March 2021 – Center for Invasive Species Prevention

Asian longhorned beetle – Eradication in South Carolina will be Extremely Difficult

arrows indicate red maples in the swamps of ALB regulated site in South Carolina
photo by David Coyle

The Asian longhorned beetle (ALB) is one of the most threatening of the hundreds of non-native insects and pathogens introduced to American forests since European colonization began 400 years ago. The ALB attacks about 100 species of trees in 12 or 13 genera; it prefers maples, poplars, willows, and elms. Forests with substantial components of susceptible species constitute 10% of forests on the U.S. mainland and nearly all of Canada’s hardwoods. Host trees species also make up a significant proportion of trees in urban areas. A two-decade old estimate is that ALB could cause more than $1.2 billion in damage to urban trees [Coyle et al. 2021; full citation at the end of the blog]. The contemporary estimate would be higher.

The ALB began showing up in imports and in warehouses less than a dozen years after the U.S. opened trade with China [see Chapter 3 of Fading Forests II; url provided at the end of this blog]. Now there is a new infestation in South Carolina that threatens to be the most difficult to eradicate. Given the level of resources and extended commitment this will demand from APHIS and South Carolina, I worry that the agencies and Congress will give up. To find more money, will the agency take funds from other pests that also need to be addressed? Will it seek – and receive – emergency funding? Congress is currently considering funding for APHIS for the fiscal year that begins in October. Let’s inform them of the need to ensure adequate resources to carry forward necessary eradication efforts.

ALB in the U.S.: 25 Years of Repeated Infestations and Eradications

The first established ALB population to be detected was that in Brooklyn, New York, in 1996. Since then, seven more outbreaks have been detected in the United States [Poland et al. 2021; South Carolina press release] plus two in Canada. Several populations have been eradicated: a single population in Illinois, several populations in New Jersey, three populations in New York; a small outlying population in Ohio (APHIS newsletter Feb 2021); and two Canadian outbreaks.

Despite the U.S. and Canada having adopted regulations requiring treatment of wood packaging from China effective January 1999, ALB larvae continue to be detected in wood packaging from that country. 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. 2020 – full citation at the end of the blog).

Port of Charleston; photo by Walter Lagrenne, South Carolina Port Authority

ALB Near Charleston, S.C.: Recently Detected; Must be Eradicated

The most recent detection is near Charleston, South Carolina. As usual, a beetle was found by a member of the public. Dendrological studies indicate that this infestation was seven years old at the time of its detection in May 2020, meaning it began about 2013 (Coyle et al. 2021). As the authors note, it has proved impossible to determine whether the South Carolina outbreak resulted from transport of infested wood from the Ohio outbreak or from China directly. Lots of visitors travel from the Midwest to South Carolina every winter. The center of the primary area of infestation includes a railway and an RV park which might be utilized by such travelers. On the other hand, two ports that receive high volumes of incoming shipping containers including wood packaging are nearby — Charleston, SC and Savannah, GA (Coyle et al. 2021). Charleston imported almost 666,000 containers (measured as 20-foot equivalents, or TEUs) in 2013.

Even under the best circumstances, eradicating an ALB infestation is difficult. Eradicating the Chicago outbreak took ten years [Poland et al. 2021]; eradicating the Brooklyn infestation took 23 years [APHIS ALB newsletter]. Massachusetts might be on the verge of eradicating the Worcester outbreak twelve years after it was detected because only one infested tree was found in 2020 [Felicia Hubacz at Northeast Forest Pest Council meeting, March 2021]

Eradication entails removing large numbers of trees – more than 171,000 in the Northeast and Midwest; and pesticide treatment of at least 800,000 [Poland et al. 2021]. Tens of thousands of trees must be inspected – especially in areas with significant woodland areas like the South Carolina site. In Clermont County, Ohio, 3,500,000 trees have been surveyed in the regulated area – which is 56 square miles [APHIS newsletter]

In South Carolina, APHIS and the state are already regulating 72.6 mi² — and that is before the full extent of the infestation has been delimited. This regulated area is larger than the Ohio and New York regulated areas, although smaller than that in Massachusetts (110 mi² Coyle et al.). As of February 2021, 4,425 infested trees have been identified (APHIS newsletter]. Ninety-eight percent are red maples; half of the others are willows (Coyle et al.) In May 2021, APHIS expanded the quarantine zone to 76.4 square miles (APHIS press release May 21, 2021).

