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Hopeful Developments for One Bioinvader – KSHB; Possible implications of research & management recommendations

Willow forest in the Tijuana River Valley killed by Kuroshio shot hole borer
the “boom” part of the cycle
photo by John Boland

I have blogged earlier about the damage caused by the Kuroshio shot hole borer (KSHB, Euwallacea kuroshio), which is one of two invasive shot hole borers established in southern California. The beetle and its symbiotic fungi had caused amazing levels of damage in the Tijuana River Valley in San Diego County, California. The wood borer is described here and here.

Most of the earlier blogs focused on the absence of a response by California’s phytosanitary agency and here – until John Kabashima created sufficient political demand for a response.

A scientist who has devoted considerable effort to understanding the KSHB is John Boland of Boland Ecological Services. He has posted annual reports analyzing five years of the outbreak in the Tijuana River Valley (see full citations at the end of the blog). His principal findings (Boland and Uyeda 2020): the invasion went through a boom and bust cycle, with willows in the wettest parts of the estuary having largely recovered. So far, Kuroshio shot hole borers have not re-infested the growing trees, despite the presence of all conditions seeming to favor invasion. His principal worry is enhanced invasion by the non-native grass or reed Arundo donax.

The study site is a coastal floodplain crossed by an intermittent stream. The Tijuana River valley provides several ecosystem services, including filtering pollutants before the water reaches the ocean, open space, and important wildlife habitat, including Critical Habitat for the federally endangered least Bell’s vireo (Vireo bellii pusillus).

There is a mosaic of forests of different ages and at different distances from the current flows. They range from wet forests growing in the current river beds; dry forests growing in older river beds that get some current flows; and scrub forests growing far from current river flows. All these forests are dominated by two willows: the black willow (Salix gooddingii) and the arroyo willow (Salix lasiolepis). Both are preferred hosts of KSHB; both are pioneer species that establish in disturbed wet areas; both resprout vigorously. The riparian scrub woodlands surrounding the forests are dominated by the perennial shrub, mule fat (Baccharis salicifolia), with scattered willows of both species (Boland and Uyeda 2020).

The river carries high levels of raw sewage and industrial waste from Tijuana, Mexico. Raw sewage contains important plant nutrients – nitrogen, phosphorus and potassium. The willows in or near the nutrient-enriched channel water were growing quickly and vigorously, and had wood characteristics that differed significantly from those of trees in the dry or scrub forests. Dr. Boland notes that these trees’ phloem sap is loaded with sugars from the fast-growing leaves, and xylem sap is loaded with nutrients from the enriched soil. His Enriched Tree Hypothesis (discussed further below) suggests that these nutrients promote fast growth of the symbiotic fungi and ideal conditions for KSHB (Boland and Woodward 2019).

Boland and his colleagues have carried out detailed annual field surveys of the infestation since 2015. Using the same study plots in each year, they analyzed infestation and mortality rates, canopy damage, and survivorship of tagged willows.

Funding originally came from the U.S. Navy and U.S. Fish and Wildlife Service – agencies probably worried about the potential destruction of the vireos’ habitat. As of 2019 KSHB had infested 91% of all the willows in the valley – estimated to be more than 350,000 willows. KSHB had killed 30% of the trees, or nearly 123,000 (Boland 2019). Dr. Boland considers this estimate to be an underestimate because he could not accurately carry out surveys of individual trees in the extensively-damaged Wet Forest units in 2018. There was considerable variation in pest impacts depending on host trees’ proximity to the intermittent river. Of all of the willow deaths in the valley, 93.8% occurred in the Wet Forests, 6.1% in the Dry Forests and 0.1% in the Scrub Forests. This variation occurred even though the sites contain the same willow species (Boland and Uyeda 2020).

Infestation rates over the four-year period averaged 99% of willows in the Wet Forest units, 82% in the Dry Forests and 3% in the Scrub Woodlands. Considering 2019 alone, the overall infestation rate was only 9%. Looking at differences among forest types, 1% of the willows in Wet Forests were infested (down from 95% in 2015), 29% of the willows in dry forests (down from 73% in 2016), and 0% of the willows in the scrub forests (down from 2% in 2018). (2019 infestation rates from Boland and Uyeda 2020; earlier years from Boland 2019.)

