Emerald Ash Borer Populations Research Articles

Status of ash forests and regeneration a decade after first detection of emerald ash borer infestation in New York state

In many forest stands, persistence of mature ash (Fraxinus spp.) and the ability of regenerating ash to reach maturity is likely to influence future forest composition and ecosystem structure. Seedlings and saplings are often too small to be infested by the initial wave of invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire, and low release numbers and a lagged response of introduced biological control agents in outbreak EAB populations make quick protection of mature trees unpredictable but may provide protection for the next generation of ash. This study reports current composition and status of historically ash-dominated forest stands in eastern and western New York a decade after first EAB detection and nine years after release of parasitoid wasps for biological control. Monitored trees exhibited an increasingly binary status over the study period with the death of almost all trees that initially showed signs of decline, leaving only healthy individuals with full canopies alive. Near complete mortality of mature trees was observed in eastern New York, whereas a substantial number of mature trees persisted in western New York. There was little change in numbers of ash seedlings (<2.5 cm DBH) or saplings (≥2.5 cm DBH and < 10 cm DBH) between 2014 and 2021 in either region; however, density of the tallest seedlings (>1 m in height) increased significantly in eastern New York. Changes in overstory forest composition were mostly explained by loss of mature ash. These results provide hope for regenerating ash to grow into existing canopy gaps with the protection provided by continued presence of biological control agents.

Successful establishment, spread, and impact of the introduced parasitoid Spathius galinae (Hymenoptera: Braconidae) on emerald ash borer (Coleoptera: Buprestidae) populations in postinvasion forests in Michigan.

Spathius galinae is a larval parasitoid native to the Russian Far East that was approved for release in the United States in 2015 for biological control of the emerald ash borer (EAB), Agrilus planipennis, an invasive beetle from Asia responsible for widespread mortality of ash trees (Fraxinus spp.) in North America. From 2015 to 2017, 1,340-1,445 females of S. galinae along with males were released into each release plot, paired with a nonrelease control plot (1-12.5 km apart), at 6 postinvasion forested sites containing abundant pole-sized ash trees in Michigan. By 2018, S. galinae had spread to all but one control plot. Based on the first year that S. galinae was found in trees in each control plot and the distances of those trees to the parasitoid release point within each site, we estimated that S. galinae spread at 3.7 (±1.9) km per year after its initial releases in 2015. The proportion of sampled trees with S. galinae broods, brood densities within sampled trees, and parasitism of EAB larvae increased sharply in both control and release plots after the last field releases in 2017, with the highest parasitism rates (42.8-60.3%) in 2020. Life table analysis showed that S. galinae alone reduced EAB's net population growth rate by 35-55% across sites from 2018 to 2020. These results demonstrate that S. galinae has established an increasing population in Michigan and now plays a significant role in reducing EAB populations in the area.

Establishment and impacts of emerald ash borer (Coleoptera: Buprestidae) parasitoids released at early- and post-invasion sites.

Forest stands infested by emerald ash borer (EAB), Agrilus planipennis Fairmaire, experience extensive mortality of mature ash trees. Post-invasion woodlands commonly have a small contingent of mature lingering ash, an orphaned cohort of seedlings/saplings, and low EAB densities. To protect regenerating ash against rebounding EAB populations, a suite of biocontrol agents are being reared and released. USDA APHIS guidelines currently recommend the release of parasitoids into forests prior to overstory ash mortality at sites containing a variety of ash size classes and low to moderate but building EAB densities. To understand if biocontrol establishment and control of EAB is feasible in post-invasion sites, we assessed the establishment of parasitoids in 6 post-invasion forest stands in 2 regions of NY and compared EAB mortality in these stands to 2 regions where releases were conducted during the early-invasion phase. Results of parasitoid trapping indicates Tetrastichus planipennisi Yang established under both release strategies. Spathius galinae Belokobylskij & Strazanac was only released in post-invasion stands, where it was established successfully. Artificial EAB cohorts were established and life tables were constructed at 3 sites per region. EAB mortality due to T. planipennisi parasitism was similar under both release strategies 2 yr after release in post-invasion stands versus 8 yr after release in early-invasion stands. Combined mortality from T. planipennisi and woodpecker predation resulted in consistently low EAB reproductive rates. Future biocontrol releases could target forests identified as economically or ecologically important, regardless of whether EAB populations are increasing or have collapsed following initial invasion.