So APHIS and South Carolina face a great deal of hard work. But acreage and numbers of trees affected don’t convey the real extent of the challenge.

The first challenge is anticipating the timing of events in the ALB life cycle. Scientists understand a great deal about the ALB life cycle. However, that knowledge all applies to areas with temperate climates such as the U.S. northeast, southern Canada, and Europe. South Carolina has a subtropical climate. How will the warmer climate affect the beetle’s speed of development, timing of emergence, etc. Already, dendrologial studies indicate that the ALB in South Carolina might complete development from egg to mature adult much faster – in less than a year rather than one to four years (Coyle et al.)

working conditions in the South Carolina swamps;
photo by David Coyle

An even bigger challenge will be trying to carry out searches for infested trees and standard responses. Removing infested trees and removing or applying pesticides to at-risk host trees is standard practice. Much of the regulated area has standing water and/or saturated soil. These conditions – plus the presence of venomous snakes and alligators – make visual surveys from the ground or by tree climbers difficult. Use of lifts and bucket trucks will be impossible. When infested trees are found, felling trees in swampy conditions presents a heighted risk for felling crews. And it will be impossible to operate the equipment needed to remove or chip infested trees (Coyle et al.). I believe it is impossible to use soil injection to treat at-risk trees under such conditions.

SOURCES

Coyle, D.R., R.T. Trotter, M.S. Bean, and S.E. Pfister. 2021. First Recorded Asian Longhorned Beetle (Coleoptera: Cerambycidae) Infestation in the Southern United States. Journal of Integrated Pest Management, (2021) 12(1): 10; 1–6

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

Poland, T.M., T. Patel-Weynand, D.M. Finch, C.F. Miniat, D.C. Hayes, V.M. Lopez. 2021. Invasive Species in Forests and Rangelands of the United States. Springer.

USDA APHIS Asian longhorned beetle monthly newsletter for March 2021. Sign up here https://www.aphis.usda.gov/aphis/resources/pests-diseases/asian-longhorned-beetle/ALB-eNewsletter

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

Pests in Northeastern Forests: What’s Alarming, What’s Not

map showing spread of beech scale, which facilitates beech bark disease

I recently participated in the 2021 annual meeting of the Northeast Forest Pest Council (virtual, of course). Speakers – most of them from state forestry agencies, but including students – presented a disturbing picture. Numerous established insects and diseases continue to spread. In some cases, they are resurging after weather-caused slow-downs. There are also a few bright spots.

The Alarming

To me the most alarming situation is that for American beech – because all three threats continue to expand.

Beech bark disease Since 2000, BBD has spread across southern Quebec into Ontario, Michigan, and Wisconsin; the Blue Ridge in Virginia; and central New Jersey.

Beech leaf disease Originally discovered near Cleveland in 2012, BLD has been spreading, primarily eastward.

BLD was detected for the first time in Massachusetts, in Plymouth and Bristol counties (on the coast North of Cape Cod). It might also be in Worcester. Both American and European beech trees of all sizes are affected; some of the largest are “on the verge” of death. (Felicia Hubacz)

The first detections in New Jersey are in Bergen and Essex counties – bordering southern New York. Both detections were by members of the public. Rosa Yoo says there is confusion about which state agency has the lead, so no official notices have been published (although the detection is recorded on the map). She hopes to establish long-term monitoring plots.

West Virginia now says that BLD is present in Tomlinson Run State Park in Hancock County. Kristen Carrington plans to focus detection efforts on the state’s norther panhandle which rises along the Pennsylvania border. She has established seven long-term monitoring plots.

Meanwhile, states where BLD was detected earlier continue to add new counties to the list of those infested. In New York, five new counties have been recorded. All the New York State finds have been on public lands, so the map doesn’t present the full picture (Carlson). In Connecticut, the disease is in all coastal counties and is more scattered in inland areas. Connecticut has set up some long-term monitoring plots. (Stafford)

New York is also trying to identify insect species associated with beech trees and beech litter – as a first step in trying to determine whether any vector the nematode that is thought to cause the disease. I suggest that it is also useful to understand which arthropod species might be at risk as beech decline. Don’t folks often lament the lack of this information for chestnut? Aren’t scientists praised for compiling initial lists for insects associated with ash?