Infestation rates had to be very high before trees died, but then mortality was very high. Only after sites reached infestation rates of more than 95% did sites have significant mortality rates – and then, very high — up to 97%. In agreement with other findings, most of the high-mortality sites were in Wet Forest units. These had a mean maximum mortality rate of 49%. The mean maximum mortality rate was only 9% in Dry Forest and 2% in Scrub Forest units (Boland and Uyeda 2020).

The size of the tree is also important. In the Wet Forests, in 2019, infestation rates were 0% for seedlings and young trees; 3% for the relatively undamaged trees that are more than 5 years old; and 1% of the resprouting adult trees that had been broken during the first wave of invasion. KSHB prefers young trees with a trunk dbh of at least 4.5 cm. Smaller trees were generally avoided. Trees with very large dbh (> 30 cm) appear to be able to survive a KSHB attack (Boland and Uyeda 2020).

At the end of the five year period, Dr. Boland had documented interesting/puzzling findings.

Recovery of the willow forest in Tijuana River Valley – 2019
photo by John Boland

Wet Forests

KSHB in the valley went through a rapid boom-and-bust cycle. In the Wet Forests, KSHB infestation progressed over the course of a few months from barely noticeable to heavy infestation and dramatic canopy collapse. Infestation rates of 80 – 95% in the West Forests in 2015 and 2016 led to virtual elimination of the canopy between 2016 and 2017 as tunnel-ridden trees were broken by wind storms. These severe damage levels occurred over 94 acres (Boland and Uyeda 2020).

After apparently depleting their preferred hosts in the wettest parts of the forest, beetle numbers fell and host trees began a rapid recovery. Mean canopy cover rose from 5% in 2017 to 56% in 2019. This recovery has taken three forms: survival of a few, scattered mature infested trees (‘Big Trees’) which grew new wood over KSHB galleries (Boland 2019); resprouting of mature KSHB-damaged trees (‘resprouts’); and seeding of new trees (‘seedlings’). Some of the forests have recovered so much in just 4 years that they are now similar to their pre-KSHB stature (Boland and Uyeda 2020).

Dr. Boland suggests that KSHB is promoted by high nutrient (pollution) levels in the water, which result in rapid growth by trees near the most steady of the intermittent streams. He has developed an Enriched Tree Hypothesis (explained briefly below; for a full discussion, see Boland and Woodland 2019).

As of autumn 2019, beetles have not attacked the recovering hosts – despite apparently favorable conditions and the absence of management interventions. 2019 infestation rates were 3% of the remaining Big Trees, 2% of the resprouting trees, 1% of the young trees, and 0% of the seedlings. Dr. Boland suggests three possible reasons (Boland and Uyeda 2020), which I will discuss below.

The resprouting trees are now old & vigorous enough to flower

It is likely that these recovering willow forests will provide good breeding habitat for least Bell’s vireo (all Boland publications).

Dry Forests

Infestation in the Dry Forests spread more slowly – infestation rates averaged 82% in the Dry Forests over four years. The infestation progressed more slowly and the canopy remained mostly intact. But in 2019 the infestation rate in the Dry Forest was substantially higher than in the Wet Forest — 29% versus 1% (Boland and Uyeda 2020).

Still, only 16% of more than 200 willows tagged in February 2016 had been killed by KSHB by autumn 2019. Among the living trees were three quarters of trees already infested in 2016, and half of trees that became infested after 2016 (Boland and Uyeda 2020).

Lack of Reinfestation (Boland and Uyeda 2020).

The absence of reinfestation is surprising, especially because the conditions thought favorable to KSHB are all present:

1. The regenerating trees belong to host species known to be preferred – black and arroyo willows.

2. The regenerating trees have reached the preferred size with trunk dbh exceeding 4.5 cm. In fall 2019 the trees in the recovering Wet Forests included many resprouting trees with mean diameters of 6.5 cm, and many new seedlings with mean diameters of 11.7 cm.

3. Recovering forests are located in the preferred nutrient-rich sites. Sewage levels remain high.

4. The trees in the recovering forests are in the condition preferred by KSHB, i.e., the trees are fast-growing and vigorous.

5. The KSHB is present – in low numbers in the Wet Forests, more numerous in Dry Forests which are < 1 km away.

It is not known whether KSHB will eventually re-infest.