Temporal and spatial dynamics of the emerald ash borer invasion in Connecticut as shown by the native digging wasp Cerceris fumipennis (Hymenoptera: Crabronidae).

Detecting and monitoring populations of the invasive emerald ash borer (EAB) is crucial to successful management of the pest and evaluation of its ecological impacts. However, the beetle's cryptic habit makes accurate monitoring costly and time-consuming. Biosurveillance takes advantage of the foraging effort of a predatory wasp Cerceris fumipennis (Hymenoptera: Crabronidae). This native, solitary, ground-nesting hunting wasp hunts adult buprestid beetles to provision its brood cells. By intercepting the hunting wasps, we can learn which species of buprestids are in the surrounding forest. The resulting data provides information on the presence and relative abundance of invasive buprestids like EAB which can supplement other monitoring efforts. In this paper we share results of ten years of biosurveillance surveys of the EAB in Connecticut. Among 112 sites, we observed EAB populations; from first detection, through the population peak and then through to the population crash, matching patterns observed in other regions of the United States. We also observed the spread of the EAB relative abundance as it moved through the state following an invasion front starting in New Haven, Co. The average time from first detection to population crash was nine years. On average, populations peaked three years after first detection, and remained at peak levels for three to four years. Population decline was gradual and took another three to four years. Notably, no evidence of a second introduction to Connecticut was seen with proportional abundance increasing over time after expanding outward from the introduction point. These results corroborate other traditional monitoring efforts in the eastern U.S. and provide independent validation of predicted population dynamics in ash stands.

Factors Affecting Efficacy of Trunk-Injected Emamectin Benzoate to Manage Emerald Ash Borer

Background: Emerald ash borer (EAB), Agrilus planipennis, is an invasive wood-boring beetle that threatens ash trees (Fraxinus spp.) in the urban forest. Methods: We compared the efficacy at which 3 different injection systems deliver emamectin benzoate (EB) to the leaf canopy and protect trees. Two of the systems, Arborjet Tree I.V.™ and Rainbow Ecoscience Q-Connect™, used sixteen ports/m of trunk circumference, whereas the third system, Brandt enTREE® EB, used eight. Results: The two systems with more injection ports provided more uniform delivery of insecticide to the leaf canopy. Although all 3 injection systems provided excellent control for the first 2 years, only the 16-port injection systems provided protection for up to 3 years. The number of injection ports affected insecticide delivery because the sectorial structure of the ash vascular system limited lateral product diffusion. Additionally, over the course of an 8-year study, we found trunk injections of EB made in the spring provided better control of EAB than fall injections. Protection afforded by a 2013 application in our study failed by 2016 as EAB populations reached their peak. A second application in 2016 extended protection past the peak of EAB abundance through 2019. Conclusions: We conclude that when the same dose of EB is delivered, efficacy of the application is influenced by the number of injection ports used in the injection system, time of application, and the status of the local EAB population. Arborists need to be aware of these factors when planning their EAB management program.

Invasive Populations of the Emerald Ash Borer Agrilus planipennis Fairmaire, 1888 (Coleoptera: Buprestidae) in Saint Petersburg, Russia: A Hitchhiker?