Beech leaf mining weevil According to Jeff Ogden of the Nova Scotia Department of Lands and Forestry, this weevil has defoliated trees on 5987 hectares. First detected near Halifax in 2012, the weevil is now found throughout Nova Scotia. Some trees near Halifax have died. Ogden believes the weevil could be spread on movement of logs with bark and leaf litter. Camping is very popular in Nova Scotia, so the firewood risk appears real.

Also alarming is the resurgence of hemlock woolly adelgid across the region. HWA had been suppressed for a few years by harsh winters, but that reprieve is over. HWA is in 52 of 55 West Virginia counties (Kristen Carrington). Newly detected outbreaks are found across Pennsylvania and in the Adirondacks of New York. HWA continues to spread north – slowly – in New Hampshire and Vermont. In Nova Scotia, the outbreak detected in 2018 is spreading slowly to the West (Jeff Ogden).

All states are releasing a variety of biocontrol agents, often Laricobius nigrinus but also L. osakensis. Various agents have been released for decades — for example, Connecticut has released more than 125,000 agents over more than 20 years. I do hope the two Laricobius beetles prove to be more effective in controlling the agelgid.

Several states note that elongate hemlock scale (Fiorinia externa) is now at least as damaging as the adelgid.

Pennsylvania is growing hemlocks for restoration purposes; New Jersey has begun a similar program. See my earlier blog about efforts to breed hemlocks resistant to the adelgid, available here.

Spotted lanternfly is now established in nine states — from Ohio and West Virginia to Connecticut. It continues to spread. In the longer-established infestation areas of southeastern Pennsylvania, black walnut has been severely damaged by early instar larvae. In New Jersey, eight counties are under quarantine, but the insect has been detected much more broadly. The newest state is Connecticut, which found populations in several counties and is drafting quarantine regulations. Massachusetts, Maine, and Vermont have found some egg masses or evidence of infestation on goods entering from Pennsylvania, but not yet an established population.

The Not So Alarming — but Still Concerning

Asian Longhorned Beetle Massachusetts is consistently finding fewer trees infested by the ALB. In 2020, they found only one! It was isolated in the middle of a golf course. Intensive surveys and trapping in the vicinity found no other infested tree.

This is great news! However, I worry that resources will be withdrawn too soon – especially with APHIS’ need to fund an eradication program for the same pest in a swampy forest area in South Carolina where it will be difficult to work. Already Massachusetts reported that it has fewer traps and staff, and some difficulties accessing the lure.

Early Detection Efforts

New Jersey and West Virginia have carried out surveys of sassafras stands for the redbay ambrosia beetle (also here). West Virginia is also surveying for Phytophthora ramorum (the sudden oak death pathogen) and walnut twig beetle (vector of thousand cankers disease). Funding for surveys of the former probably came from USFS Forest Health Protection; for the latter, from APHIS. I applaud these “early detection” efforts.

Too Late for “Early Detection” but Getting Welcome the Attention

New Hampshire noted rising concern about Jumping worms. The state has received 48 complaints since 2017; 43 of these were in 2020. This led to a spirited discussion about invasive worms’ impacts. Don Eggen noted that concern focuses on soils in unglaciated regions. Non-native worms can destroy the duff layer. Most of the research has been carried out in the Midwest. See my earlier blogs about invasive earthworms here.

Tim Tomon reported that the USFS Morgantown WV research office has sampled the Allegheny NF. They have found other invasive earthworms but not jumping worms. Rosa Yoo of New Jersey alerted participants to the jumping worm research and management group – JWORM

Other Updates

Beech leaf disease

The USDA Forest Service has published a Pest Alert on BLD. Google it now. When a url becomes available I will update this notice. The flyer includes contact information for a site that provides both detection training and a place to record your finds.

Sudden Oak Death

The EU1 strain was detected in forest trees in Del Norte County, California in autumn 2020. This detection was both the first officially confirmed detection of P. ramorum in Del Norte County and the first detection of the EU1 strain in forest trees in California. The source is unclear. The nearest infestation is 12 miles away, along the Winchuk River in Curry County, OR; those trees are infected with the NA1 strain. The nearest known EU1 infestation is about 35 miles away. The site of the California EU1 infestation has minimal California bay laurel (Umbellularia californica). This detection has led to designation of Del Norte County as officially infested; it becomes the 16^th California county so designated. [Information from the California Oak Mortality Task Force newsletter for December 2020, available here.]