The KSHB infestation reversed the presence of large trees. Originally 53% of the large trees were in the Wet Forests, 38% in the Dry Forests. The KSHB invasion damaged so many of the trees in the Wet Forests that now they represent only 24% of all the ‘Big Trees’ in the Valley; 58% of the ‘Big Trees’ are now in the Dry Forests. In many Dry Forests the remaining tall trees form a continuous canopy layer, whereas in the polluted Wet Forests they are usually only single ‘Big Trees’ (Boland and Uyeda 2020).

Other plant species

Dr. Boland expresses great concern about the spread of the invasive plant, Arundo donax, in response to canopy openings caused by the initial invasion and canopy collapse (willow trees are Arundo’s only competitors in the valley).

Surveys during fall 2019 found that most plant species growing in the Tijuana River Valley are native, dominated by the willows (mean cover of 60%). The most abundant non-native species is castor bean (10% cover). Arundo had a mean cover of only 6% in the belt transects, but it was more abundant outside the transects. Arundo is spreading as rhizomes cut loose by bulldozing, disking, and mowing on property managed by International Boundary and Water Commission (Boland and Uyeda 2020). Both willows and Arundo had increased their percent cover between 2018 and 2019 (Boland 2019).

Dr. Boland’s Recommendations (Boland and Uyeda 2020)

1) The different invasion trajectories in the three habitat types contradict some researchers’ expectation that all trajectories are similar from regardless of site characteristics or that a light infestation must be recent while a heavy infestation must be old.

2) Unique characteristics of the Tijuana River valley – especially the high sewage levels – mean that the severe infestation and damage seen there should not be expected to occur at other natural, unpolluted riparian sites.

3) Dr. Boland disputes recommendations that “heavily infested” trees be removed because they are doomed and support beetle reproduction. Although Dr. Boland studied primarily willows, he did evaluate 24 California sycamores (Platanus spp.) that had been planted in various parts of the valley.

He found that none had died and only two (8%) were infested. The two infested trees were lightly infested and growing near the sewage-enriched stream. Dr. Boland concluded that sycamores were also unlikely to be heavily infested and killed in habitats less favorable to shot hole borers (Boland 2019).

4) The ease with which native willows became densely established in wet forest sites after the first infestation wave leads Dr. Boland to advocate reliance on natural restoration projects … as long as Arundo invasion can be controlled.

5) Avoid over-fertilization or over-watering of trees in planted landscapes.

6) Focus detection searches for KSHB in nutrient-enriched areas. … e.g., near storm drain outfalls.

Research recommendations:

A) Determine why KSHB has not substantially reinvaded the recovering willow forests despite the presence of preferred species in “correct” condition and size. Dr. Boland suggests testing of three hypotheses:

Induced response of hosts. Have the infested willows changed their chemistry as a result of the borer attack, thus increasing their resistance ….
Overall forest structure. Have the less dense and more mixed forest stands reduced attractiveness to the beetle?
A disease or predator. Has a biocontrol agent been introduced accidentally? None has yet been identified …

B) Understand the possible mechanisms for the high initial infestations rates in the Wet Forests.

To evaluate the Enriched Tree Hypothesis measure the sugars and nutrients (both concentrations and loading rates) in trees subject to differing amounts of sewage or fertilizers. Then conduct controlled trials in the lab on the growth response of ISHB’s fungal symbionts to various sugar and nutrient concentrations and loading rates.
Evaluate whether willows growing in the nutrient-enriched sites produced fewer tannins that might inhibit beetle and fungal growth.

C) Can ISHB disperse by wind? Dr. Boland recommends searching for ISHB in the air high above infested trees; this could involve the use of nets or traps attached to aircraft, hot-air balloons, helium balloons or drones.

D) Determine whether surviving mature trees have superior characteristics re: morphology, vigor, and pest or disease resistance that make them less vulnerable to KSHB attack.

E) Incorporate site and ecology data and varying levels of host vulnerability into models predicting KSHB impacts. Include the ecological costs of removing the trees.

My questions

Are other scientists applying these findings in their research on KSHB or polyphagous shot hole borer outbreaks in other parts of California? I am particularly interested in the issues of possible resistance in some willows – innate or induced; and the potential role of excess nutrients in promoting fungal and beetle growth. Are they finding the ecological components of the Enriched Tree Hypothesis to be helpful in defining the impact of PSHB outbreaks in other parts of the state, and of older ages?