Simple SummaryThe emerald ash borer (EAB) is an invasive beetle of Asian origin that has killed millions of ash trees in North America and Russia, with a devastating economic and ecological impact. In September 2020, EAB was detected for the first time in Saint Petersburg, Russia, notably killing ash trees. The invasion came from the eastern direction (Moscow) and became a significantly notable event for Saint Petersburg, famous for its historical parks. Moreover, Saint Petersburg is 120–130 km from the eastern EU borders of Estonia and Finland, with railway, motorway, and ferry connections. Currently, EAB is one of the most serious quarantine insect pests in the EU. There is a risk that the eventual EAB invasion could potentially extirpate European populations of ash. Currently, 95% are devastated by the invasive fungal disease ash dieback. Here, we investigated the development of EAB populations in Saint Petersburg, from its initial invasion (estimated year 2015), until 2021. We found that climatic conditions of north Russia do not favor the natural aerial spread of EAB. The two isolated populations were located, respectively, close to a motorway, and the Neva River (used for cargo shipping), implying that the insect spreads by transport vehicles, or “hitchhiking”. This could potentially lead to the eventual invasion of the EU by this serious, tree-killing beetle.The emerald ash borer (EAB), Agrilus planipennis, is an invasive beetle of East Asian origin that has killed millions of ash trees (Fraxinus spp.) in North America and Russia. In September 2020, EAB was detected in Saint Petersburg, a notable event for the metropolitan city. The aim of the present study was to investigate the occurrence and ecology of EAB in Saint Petersburg. The presence of two distinct enclave populations of EAB was revealed, each of which has, most likely, been established through separate events of “hitchhiking” via transport vehicles. Following the invasion, the further spread of EAB in Saint Petersburg was slow and locally restricted, most likely due to climatic factors. This spread by “hitchhiking” suggests that the possibility of the further long-distance geographic spread of EAB in the Baltic Sea region (the EU) is high, both by ground transport (120–130 km distance from EU borders) and ferries that transport cars across the Baltic Sea. In certain cases, the development of EAB on Fraxinus excelsior, based on the stem portion colonized, larval densities, number of galleries, exit holes, viable larvae, and emerged adult beetles, was more successful than in Fraxinus pennsylvanica trees. The observed relatively high sensitivity of F. excelsior to EAB, therefore, casts doubt on the efficacy and benefits of the currently ongoing selection and breeding projects against ash dieback (ADB) disease, which is caused by the fungus Hymenoscyphus fraxineus. Inventory, mapping, and monitoring of surviving F. excelsior trees infested by both ADB and EAB are necessary to acquire genetic resources for work on the strategic long-term restoration of F. excelsior, tackling the probable invasion of EAB to the EU.

Predicting the potential for spread of emerald ash borer (Agrilus planipennis) in Great Britain: What can we learn from other affected areas?

Societal Impact StatementEmerald ash borer (EAB) is thought to have arrived in North America and European Russia at least 10 years prior to detection. Despite heightened awareness that EAB could invade Great Britain (GB), detection in the early stages of establishment is difficult, and initial symptoms might be mistaken for Chalara ash dieback. Our results suggest that if partial resistance to EAB in Fraxinus excelsior does not significantly dampen EAB population dynamics, then EAB could establish and spread across large parts of southern England within a relatively short time period; however, further northern spread may be limited by the relatively cool climate.Summary The accidental introduction of emerald ash borer (EAB) to North America and European Russia in the 1990s has resulted in an ongoing crisis with millions of ash trees damaged and killed at immense economic and social cost. Improving our understanding of how rapidly the pest might spread should it enter Great Britain (GB) plays an essential part in planning for a potential outbreak. Two metrics are used to investigate the potential dynamics of EAB in GB: the observed rate of spread in the North American and Russian regions; and the relationship between degree days and emergence that may determine environmental suitability and whether the life cycle is univoltine or semivoltine. The pest is still spreading in North America and European Russia with an overall average rate of spread between 2002 and 2018 of approximately 50 km a year. Early detection of the pest is difficult, but a similar delay in detection to that in North America would result in a costly and hard to control outbreak. Comparison of degree days between regions suggests that a semivoltine life cycle is most likely in most areas of GB but spread maybe limited by the relatively cool climate in parts of GB. There are several potentially important differences in the biophysical environment in GB compared with North America and European Russia. However, the speed with which it has invaded these areas highlights the need for early surveillance and mitigations to minimise human‐mediated spread of this highly destructive pest.