Posted by Faith Campbell

Congressional Action to Protect Trees from Non-Native Pests

Rep. Peter Welch of Vermont has reintroduced his bill to improve programs intended to prevent introduction of non-native forest pests and enhance efforts to reduce their impacts. The latter provisions include support for breeding trees resistant (or tolerant) to the pest. I hope H.R. 1389 will be adopted – then spur new efforts to conserve and restore forest trees! Please follow my suggestion below.

The Invasive Species Prevention and Forest Restoration Act H.R. 1389 is co-sponsored by Reps. Brian Fitzpatrick (PA), Annie Kuster & Chris Pappas (NH), and Elise Stefanik (NY).

For updates, visit https://www.congress.gov/search?q={%22congress%22:[%22117%22],%22source%22:%22all%22,%22search%22:%22HR%201389%22}&searchResultViewType=expande

When he introduced the bill, Rep. Welch said

“Invasive species are devastating to forests which are a central part of Vermont’s economy and our way of life. This bill will fund efforts to revitalize damaged forests and highlight the need for making this a priority within the federal government.”

Major provisions of H.R. 1389:

Expands USDA APHIS’ access to emergency funding to combat invasive species when existing federal funds are insufficient and broadens the range of actives that these funds can support.
Establishes a grant program to support institutions focused on researching methods to restore native tree species that have been severely damaged by invasive pests.
Authorizes funding to implement promising research findings on how to protect native tree species.
Mandates a study to identify actions needed to overcome the lack of centralization and prioritization of non-native insect and pathogen research and response within the federal government, and develop national strategies for saving tree species.

As I have described in earlier blogs, the measures adopted by federal and state governments to prevent non-native pathogen and insect pest introductions – and the funding to support this work – have been insufficient to meet the growing challenges. In just the past decade, several new tree-killing pests have been detected: polyphagous and Kuroshio shot hole borers, spotted lanternfly, two rapid ʻōhiʻa death pathogens, Mediterranean oak beetle, velvet longhorned beetle. Over the same period, the Asian longhorned beetle has been detected in Ohio and South Carolina; the emerald ash borer expanded its range from 14 to 35 states; the redbay ambrosia beetle and its associated fungus spread from five states to 11; a second strain of the sudden oak death fungus appeared in Oregon forests; and whitebark pine has been proposed by the US Fish and Wildlife Service for listing as Threatened under the Endangered Species Act.

During this same period, funding for the USDA Forest Service Forest Health Protection program has been cut by about 50%; funding for USFS Research projects targetting 10 high-profile non-native pests has been cut by about 70%.

One reason for this disconnect between need and resources is that the non-native tree pest problem is largely out of sight and therefore does not lend itself to the long-term public attention needed to remediate the threats. It is up to us to raise the political profile of these issues.

On the positive side, the passage of time has brought forth new solutions, a deeper understanding of the genetics of plants and animals, new measures for igniting public awareness and invasive identification, new technologies and strategies for helping trees adapt, and a recognition of what resources and organization it will take to mount a proper solution to the problem.

“Project CAPTURE” (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation) has proposed priority species for enhanced conservation efforts. Top priorities in the continental states are listed below. A separate study is under way for forests in Hawai`i, Puerto Rico, and U.S. Virgin Islands.

Florida torreya (Torreya taxifolia)
American chestnut (Castanea dentata)
Allegheny chinquapin (C. pumila)
Ozark chinquapin (C. pumila var. ozarkensis)
redbay (Persea borbonia)
Carolina ash (Fraxinus caroliniana)
pumpkin ash (F. profunda)
Carolina hemlock (Tsuga caroliniana)
Port-Orford cedar (Chamaecyparis lawsoniana)
tanoak (Notholithocarpus densiflorus)
butternut (Juglans cinerea)
eastern hemlock (Tsuga canadensis)
white ash (Fraxinus americana)
black ash (F. nigra)
green ash (F. pennsylvanica).

For a brief explanation of Project CAPTURE, see my earlier blog here. For an in-depth description of the Project CAPTURE process and criteria for setting priorities, read Potter, K.M., M.E. Escanferla, R.M. Jetton, and G. Man. 2019. Important Insect and Disease Threats to United States Tree Species and Geographic Patterns of Their Potential Impacts. Forests 2019, 10. https://www.fs.usda.gov/treesearch/pubs/58290

Please ask your representative to co-sponsor H.R. 1389. Please ask your senators to sponsor a companion bill. For more information, contact Alex Piper at Alex.Piper@mail.house.gov or 202-306-6569 .