SOURCES

Boland, J.M. 2109. The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley. Final Report for Naval Base Coronado under Cooperative Agreement N62473-18-2-0008

Boland, J.M. and D.L. Woodward. 2019. Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern Calif: the Enriched Tree Hypothesis. PeerJ 7:6812

Boland, J.M. and K.A Uyeda. 2020. The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley 2019-20 (Year 5) Final Report. For Naval Base Coronado, Department of Navy and Southwest Wetlands Interpretive Association. Under Cooperative Agreement N62473-18-2-0008

All these reports are available here: The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley — Tijuana Estuary : TRNERR

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

Outrageous – Asian longhorned beetle Appears Again – Will US Respond Appropriately?

Here we go again … another Asian longhorned beetle population established in the U.S.

For the ninth time in 24 years, the Asian longhorned beetle (ALB) has been found in North America – this time in South Carolina.

This means thousands – perhaps tens of thousands – of trees will be removed. Thousands more will be injected with imadacloprid. Millions of dollars will be spent. There will be uncounted aesthetic and spiritual losses. There will be unmeasured damage to at least the local environment – which probably includes bottomland hardwood forests – protection of which South Carolina has declared to be a conservation priority. All this destruction is necessitated by the need to prevent catastrophic damage to North America’s hardwood forests by the ALB.

By early August I have learned that the South Carolina outbreak has been present for seven years or longer, and that it might be related to the Ohio outbreak (which was detected in 2011 but was probably introduced at least four years earlier). APHIS reports that, as of the end of July, nearly 1,300 infested trees had been detected. The area around the neighborhood where the detection was made is swampy – complicating search and removal operations and probably home to many box elder and willows – preferred hosts for the ALB.

Why did we let this happen? Why do we persist with a policy that has allowed repeated introductions of this pest via the well-documented wood packaging pathway? After all, we learned about this risk 22 years ago – after the ALB introductions to New York and Chicago. We have had plenty of evidence that the policy is failing. We know how to stop this. Why do we – through our elected and appointed government officials – not act to prevent it?

What We Need: a New, Protective Policy

With live pests continuing to be present in wood packaging 14 years after the U.S. and Canada imposed the treatment requirements in ISPM#15 – and 21 years after we required China to treat its wood packaging – we urgently need better federal policy. I have long advocated:

USDA APHIS join Bureau of Customs and Border Protection in penalizing violators for each violation; stop allowing five violations over a 12-month period before applying a penalty.
APHIS and the Canadian Food Inspection Agency (CFIA) should apply their rights under Section 5.7 of the World Trade Organization Sanitary and Phytosanitary Agreement to immediately prohibit China from packaging its exports in wood. China can use crates and pallets made from such alternative materials as plastic, metal, or oriented strand board.
APHIS and CFIA should being the process of supporting permanent application of this policy to China and other trade partners with poor compliance records. This step would require that they cite the need for setting a higher “level of protection” and then prepare a risk assessment to justify adopting more restrictive regulations.
USDA Foreign Agriculture Service (FAS) should assist U.S. importers to determine which suppliers reliably provide wood packaging that complies with ISPM#15 requirements.
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, especially
- Update the Haack study of pest approach rate.
- Determine whether high rates of pest infestation of wood bearing the ISPM#15 mark results from fraud or failures of treatment – and whether any failures are due to mistakes/misapplication or shortcomings in the treatment themselves.
- Allocate the risk among the three major types of wood packaging: pallets, crates, and dunnage.

These folks work for us – tell them to protect our forests!

See also the recommendations of the Tree-Smart Trade program at www.tree-smart-trade.org

Tree-Smart also has a Twitter account: @treeSMARTtrade

Justification

The ALB poses a threat to 10% of US forests and nearly all of Canada’s hardwoods, so eradication of the South Carolina outbreak is essential. For a longer discussion of ALB introduction history, the threat, and eradication efforts to date, visit here. https://www.dontmovefirewood.org/pest_pathogen/asian-long-horned-beetle-html/).

Another ALB Outbreak in the US: No Surprise

This Chinese insect is a world traveler. It has been detected 36 times outside its natural range: in North America, Europe, and Japan. Seventeen of these outbreaks have been detected since 2012 (Eyre & Haack 2017). These 17 introduction have occurred six years or later after the 2006 implementation of the International Standard for Phytosanitary Measures (ISPM) #15 – which was intended to reduce the likelihood of such introductions. .Ten of the outbreaks have been eradicated (Eyre & Haack 2017; APHIS press release October 2019). This includes four in the United States and Canada; see here.