Captures of Emerald Ash Borer (Agrilus planipennis) Adults in Post-Invasion White Ash Sites with Varying Amounts of Live Phloem

Emerald ash borer (EAB), (Agrilus planipennis Fairmaire), first identified in 2002 in southeast Michigan, has caused catastrophic ash (Fraxinus spp.) mortality in forests within the core of the invasion and has spread to 35 states and five Canadian provinces. Little is known about persistence and densities of EAB populations in post-invasion sites after most ash trees have died. We monitored EAB populations from 2014 to 2016 using double decker (DD) traps set in the midst of white ash (F. americana) trees in 30 post-invasion sites in southeast and south-central Michigan. Two DD traps were deployed at each site. One trap had a dark green upper prism and light purple lower prism, both baited with cis-3-hexenol lures. The other had two dark purple prisms baited with cis-3-hexenol on the upper prism and Manuka oil on the lower prism. In 2014 and 2016, size and condition of ash trees were recorded and area of live white ash phloem was estimated in an 18-m-radius plot centered around each of the DD traps. Area of live white ash phloem per site ranged from approximately 24 to 421 m2 in 2014 and from 24 to 411 m2 in 2016. Canopy condition of live white ash trees generally improved; 65% and 89% of the trees had healthy canopies (&lt;20% dieback) in 2014 and 2016, respectively. Traps in 28, 29 and 30 of the sites captured a total of 580, 585, and 932 EAB adults in 2014–2016, respectively. Area of live ash phloem explained relatively little of the variation in total EAB captures in all three years. Low trap catches, along with relatively stable canopy conditions and continued abundance of live white ash, indicate that EAB populations remain below the carrying capacity of the sites, and ash phloem availability is not a limiting factor for EAB abundance. Further monitoring to track both EAB dynamics and tree condition is needed to determine the long-term outlook for white ash in these sites.

Microbial Control of the Emerald Ash Borer (Coleoptera: Buprestidae) Using Beauveria bassiana (Hypocreales: Cordycipitaceae) by the Means of an Autodissemination Device.

The FraxiProtec, an autodissemination device loaded with the fungus Beauveria bassiana isolate CFL-A, was tested in the field to evaluate its potential to infect emerald ash borer adults and reduce their populations. During the 2-yr experimental period, the dispersion of B. bassiana-infected adults was also documented to assess the dissemination capacity of the biocontrol agent beyond the treated areas. The mean percentage of infected emerald ash borer in 2017 and 2018 in 15 treated sites was 43.3 ± 2.9% and 39.7 ± 3.9%, respectively, and no significant variation was observed over the tested years. Furthermore, a 40% significant reduction of the mean emerald ash borer population growth per tree in treated sites was recorded when compared to the control sites. Emerald ash borer infected with B. bassiana isolate CFL-A were collected from baited sticky traps in the sentinel stations in the area surrounding the FraxiProtec-treated sites. Even at a distance of 125 m, an average of 9.4 ± 2.6% infected emerald ash borer were collected. Finally, exploratory analyzes were carried out on parameters such as the area to be treated, ash tree density, and FraxiProtec density to document potential relationships, which could be used in the determination of a prescription.