H.R. 1389 is endorsed by Vermont Woodlands Association, American Forest Foundation, Center for Invasive Species Prevention, the Reduce Risk from Invasive Species Coalition,, Entomological Society of America, and North American Invasive Species Management Association.

Posted by Faith Campbell

Status of the Spotted Lanternfly – Threatening Crops & – Possibly – Forest Trees

spotted lanternfly; photo by Holly Raguza, PA Department of Agriculture

Environmental Entomology, in partnership with other journals from the Entomological Society of America, has published a special collection of papers on the spotted lanternfly, Lycorma delicatula. All papers in the collection are freely available to read and download through February 16, 2022. I will summarize key points, with brief references to the specific article.

The papers are available at https://academic.oup.com/ee/pages/research-on-spotted-lanternfly

Areas at Risk

As this map shows, the spotted lanternfly (SLF) is thought able to establish in more than 26 states.

Source: T.T Wakie et al., 2020. The Establishment Risk of Lycorma delicatula (Hemiptera: Fulgoridae) in the United States and Globally. Journal of Economic Entomology, Volume 113, Issue 1, February 2020, Pages 306-314, https://doi.org/10.1093/jee/toz259

Host Trees

SLF prefers the invasive tree species, Tree of Heaven (Ailanthus altissima), especially for oviposition. Ailanthus is widespread, so this is not very limiting. However, the SLF can complete its life cycle in the absence of this host. [O. Uyi et al. 2020. Spotted Lanternfly (Hemiptera: Fulgoridae) Can Complete Development and Reproduce Without Access to the Preferred Host, Ailanthus altissima. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1185–1190, https://doi.org/10.1093/ee/nvaa083]

Spotted lanternflies have been recorded as feeding on at least 56 plant species in North America and 103 plant species worldwide; most are shrubs, trees, or stout vines. [L. Barringer and C.M. Ciafré. 2020. Worldwide Feeding Host Plants of Spotted Lanternfly, With Significant Additions From North America. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 999–1011, https://doi.org/10.1093/ee/nvaa093]

SLF aggregates on tree-of-heaven by its adult stage. However, egg masses are found on 24 types of substrates with tree-of-heaven, black cherry, black birch, and sweet cherry. [H. Liu. 2019. Oviposition Substrate Selection, Egg Mass Characteristics, Host Preference, and Life History of the Spotted Lanternfly (Hemiptera: Fulgoridae) in North America. Environmental Entomology, Volume 48, Issue 6, December 2019, Pages 1452–1468, https://doi.org/10.1093/ee/nvz123]

An evaluation of spotted lanternfly survivorship on 26 host plant species in 17 families found that eight species supported development from first instar to adult: black walnut, chinaberry, oriental bittersweet, tree-of-heaven, hops, sawtooth oak, butternut, and tulip tree. When offered a choice between black walnut and tree-of-heaven, nymphs showed no preference; adults showed a significant preference for tree-of-heaven. [K. Murman et al. 2020. Distribution, Survival, and Development of Spotted Lanternfly on Host Plants Found in North America. Environmental Entomology, Volume 49, Issue 6, December 2020, Pages 1270–1281, https://doi.org/10.1093/ee/nvaa126]

Dispersal

Spotted lanternfly nymphs (all instars) usually moved only short distances over a 7-day period, but a few were discovered 50-65 meters away. [J.A. Keller et al. 2020. Dispersal of Lycorma delicatula (Hemiptera: Fulgoridae) Nymphs Through Contiguous, Deciduous Forest. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1012–1018, https://doi.org/10.1093/ee/nvaa089]

Detection – Traps & Lures

A test of 43 host plant volatiles found 11 to be significantly attractive. [N.T. Derstine et al. 2020. Plant Volatiles Help Mediate Host Plant Selection and Attraction of the Spotted Lanternfly (Hemiptera: Fulgoridae): a Generalist With a Preferred Host. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1049–1062, https://doi.org/10.1093/ee/nvaa080]