Despite U.S. and international efforts, ALB and related pests have been detected continuously in imported goods. U.S. and European data (Eyre and Haack 2017) document rising numbers of Cerambycids detected in wood packaging in recent years. (For a description of pest prevention efforts, see Fading Forests II and III here and this blog).

It is also not surprising that the newly introduced pest is from China. It has long been among countries with the worst records on implementing ISPM#15.

The APHIS-CBP joint study of pest interceptions over the period 2012 – 2017 (Krishnankutty et al. 2020b) found the highest numbers of interceptions came from Mexico, China, and Turkey. During the period 2011 – 2016, China accounted for 11% of interceptions (APHIS interception database – pers. comm. January 2017).

These numbers reflect in part the huge volumes of goods imported from China. But China’s poor performance has continued, perhaps even increased in recent years. For example, consider the choice of wood used to manufacture packaging. Authorities recognized by the late 1990s that wood from plantations of Populus from northern China was highly likely to be infested by the Asian longhorned beetle. Yet, more than a dozen years later, this high-risk wood was still being used: between 2012 and 2017, the ALB was intercepted six times in wood packaging made of Populus wood – each time originating from a single wood-treatment facility in China (Krishnankutty et al. 2020b).

The location just outside Charleston also is not a surprise. Charleston ranked seventh in receipt of incoming shipping containers in 2018. Charleston received 1,022,000 containers, or TEUs measured as 20-foot equivalents, in 2018 (DOT report). This was a 14% increase over the 894,000 TEUs in 2017 http://www.marad.dot.gov/MARAD_statistics/index.html – click on “trade statistics”, then “US Waterborne trade” (1st bullet). I expect decreased import volumes in 2019 and 2020 due to the tariffs/trade war and the 2020 economic crash linked to the Covid-19 virus.

Why US and International Policy Still Fails

Leung et al. (2014) estimated that implementation of the International Standard of Phytosanitary Measures (ISPM)#15 resulted in only a 52% reduction in pest interceptions. They concluded that continued implementation at the 2009 level of efficacy could triple the number of wood borers established (not just intercepted) in the U.S. by 2050.

Since 2010 the Department of Homeland Security’s Bureau of Customs and Border Protection (CBP) has found an average of 794 shipments infested by pests each year (Harriger). In 2019 specifically, live pests were found in 747 shipments (Stephen Brady, CBP, April 2020). These violations were occurring four to 13 years after the U.S. began implementing ISPM#15 in 2006. According to my calculations, based on estimates of pest approach rates by Haack et al. (2014), these detections probably represented about eight percent of the total number of infested shipments entering the country each year.

And there are good reasons to think this estimate is low. First, Haack et al. (2014) did not include imports from China, Canada, or Mexico in their calculations. Both China and Mexico rank high among countries with poor compliance records. Second, Haack and Meissner based their calculations on 2009 data – 11 years out of date. Since 2009, 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 wood. Also, countries and trading companies have 11 more years of implementation – so they might have improved their performance. I have asked several times that APHIS commission a new analysis of Agriculture Quarantine Inspection Monitoring data. We all need an up-to-date determination of the pest approach rate, not only before but also after the CBP action. Without it, there’s no evidence whether the more aggressive enforcement stance CBP adopted in 2017 (see below) has led to reductions in non-compliant shipments at the border.

Another demonstration of the failure of ISPM#15 is the repeated presence of the velvet longhorned beetle (Trichoferus (=Hesperophanes) campestris) in wood packaging and its establishment in at least three states (Krishnankutty, et al. 2020a; also see the discussion in my recent blog here).

Astoundingly, data indicate that 97% of wood packaging infested with pests bears the stamp certifying that the wood has been treated according to the requirements of ISPM#15 – and hence should be pest-free (Eyre et al. 2018; CBP interception data). In other words, the presence of the stamp is not a reliable indicator of whether the wood has indeed been treated nor that it is pest-free. Scientists have speculated for years why this is the case. ALB’s new arrival provides an impetus to finally answer this question and to ensure policy reflects the answer.

What Federal Agencies Are Doing to Better Prevent Introductions

In contrast to such a comprehensive approach, this is what changes are under way.