Population dynamics of ash across the eastern USA following invasion by emerald ash borer

Non-native insects and pathogens can alter the composition and successional trajectories of forests and, in exceptional cases, drive their host trees functionally extinct. Emerald ash borer has killed millions of ash trees in its invaded range across eastern North America. Predicting the future ecological role of ash requires information on the extent of ash regeneration and recruitment in the wake of invasion. Variable levels of ash regeneration have been observed in stands invaded by emerald ash borer, although recruitment rates of young ash trees into the overstory remain unclear. Here, we used forest inventory data to quantify ash recruitment and regeneration across the eastern United States, and we linked these observed patterns to emerald ash borer invasion history. Inventory data from 2013-2018 indicate there has been extensive ash regeneration in invaded regions, totaling > 1,200 seedlings per ha in counties invaded in 2002–2006. Plots in counties with the longest invasion histories contained the highest densities of ash seedlings and saplings, likely due to the high densities of overstory ash in these areas prior to invasion by emerald ash borer. Seedling densities also remained generally unchanged between inventory periods ending in 2007 and 2018 irrespective of invasion history. Despite this widespread regeneration, ash trees in the smallest overstory class died at faster rates than they were recruited from seedlings or saplings, resulting in negative population trajectories on plots that have been invaded for more than ~ 10 years. This trend suggests that ash will continue to decline in abundance and may become functionally extinct across the invaded range of emerald ash borer. However, the future ecological role of ash will ultimately be determined by the iterative production and survival of ash seeds to reproductive ages in the presence of emerald ash borer populations, along with effective management practices.

Protective neighboring effect from ash trees treated with systemic insecticide against emerald ash borer.

BACKGROUNDThe emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) is now the most destructive invasive species in North America. While biocontrol using parasitoids shows promising results in natural forests, strategies are needed to protect high‐value trees against invasive EAB populations. Emamectin benzoate is a commonly used systemic insecticide for the protection of valuable trees. Methods that optimize its use allow for reduced quantities of insecticide to be released in the environment and save time and money in efforts to protect ash trees from EAB. We hypothesize that a treated tree can also offer a protective neighboring effect to nearby untreated ash trees, allowing for an optimized spatial planning of insecticide applications.RESULTSWe sampled 896 untreated ash trees, in the vicinity of treated trees, in Maryland and Washington DC. We recorded signs of EAB infestation (canopy condition, exit holes, wood pecks, epicormic growth, and bark splits). Two subsequent yearly samplings were made of 198 and 216 trees, respectively. We also present a novel proximity index for this particular application. Results show consistent decrease in EAB infestation signs in untreated trees as proximity to treated trees increases.CONCLUSIONResults support that a neighboring effect occurs. However, proximity to treated trees must be high for a tree to be safely left untreated. This proximity seems rare in forests, but can happen in urban/planted landscapes. Future studies should test and validate these findings, and could lead to a more precise recommended safe index tailored across multiple ash species and geographic regions.

Gut microbiome of the emerald ash borer, Agrilus planipennis Fairmaire, and its relationship with insect population density.

The gut microbial communities of beetles play crucial roles in their adaptive capacities. Environmental factors such as temperature or nutrition naturally affect the insect microbiome, but a shift in local conditions like the population density on a host tree could also lead to changes in the microbiota. The emerald ash borer (EAB), Agrilus planipennis Fairmaire, is an exotic wood borer that causes environmental and economic damage to ash trees in North America. This study aimed to describe the taxonomic structure of the EAB gut microbiome and explore its potential relationship with borer population size. The number of EAB adults collected per tree through a 75km transect from an epicenter allowed the creation of distinct classes of population density. The Gammaproteobacteria and Ascomycota predominated in bacterial and fungal communities respectively, as determined by sequencing of the bacterial 16S rRNA gene and the fungal internal transcribed spacer ITS2. Species richness and diversity of the bacterial community showed significant dependence on population density. Moreover, α-diversity and β-diversity analysis revealed some indicator amplicon sequence variants suggesting that the plasticity of the gut microbiome could be related to the EAB population density in host trees.

Horizontal Transmission of the Entomopathogenic Fungal Isolate INRS-242 of Beauveria bassiana (Hypocreales: Cordycipitaceae) in Emerald Ash Borer, Agrilus planipennis (Coleoptera: Buprestidae).