A comparison of several trap types found that circle traps caught more SLF than sticky bands, and fewer non-target organisms. Traps placed on the trunks of trees caught more SLF than traps placed in the tree canopy. [J.A. Francese, et al. 2020. Developing Traps for the Spotted Lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae). Environmental Entomology, Volume 49, Issue 2, April 2020, Pages 269–276, https://doi.org/10.1093/ee/nvz166] In one study, addition of a lure containing methyl salicylate did not increase captures. [L.J. Nixon, et al. 2020. Development of Behaviorally Based Monitoring and Biosurveillance Tools for the Invasive Spotted Lanternfly (Hemiptera: Fulgoridae). Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1117–1126, https://doi.org/10.1093/ee/nvaa084] his contradicted an earlier study that suggested that traps with high release methyl salicylate lures did capture more SLF. [M.F. Cooperband, et al. 2019. Discovery of Three Kairomones in Relation to Trap and Lure Development for Spotted Lanternfly (Hemiptera: Fulgoridae). Journal of Economic Entomology, Volume 112, Issue 2, April 2019, Pages 671–682, https://doi.org/10.1093/jee/toy412]

Potential Controls: Parasites, Parasitoids, and a Pathogen

Significant efforts are afoot to find possible biocontrol agents. Scientists have surveyed SLF and associated parasites/parasitoids across 27 provinces and administrative regions of China from 2015 to 2019. They recovered an egg parasitoid, Anastatus orientalis, and a nymphal parasitoid, Dryinus sinicus, and are studying these further as potential biological control agents of spotted lanternfly. [B. Xin et al. 2020. Exploratory Survey of Spotted Lanternfly (Hemiptera: Fulgoridae) and Its Natural Enemies in China Environmental Entomology, nvaa137, https://doi.org/10.1093/ee/nvaa137]

The egg parasitoid Anastatus orientalis has the advantages of being easy to rear and long lived. Research is under way to tests its host specificity. [H.J. Broadley et al. 2020. Life History and Rearing of Anastatus orientalis (Hymenoptera: Eupelmidae), an Egg Parasitoid of the Spotted Lanternfly (Hemiptera: Fulgoridae). Environmental Entomology, nvaa124, https://doi.org/10.1093/ee/nvaa124]

The spotted lanternfly leaves behind a chemical trail when walking – a trail which the parasitoid wasp Anastatus orientalis uses to locate the host’s eggs. [R. Malek et al. 2019. Footprints and Ootheca of Lycorma delicatula Influence Host-Searching and -Acceptance of the Egg-Parasitoid Anastatus orientalis [Environmental Entomology, Volume 48, Issue 6, December 2019, Pages 1270–1276, https://doi.org/10.1093/ee/nvz110]

The established gypsy moth egg parasitoid Ooencyrtus kuvanae has been observed attacking SLF egg masses in the field. [H. Liu and J. Mottern. 2017. An Old Remedy for a New Problem? Identification of Ooencyrtus kuvanae (Hymenoptera: Encyrtidae), an Egg Parasitoid of Lycorma delicatula (Hemiptera: Fulgoridae) in North America. Journal of Insect Science, Volume 17, Issue 1, January 2017, 18, https://doi.org/10.1093/jisesa/iew114]

Single applications of the insect pathogenic fungus Beauveria bassiana strain GHA killed 43-48% of spotted lanternflies on preferred host plants in a park. Adult spotted lanternflies feeding on potted grapevines were sprayed with the same fungus, resulting in 100% mortality after 9 days. [E.H. Clifton, et al. 2020. Applications of Beauveria bassiana (Hypocreales: Cordycipitaceae) to Control Populations of Spotted Lanternfly (Hemiptera: Fulgoridae), in Semi-Natural Landscapes and on Grapevines Environmental Entomology, Volume 49, Issue 4, August 2020, Pages 854 – 864, https://doi.org/10.1093/ee/nvaa064]

Ambrosia Beetles: Not All the Same (laurel wilt v. shot hole borers)

Horton House on Jekyll Island, Georgia – when the redbays were still alive!
photo by Faith Campbell

A recent USFS book on invasive species reports that at least 58 species of bark and ambrosia beetles have been established in the US. Recent studies highlight very different situations due to two invasive ambrosia beetles. Here are summaries of each.

