries – those that had decided not to join APHIS’ program to ship interstate, but continued to ship within the state. WSDA relied on visual inspection only of host material; the agency collected no samples from plants or nursery soils, water, or plant waste (Feb 2020 COMTF). Given all we know about the difficulty of detecting P. ramorum, I think we need more intense inspections that do sample soils, water, and any nearby plant waste (cull piles).

Meaning of Stream Detections?

The P. ramorum pathogen continues to turn up regularly in water bodies. At a botanical garden in Washington State, plant samples have been negative since February 2016. However, water baits from a small pond were positive in 2019 and previous years. Washington’s Sammamish Riverhas been positive since 2007. In the Southeast, seven streams tested positive in 2019. Most if not all have been positive consistently or at least repeatedly for years. All these positive streams are associated with nurseries previously positive for the pathogen. However, plants in the vicinities of these streams show no symptoms.

The same is true in Vietnam: P. ramorum was found in seven out of eight high-elevation streams sampled, but none of the plants belonging to families that have proved highly vulnerable in North America and Europe had any disease symptoms (Jung et al, 2020. A Survey in Natural Forest Ecosystems of Vietnam Reveals High Diversity of both New and Described Phytophthora Taxa including P. ramorum. Forests, 2020, 11). The Jung et al. 2020 findings are discussed in the COMTF Feb. 2020 newsletter and my recent blog.

SOD in the woods

dead coast live oak in California
Joseph O’Brien, USFS

The COMTF February 2020 newsletter summarizes the worrying increase in disease in California woodlands in recent years, which followed the record wet spring of 2017. Aerial surveys documented a big increase in dead tanoak trees and affected acreages in 2018, followed by a smaller increase in 2019 – although still much higher than in 2017. [Details: in 2017, 21,000 dead trees were mapped across 18,000 acres; in 2018, 1.6 million dead trees across 106,000 acres; in 2019, 885,000 dead trees across 92,000 acres.]

California officially records as infested only those counties where infestations have been confirmed by California Department of Food and Agriculture or county Agricultural Commissioners. California currently lists 15 counties as infested. Recent observations by academics or other non-officials of Phytophthora ramorum in Del Norte and San Luis Obispo counties have not yet been confirmed by officials so neither is included in the official quarantine. I understand the need to be certain about reported detections, but we should remember that the disease is probably more widespread than official data indicate.

The newsletter reports Oregon’s treatment efforts – which have totaled 7,300 acres since 2001. I am pleased that Oregon Department of Forestry now has an Environmental Quality Incentives Program (EQIP) project with the USDA Natural Resources Conservation Service and that both the Bureau of Land Management and USDA Forest Service are treating infected areas.

treatment of SOD-infested site
in Oregon
USFS

Still, the quarantine area now covers 31% of Curry County, the EU1 lineage is established in the forest, and ODF and its partners lack sufficient resources to treat all infected areas.

Washington State doesn’t have (known) forest infestations, but it continues to find the pathogen in water bodies; the Sammamish River in King County has been positive since 2007.

In the East, seven states (Alabama, Florida, Georgia, Mississippi, North Carolina, South Carolina, and Texas) participated in the USFS Cooperative Sudden Oak Death Early Detection Stream Survey in 2019. A total of 48 streams were surveyed. P. ramorum was detected from seven streams – five in Alabama, one in Mississippi, and one in North Carolina. All positive streams were associated with nurseries previously positive for the pathogen.

Finally, the newsletter summarizes an article providing advice on managing SOD’s impacts – specifically, conservation of tanoak.

SOURCES

February 2020 issue of the California Oak Mortality Task Force newsletter http://www.suddenoakdeath.org/wp-content/uploads/2020/02/COMTF-Report-February.pdf

Oregon Department of Agriculture Plant Protection and Conservation 2019 annual report

Posted by Faith Campbell

Hope for eastern hemlocks – IF funding can be obtained

eastern hemlocks in Great Smoky Mountains National Park

As we all know, eastern (Tsuga canadensis) and Carolina (T. caroliniana) hemlocks have suffered huge losses due primarily to the introduced hemlock woolly adelgid (Adelges tsugae – HWA). In New England, there has been more than a 60% decrease in total hemlock basal area since 1997 and a virtual absence of hemlock regeneration in HWA-infested areas. HWA continues to spread – most recently into western Michigan and Nova Scotia (all information, unless otherwise indicated, is from Kinahan et al. 2020; full citation at end of this blog). [However, Morin and Liebhold (2015) found that hemlock basal volume continued to increase for the first 20 years or so after invasion by the adelgid, due to ingrowth of immature hemlocks. See “results” in Morin et al., full citation at the end of the blog.]

This loss deprives us of a gorgeous tree … and unique habitats. Hemlock-dominated forests were characterized by deep shade, acidic and slowly decomposing soil, and a cool microclimate. They provided unique and critical habitat for many terrestrial and aquatic species.