Emerald ash borer (EAB), Agrilus planipennis Fairmaire, is an invasive and destructive beetle that causes extensive damage to ash trees in North America. The entomopathogenic fungus Beauveria bassiana Vuillemin is considered as an effective biological control agent for EAB adult populations. Using an autodissemination device with a fungal isolate of B. bassiana, our research aims to investigate the possibility of horizontal transmission of the fungal disease from infected to uninfected EAB adults during mating. Results show that the efficiency of fungal transmission is significantly related to the sex of EAB carrying the fungal pathogen. EAB males are the promising vector to transmit mycosis to their partners during mating. Results strengthen the potential of the fungal autodissemination device as a powerful biological strategy to control EAB populations.

Modeling Agrilus planipennis F. (Coleoptera: Buprestidae) Spread in New Jersey

Pests and disease have become an increasingly common issue as globalized trade brings non-native species into unfamiliar systems. Emerald ash borer (Agrilus planipennis), is an Asiatic species of boring beetle currently devastating the native population of ash (Fraxinus) trees in the northern forests of the United States, with 85 million trees having already succumbed across much of the Midwest. We have developed a reaction-diffusion partial differential equation model to predict the spread of emerald ash borer over a heterogeneous 2-D landscape, with the initial ash tree distribution given by data from the Forest Inventory and Analysis. As expected, the model predictions show that emerald ash borer consumes ash which causes the local ash population to decline, while emerald ash borer spreads outward to other areas. Once the local ash population begins to decline emerald ash borer also declines due to the loss of available habitat. Our model's strength lies with its focus on the county scale and its linkage between emerald ash borer population growth and ash density. This enables one to make accurate predictions regarding emerald ash borer spread which allows one to consider various methods of control as well as to accurately study the economic effects of emerald ash borer spread.

Host range expansion may provide enemy free space for the highly invasive emerald ash borer

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an aggressive invader from Asia that has killed millions of trees in North America, causing substantial ecosystem effects and economic losses. All North American ash, Fraxinus spp., are thought to be susceptible, but recently emerald ash borer has been documented developing in a novel host, white fringetree, Chionanthus virginicus. We evaluated larval performance in two common ash species and white fringetree by infesting bolts with emerald ash borer eggs. In addition we evaluated cambial nitrogen, carbon, carbon:nitrogen, stem density, and response to artificial wounding, to determine which host plant characteristics most influence larval development. We also conducted choice and no choice assays using the classical biological control agent, Tetrastichus planipennisi Yang (Hymenoptera: Eulophidae), to assess its ability to locate larval emerald ash borer in the different host plants. We found significantly lower survival rates of emerald ash borer larvae in white fringetree compared to white ash, F. americana. Larval phloem consumption and larval growth were lower in fringetree than in either white or blue ash, F. quadrangulata. Carbon content and density were greater in fringetree than in either ash species. Response to wounding, measured by callus tissue formation, was greatest in white ash. In choice assays, T. planipennisi only parasitized emerald ash borer larvae in ash bolts, and in no-choice tests failed to parasitize larvae in fringetree. Our findings corroborate studies showing that fringetree is a suitable host for emerald ash borer larvae. Failure of T. planipennisi to parasitize larvae within fringetree has implications for the efficacy of this classical biological control agent in regulating emerald ash borer populations. Coupled with the use of white fringetree as a reservoir host, the enemy free space provided to emerald ash borer through use of this alternate host may have significant repercussions for emerald ash borer invasion dynamics.