1. Laurel Wilt: Unmitigated Disaster in Atlantic and Gulf Coastal Plains – and Possibly More Widely

The disease laurel wilt, caused by the pathogen Raffaelea lauricola and vectored primarily by the redbay ambrosia beetle (Xyleborus glabratus) presents a dire contrast. (For this section, see Olatinwo, Fraedrich & Mayfield. 2021; full reference at end of the blog.) In the nearly 20 years since its first detection near Savannah, Georgia in 2002, laurel wilt has spread across more than 100 counties and parishes in 11 states from North Carolina south through Florida, west to eastern Texas, and as far northward as Kentucky.

Laurel wilt has killed hundreds of millions of trees in the plant family Lauraceae. Approximately 13 Lauraceae species in eight genera (depending on taxonomic proclivities!) are indigenous to the U.S. Individual species’ vulnerability appears to depend largely on size; the beetle is attracted to vertical stems of a certain diameter. As a result, the native tree species redbay (Persea borbonia), swampbay (Persea borbonia var. pubescens or P. palustris), and more recently sassafras (Sassafras albidum) have experienced the most damaging attacks. Also heavily attacked has been the commercial avocado (Persea americana) which is native to Central America.

While redbay is widespread in a defined geographic area – a long the Atlantic and Gulf Coastal Plain from North Carolina to Texas, sassafras is subcontinental: it is found in 28 states, 53 ecoregions, and 69 forest types. Approximately 80% of sassafras in affected areas have been killed. In recent years, spread has proceeded by many “jumps” to disjunct areas where sassafras occurs in isolation from other hosts. At present, approximately 52% of the range of sassafras might experience winter temperatures sufficiently cold to cause significant mortality of the redbay ambrosia beetle. However, this temperature protection is likely to decline to about10% of sassafras’ range as a result of even modest climate change (a 1.4 °C increase in winter minimum temperatures).

The ecological impact of loss of redbay and sassafrass are not clear. Both are sources of wildlife food. The principal specialist on redbay is the Palamedes swallowtail butterfly (Papilio palamedes), which is also the primary pollinator of a rare plant, yellow-fringed orchid. The rapid loss of swampbay on tree islands in the Everglades could facilitate establishment of even more individuals of the already widespread invasive plant species Brazilian pepper (Schinus terebinthifolius) or Melaleuca quinquenervia.

Other U.S. native plant species in the Lauracea family are apparently partially protected by the small diameter of their stems, which the beetle doesn’t find acceptable. These include – in the Southeast — the federally listed pondberry (Lindera melissifolia), “species of interest” pondspice (Litsea aestivalis), bog spicebush (Lindera subcoriacea), pepperleaf sweetwood (Licaria trianda), lancewood (Ocotea coriacea), and love-vine (Cassytha filiformis). The common shrub spicebush (Lindera benzoin) might be protected by its possession oflower quantities of the primary host volatile attractant. On the other hand, the widespread Pacific state shrub California laurel or Oregon myrtle (Umbellularia californica) is considered highly vulnerable, should laurel wilt be moved there in wood, mulch, or nursery plants.

Laurel wilt poses an unknown threat to the many plant species in the Lauraceae in Central and South America (750 species), Australia (125 species), Madagascar (135 species), and the Macaronesian Islands off the coasts of Europe and Africa – the Azores, Canary Islands, and Madeira. The commercial spice bay laurel (Laurus nobilis) is native to the Mediterranean region (and planted elsewhere, including in the US). However, its small size, discontinuous distribution and isolation from other lauraceous host species might prevent development of a widespread epidemic.

The authors note the absence of effective measures to manage laurel wilt 20 years after its detection. They recommend restricting long-distance movement of infested wood, associated public awareness efforts, development and deployment of resistant hosts, silviculture (sanitation), targeted application of preventive chemical treatments for protecting high-value trees, and severing root grafts in avocado orchards and sassafras clones. They note that success will be dependent on sustained funding and a commitment to long-term area-wide implementation.

[As I noted in past blogs about APHIS deregulating the emerald ash borer, it is now up to the states to regulate movement of firewood. The lead will continue to be the non-governmental “Don‘t Move Firewood” campaign. The message will continue to encourage the public to buy firewood where they burn it and to refrain from moving firewood from areas that are under Federal quarantine for other pests of firewood (e.g., Asian longhorned beetle). This campaign and the new National Plant Board guidelines stress that firewood is a high-risk pathway for many pests of national or regional concern; they do not focus on any particular species. Leigh Greenwood, director of Don’t Move Firewood, thinks this is a good approach.]