CBP strengthened its enforcement in November 2017. The agency’s total “enforcement actions” increased by 400% from 2017 to 2018 (Sagle, pers. comm). The 2019 data show decreases, in absolute numbers, from earlier years in all categories: a 19% decrease below 2010-2018 in average number of shipments intercepted; a 13% decrease in number of shipments intercepted because the wood packaging lacked the ISPM#15 mark; and a decrease of 6% in the number of shipments intercepted that had a quarantine pest (Stephen Brady, CBP, April 2020). However, one year of interception data do not provide a basis for saying whether CBP’s stronger enforcement has resulted in a lower number of shipments in violation of ISPM#15 approaching our shores. Again, I call for APHIS to repeat Haack et al. (2014) study.

Harriger reported that CBP is also trying harder to educate importers, trade brokers, affiliated associations, CBP employees, and international partners about ISPM#15 requirements. CBP wants to encourage them to take actions to reduce all types of non-compliance: lack of documentation, pest presence in both wood packaging and shipping containers, etc.

APHIS has not altered its long-standing policy of allowing an importer to rack up five violations over a 12-month period before imposing a penalty. Instead, APHIS has focused on “educating” trade partners to encourage better compliance. For example, APHIS worked with Canada and Mexico – through the North American Plant Protection Organization — to sponsor workshops for agricultural agencies and exporters in Asia and the Americas

APHIS also planned to host international symposia on wood packaging issues as part of events recognizing 2020 as the International Year of Plant Health. These symposia have been postponed by travel and other restrictions arising from the coronavirus pandemic.

The Broader Significance of Continuing Wood Packaging Problems

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 rely on exporting countries to take the actions necessary to meet the importing countries’ plant health goals. The ISPM#15 experience undermines the very premise of these international agreements.

If we cannot clean up the wood packaging pathway – which involves boards or 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 phytosanitary measures, 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.

SOURCES

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 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 US. PLoS ONE 9(5): e96611.

Kevin Harriger, US CBP. Presentations to the annual meetings of the Continental Dialogue on Non-Native Forest Insects and Diseases over appropriate years. See, e.g., https://continentalforestdialogue.org/continental-dialogue-meeting-november-2018/

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

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

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

U.S. Department of Transportation, Maritime Administration, U.S. Waterborne Foreign Container Trade by U.S. Customs Ports (2000 – 2017) Imports in Twenty-Foot Equivalent Units (TEUs) – Loaded Containers Only at https://ops.fhwa.dot.gov/freight/freight_analysis/nat_freight_stats/docs/06factsfigures/fig2_9.htm and

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

Posted by Faith Campbell

Unique Black Ash Wetlands – Threatened by Emerald Ash Borer

Another unique ecosystem being severely damaged by non-native tree-killing pests are the wetlands dominated by black ash (Fraxinus nigra). Black ash typically grows in fens, along streams, or in poorly drained areas that often are seasonally flooded. Such swamps stretch from Minnesota to Newfoundland; in the three states of Michigan, Wisconsin, and Minnesota, they cover a total of over 2 million hectares (Kolka et al. 2018).

Recent research allows us to understand the impending loss to these unique ecosystems that will be caused by the emerald ash borer (EAB).

Hydrology is the dominant factor that influences a host of ecosystem functions in black ash wetlands. Water levels are largely determined by a combination of precipitation and evapotranspiration rates. Black ash can thrive in wetter areas than most other tree species (Slesak et al. 2014). Water tables in these swamps are typically above the surface throughout early spring, followed by drawdown below the surface during the growing season with periodic rises following rain events. Water table drawdown coincides with peak evapotranspiration following black ash leaf out, demonstrating the fundamental control that this species has on animal and other plant communities (Kolka et al. 2018; Slesak et al. 2014).

Ecological Importance

Black ash generally dominate the canopy of these wetlands. Ash density can range from about 40% to almost 100%. Several other tree species are present, including northern white cedar (Thuja occidentalis), red maple (Acer rubrum), American elm (Ulmus americana) (Kolka et al. 2018), quaking aspen (Populus tremuloides), American basswood (Tilia americana), and bur oak (Quercus macrocarpa) (Slesak et al. 2014), balsam fir (Abies balsamea), balsam poplar (Populus balsamifera), and speckled alder (Alnus incana) (Youngquist et al. 2020). Black ash, by maintaining low water levels during the growing season, creates conditions under which these other trees can live but not thrive (summary of study by B.J. Palik, USDA Forest Service, here. Most other species lack the physiological adaptations of black ash or face pathogenic constraints (e.g., Dutch elm disease on American elm Ulmus americana) (Kolka et al. 2018).