A team of scientists based at the University of Rhode Island has carried out an experiment comparing cuttings from eastern hemlocks apparently resistant to HWA to susceptible ones. Matching sets of resistant and susceptible trees were planted at eight sites in seven states – Ithaca and Bronx, NY; Boston; southern CT; Lycoming County, PA; Thurmont, MD; southern WV; and Waynesville, NC. All plantings were within or adjacent to forests containing HWA-infested hemlocks.

After four years, 96% of the HWA-resistant hemlocks had survived, compared to 48% of the control plants. The HWA-resistant plants were 32% taller, put out 18% more lateral growth, had 20% longer drip lines, and were in 58% better condition. HWA was found on trees at only three out of the eight plots. HWA density on resistant eastern hemlocks was 35% lower than on HWA-susceptible hemlocks, although this difference was not statistically significant.

Trees in all eight plots were infested with elongate hemlock scale (Fiorinia externa – EHS), a second insect damaging hemlocks in eastern North America. However, the HWA-resistant hemlocks had EHS densities 60% lower than those of the controls.

Kinahan et al. note that identification and use of host tree populations’ potential for pest resistance has played a role in other programs managing non-native pests and pathogens, including Dutch elm disease and chestnut blight.

The same scientists note that significant effort has been put into biocontrol or insecticides for management of hemlock woolly adelgid, but without achieving the desired improvement of forest health. Attempts to cross eastern hemlocks with HWA-resistant hemlocks unfortunately produced no viable offspring. However, Kinahan et al. were inspired to explore possible genetic resistance within natural populations of eastern hemlocks by the 1) evidence of resistance in Asian and western hemlocks; 2) the different foliar terpene profiles in those species; and 3) the presence of apparently healthy mature hemlock trees growing in proximity to heavily infested trees.

They asked forest managers and other concerned groups to help locate stands with trees that were mature and apparently completely healthy, were located within HWA-devastated hemlock stands, and had not been chemically treated. They chose a small stand of eastern hemlocks growing within the Walpack Fish and Wildlife Management Area in northern New Jersey. This stand was called the “Bulletproof Stand”. They evaluated HWA resistance in five of these trees, then chose two for propagation and planting in the test.

New Jersey’s “bullet-proof stand” on the left
photo by Richard Casagrande

The trees were planted in September 2015. Due to funding gaps, they were not revisited for four years. Thus, Kinahan et al. re-evaluated the resistant and vulnerable trees in Autumn 2019 – with the results I reported above.

Does this study prove that clonal propagation of apparently resistant hemlocks is an effective strategy to restore the species?

It is not that simple.

The difference in survival and condition was striking, but the authors note several caveats:

1) they had not recorded pre-experiment data on plant height or other variables, so they cannot be certain that variation in initial plant height or dripline did not contribute to current treatment-level differences in these variables.

2) they cannot distinguish between the impacts of HWA and EHS on plant growth.

3) since they could not monitor the planting sites for four years, they cannot definitively link increased mortality of HWA-susceptible trees to higher pest densities. However, the lower pest densities and higher survival of HWA-resistant hemlocks are consistent with herbivore-driven tree mortality.

They also cannot assess the impact of other environmental stressors (drought, cold, etc.) on their results.

4) The small number of trees planted at each site prevented detailed site-level analyses.

The scientists conclude that their work is most appropriately viewed as a ‘proof of concept’ experiment highlighting the need for future research exploring how HWA-resistant eastern hemlocks might best be integrated into existing HWA management.

Unfortunately, the Rhode Island researchers report they cannot persuade the US Forest Service to support continuing this effort. Will these promising hints not result in action?

Kinahan et al. stress the importance of the reduced pest densities (both HWA and EHS) on the putatively resistant hemlocks. They think this might be a result of the higher terpene concentrations in the twigs and needles. Finally, they note that lower densities of sap-feeding herbivores may also indirectly provide protection against other consumers, including gypsy moth (Lymantria dispar) and hemlock looper (Lambdina fiscellaria).

SOURCE

Kinahan, I.G., G. Grandstaff, A. Russell, C.M. Rigsby, R.A. Casagrande, and E. L. Preisser. 2020. A four-year, seven-state reforestation trial with eastern hemlocks (Tsuga canadensis) resistant to hemlock woolly adelgid (Adelges tsugae). Forests 11: 312

Morin, R.S. and A.M. Liebhold. 2015. Invasions by two non-native insects alter regional forest species composition and successional trajectories. Forest Ecology and Management 341 (2015).

Posted by Faith Campbell

P.S. I have been working with colleagues to promote a more coordinated and well-funded program to combat non-native forest pests – including much greater reliance on identifying and breeding resistance to the pest. Visit here to see this effort.