Mayfield adds that the spread northwards on sassafras means that state diagnostic pathology labs should familiarize themselves with protocols for isolating the laurel wilt pathogen.

As to developing resistant varieties of redbay, I note that Potter et al. 2019 ranked redbay as fifth species highest in priority for genetic conservation and restoration breeding efforts. However, it is my impression that few federal resources have been allocated to such an effort on behalf of redbay.

2. Ambrosia beetles in California

At least 22 of the recently-established ambrosia and bark beetles are in California. Heavily urbanized southern California appears to be particularly vulnerable to such introductions. The proximity of ship traffic and associated cargo, as well as the great diversity of potential hosts in the area’s urban forests, are likely to blame.

Two such pests are the polyphagous (PSHB) and Kuroshio (KSHB) shot hole borers [collectively, invasive shot hole borers (ISHB)]. John Boland has studied the KSHB outbreak in the Tijuana River estuary intensively since 2015. Two recent studies – 2019 and 2021– demonstrate the importance of ecological and tree-related factors in determining the severity of attack by this ambrosia beetle. See references at the end of the blog.

The most susceptible site is wet and nutrient enriched (in the case of the Tijuana River, due to pollution).

The most susceptible trees are young, fast growing, and have thin bark (allowing KSHB access) and wood of low density and high moisture content (providing ideal conditions for KSHB and associated fungi).

willows killed by KSHB in Tijuana River estuary; photo by John Boland

As Boland has noted, all of these conditions occurred in the “wet” forests close to perpetual streams in the Tijuana River delta in 2015. These factors led to dramatic levels of mortality, which have not been equaled in other southern California deltas. In the five years from 2015 to 2020, the beetle/fungus complex infested an estimate 350,000 willows and killed an estimated 123,000 in a boom-and-bust cycle. Since 2016, the trees in the Tijuana River estuary have regrown to almost pre-infestation dimensions. (Boland is not certain why these new, fast-growing trees have not been attacked by the KSHB that remain in the area. He suggests that a local pathogen, parasite, parasitoid or predator is keeping the KSHB in check – although this has not been verified.)

Willows near the main river channel (“Wet Forest” units) cumulatively had a fatality rate of 39%. Strikingly, more distant “Dry Forest” units had a combined fatality rate of only 9%.

The 2019 study linked the higher rates of infestation, damage, and mortality that occurred in trees near the main river channel to the presence of year-round water that was often enriched by a heavy load of sewage. The trees respond by growing rapidly, resulting in thinner bark and less dense wood. The KSHB attacked in much higher numbers, impeding water transport and weakening the trees’ structure so that they were more easily broken during windstorms.

The 2021 study provided further detail. By comparing bark samples cut from 27 infested trees at the height of the infestation, in 2016 – 17, Boland and Woodward demonstrated thicker bark on the “Dry Forest” trees protected the trees by limiting the density of KSHB entry points. The fewer holes reduced internal structural damage to the trees, which allowed them to survive. Boland notes that the protection might arise from either the bark thickness itself, or higher quantities of protective chemicals.

Repercussions

The results suggest that a KSHB individual actively searches for a suitable tree and then searches for the thinnest bark on that tree in which to drill its hole.
Trees can recover from KSHB attack, indicating that the fungal symbionts are only moderately pathogenic at worst.
The ISHB are likely to cause much less damage than indicated by the one early model developed before these factors were understood. We need new models for ISHB spread and impact that incorporate these factors of site characteristics and host tree condition.

SOURCES

Boland, J.M. 2019. The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley Final Report. (Year 5) https://trnerr.org/wp-content/uploads/2020/05/KSHB-TRValley2020.pdf

Boland J.M. and D.L. Woodward. 2021. Thick bark can protect trees from a severe ambrosia beetle attack. PeerJ 9:e10755 https://peerj.com/articles/10755/

[all of Boland’s reports and articles on the KSHB are available at: The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley — Tijuana Estuary : TRNERR]

Olatinwo, R.O., S.W. Fraedrich & A.E. Mayfield III. 2021. Forests 2021, 12, 181. Laurel Wilt: Current and Potential Impacts and Possibilities for Prevention and Management

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/ j.gecco.2019.e00622.

Posted by Faith Campbell