Ash trees in these swamps are uneven-aged with canopy tree ages ranging from 130–232 years (Slesak et al. 2014). This complexity provides important habitat for many wildlife species, including ground beetle community assemblages (Kolka et al. 2018) and an abundance of aquatic macroinvertebrates. These are characterized and dominated by mollusks (Sphaeriidae, Lymnaeidae, Physidae), annelids (Lumbriculidae, Hirudinea), caddisflies (Limnephilidae, Leptoceridae), and dipterans (Chironomidae, Culicidae) (Youngquist et al. 2020).

A major concern is that loss of trees – especially ash – might result in open marshes dominated by grasses, especially lake sedge (Carex lacustris). Conversion to sedge-dominated marshes has been observed in areas where trees have been removed as part of experiments to test various ecosystem responses to loss of the ash component (Slesak et al. 2014). Even if other trees took the place of ash, the substitutes might not support the same animal communities (see below).

Impact of Emerald ash borer and loss of black ash

Black ash is highly susceptibility to the EAB (Engelken and McCullough, 2020), so scientists expect severe impacts of the invasion in ash-dominated wetlands and – to a somewhat lesser extent — in forested stream systems’ riparian areas (Engelken and McCullough, 2020). They expect cascading impacts on 1) hydrology; 2) plant communities; 3) wildlife; 4) Native American cultures; and possibly even storage of carbon in vegetation and soils (Kolka et al. 2018).

1) Hydrology

Experiments suggest that loss of ash will cause higher water tables, especially during late summer and fall (Kolka et al 2018). This will result from reductions in evapotranspiration as large trees are replaced by shrubs and grasses (see below) (Kolka et al. 2018; Slesak et al. 2014). The higher water table might be exacerbated if higher annual precipitation levels predicted by climate change models occur. On the other hand, these models also predict a simultaneous increase in longer droughts, which might partially counteract higher precipitation and reduced evapotranspiration (Kolka et al. 2018). If they occur, these possible increases in drought length and frequency might enhance the establishment of less water-tolerant non-ash tree species in former black ash wetlands.

2) Plant Communities

Higher water tables are expected to reduce tree densities and promote conversion to open or shrub-dominated marshes. Several of the possible alternative tree species do not thrive as well as black ash under current conditions (Kolka et al. 2018). However, new hydrologic conditions might make forest restoration even more difficult because herbaceous plants transpire less water than trees, thus exacerbating the rising water tables (Slesak et al. 2014).

In upper Michigan, experiments which killed ash by cutting or girdling did not lead to an increase in growth rates of the remaining canopy species despite the increase in available resources (e.g., sunlight and nutrients) – presumably because of the raised water table (Kolka et al. 2081).

While some studies have found that black ash seedlings and saplings dominated the woody component of the swamp understory up to three years after ash were experimentally removed (Kolka et al. 2018), Engelken and McCullough (2020) found only eight saplings and a single seedling.

Scientists have planted several tree species in experiments to see which might be used to maintain the forested wetlands in the absence of black ash. The results are a confusing mix. Some species grew well once established – but had low levels of seedling establishment. Some trees planted on elevated microsites (hummocks) had the greatest survival and growth rates. (For specific data, see Kolka et al. 2018). A further consideration is tree species’ ability to adapt to warming temperatures already evident and expected to increase in coming decades (Slesak et al. 2014).

Consequently, Slesak et al. (2014) think it is likely that the EAB invasion will alter vegetation dynamics and cause a shift to an altered ecosystem state (e.g., open marsh condition) with higher water tables. They caution that the degree of ecosystem alteration will vary depending on site hydrology, annual precipitation, and period of time necessary for establishment of deeper rooted vegetation.

3) Wildlife

Moreover, any changes in vegetation will also affect the biota in more subtle ways through altered nutrient cycles. Black ash leaf litter is highly nutritious, having some of the highest nitrogen, phosphorus, and cation contents of any hardwood forest species (Kolka et al. 2018). Black ash leaves also decompose faster than most alternative tree species’ leaves (summary of Palik USDA Forest Service, here; Youngquist et al. 2018).

Youngquist et al. (2018) studied litter breakdown, litter nutritional quality, and growth of a representative invertebrate litter feeder – larvae of a shredding caddisfly (Limnephilus indivisus). They found that the larvae’s risk of death increased by a factor of three times or more when caddisflies were fed American elm, balsam poplar, or lake sedge leaves compared to black ash leaf litter. Even when the larvae lived – but matured more slowly because of the lower nutrition value of the leaves – they would still be vulnerable because they must reach metamorphosis before pond dry-down. In any planting done to maintain forested quality of wetlands, need to consider the nutritional quality of the leaf litter provided by replacements. Speckled alder was only apparently acceptable substitute; it was second to black ash in acceptability to caddisflies (Youngquist et al. 2020)

In fact, Youngquist et al. (2020) concluded that plant and detritivore biodiversity loss due to EAB invasion could alter productivity and decomposition at rates comparable to other anthropogenic stressors (e.g., climate change, nutrient pollution, acidification). The result will be altered biogeochemical cycles, resource availability, and plant and animal communities.

Scientists are also concerned about the impact of ash tree mortality on forest connectivity. Conversion of wooded swamps to shrub-and sedge-dominated wetlands will result in the loss of important micro-habitats that are already limited across the forested landscape and may also reduce availability of critical habitat for migrating birds. These changes will exacerbate on-going changes in land use in the Great Lakes region that are causing loss of forest habitat and forest homogenization. As yet, the magnitude of the impact on wildlife is unclear (Kolka et al. 2018).

black ash baskets – displayed at 2006 conference
photo by Faith Campbell

4) Cultural importance – baskets

Native Americans living in the range of black ash have utilized the wood to make baskets and other tools for thousands of years. Baskets had numerous uses, such as packs for carrying items, fish traps, and for preparing food and storing household items. Ash items also had ceremonial uses and they are highly sought as gifts and in trade. The skill needed to select a good tree and work the wood is handed down through the generations and is an important part of tribes’ culture (Benedict 2010).

Discussion of these cultural traditions can be found as Powerpoints here and here.

A video is posted here.

USFS Research Efforts

Concerned by the spread of EAB and probable impact on black ash swamps, the USDA Forest Service has initiated major research studies with the goal of filling in the numerous knowledge gaps and developing management recommendations. A large-scale study using various manipulations to simulate the EAB invasion was initiated in the Chippewa National Forest in northern Minnesota in 2009. A companion study began in the Ottawa National Forest in Michigan in 2010 (Kolka et al. 2018). The Slesak, Youngquist, and Kolka publications cited in this blog report results of some of the studies in this project. Other studies of black ash conditions, including regeneration, at various stages of the EAB invasion wave are being carried out by Deb McCullough, Nate Siegert, and others. They are working at sites from Michigan to New England (D.G. McCullough, pers. comm.).

Posted by Faith Campbell

For a great discussion of black ash basketweavers, see Anne Bolen, A Silent Killer: Black Ash Basket Makers are Battling a Voracious Beetle to Keep their Heritage Alive, American Indian Magazine, Spring 2020, available here.

SOURCES

Benedict, M. 2010. Ecology and the Cultural and Economic Importance of Black ash (Fraxinus nigra Marsh) for Native Americans May 2010 https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5191796.pdf

Engelken, P.J. and D.G McCullough. 2020. Riparian Forest Conditions Along Three Northern Michigan Rivers Following Emerald Ash Borer Invasion. Canadian Journal of Forest Research. Submitted

Kolka, R.K., A.W. D’Amato, J.W. Wagenbrenner, R.A. Slesak, T.G. Pypker, M.B. Youngquist, A.R. Grinde and B.J. Palik. 2018. Review of Ecosystem Level Impacts of Emerald Ash Borer on Black Ash Wetlands: What Does the Future Hold? Forests 2018, 9, 179; doi:10.3390/f9040179 www.mdpi.com/journal/forests

Slesak, R.A., C.F. Lenhart, K.N. Brooks, A.W. D’Amato, and B.J. Palik. 2014. Water table response to harvesting and simulated emerald ash borer mortality in black ash wetlands in MN, USA. Can. J. Forestry. Res. 44:961-968.

Youngquist, M.B., C. Wiley, S.L. Eggert, A.W. D’Amato, B.J. Palik, & R.A. Slesak. 2020. Foundation Species Loss Affects Leaf Breakdown and Aquatic Invertebrate Resource Use in Black Ash Wetlands. Wetlands. Society of Wetland Scientists

Posted by Faith Campbell

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

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/

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.

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.

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