Dispersal of emerald ash borer (Coleoptera: Buprestidae) parasitoids along an ash corridor in western New York

Previous studies have documented that parasitoids introduced to North America for biological control of emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), are establishing and persisting. However, no study has explicitly assessed their dispersal capabilities. In 2013 and 2014, we released Spathius agrili Yang (Hymenoptera: Braconidae), Tetrastichus planipennisi Yang (Eulophidae), and Oobius agrili Zhang and Huang (Encyrtidae) at 5 km intervals along 20 km of an ash (Fraxinus spp.) corridor, along which EAB was spreading. From 2013 to 2017, we deployed yellow pan traps every 250 m to detect parasitoid dispersal along the corridor; traps were checked weekly throughout the summer. In 2014, 2015, and 2016, ash health data were collected at each trap location. In 2016, additional traps were established parallel to the study area to detect dispersal away from the corridor. EAB were recovered in traps each year of the study and severity of ash decline aligned with EAB trap detections to indicate build-up and movement of EAB populations. Tetrastichus planipennisi were first recovered in 2014 and trap recoveries increased each subsequent year of the study. The other parasitoid species were not recovered. In 2016, T. planipennisi were detected ∼10 km from release points, established in areas with high EAB population densities, and were detected in traps ∼3.9 km away from the corridor. By 2017, T. planipennisi were recovered along the entire study area. This study quantifies dispersal of T. planipennisi and suggests it will be an important biological control agent of EAB in North America.

Ecological Impacts of Emerald Ash Borer in Forests at the Epicenter of the Invasion in North America

We review research on ecological impacts of emerald ash borer (EAB)-induced ash mortality in the Upper Huron River watershed in southeast Michigan near the epicenter of the invasion of North America, where forests have been impacted longer than any others in North America. By 2009, mortality of green, white, and black ash exceeded 99%, and ash seed production and regeneration had ceased. This left an orphaned cohort of saplings too small to be infested, the fate of which may depend on the ability of natural enemies to regulate EAB populations at low densities. There was no relationship between patterns of ash mortality and ash density, ash importance, or community composition. Most trees died over a five-year period, resulting in relatively simultaneous, widespread gap formation. Disturbance resulting from gap formation and accumulation of coarse woody debris caused by ash mortality had cascading impacts on forest communities, including successional trajectories, growth of non-native invasive plants, soil dwelling and herbivorous arthropod communities, and bird foraging behavior, abundance, and community composition. These and other impacts on forest ecosystems are likely to be experienced elsewhere as EAB continues to spread.

Interactions between woodpecker attack and parasitism by introduced parasitoids of the emerald ash borer

Agrilus planipennis, the emerald ash borer (EAB), is an invasive forest pest causing significant economic and ecological impacts. EAB is attacked by some native natural enemies, the most significant being woodpeckers, which can remove between 30 and 95% of the EAB larvae in a tree. However, despite high woodpecker predation rates, EAB populations continue to grow. Management of EAB focuses on classical biological control, with the introduction of four parasitic wasps from Asia. Because both woodpeckers and larval parasitoids attack mature EAB larvae, their impacts overlap and potentially interact. This study examines the relationship between native woodpecker predation and parasitism by the introduced parasitoids S. agrili and T. planipennisi. We established a cohort of parasitized larvae on select ash trees and then used screening to exclude woodpeckers from some sections of the tree. We show that while woodpeckers had no effect on observed parasitism rates of individual trees, the presence of parasitized larvae changed woodpecker foraging behavior and resulted in significantly lower overall foraging by woodpeckers. We hypothesize these changes are due to these larval parasitoids being a lower quality food reward. Parasitism of EAB larvae could contribute to a decrease in patch quality for woodpeckers such that they would quit foraging sooner than expected if it were a high-quality, un-parasitized patch. This study fills a gap in our understanding of the complex relationship between woodpecker mortality and parasitism mortality of EAB and our results demonstrate that this relationship may have broad implications for the EAB biological control program.

Density of Emerald Ash Borer (Coleoptera: Buprestidae) Adults and Larvae at Three Stages of the Invasion Wave.

Emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae), an invasive phloem-feeding buprestid, has killed hundreds of millions of ash (Fraxinus spp.) trees in the United States and two Canadian provinces. We evaluated EAB persistence in post-invasion sites and compared EAB adult captures and larval densities in 24 forested sites across an east-west gradient in southern Michigan representing the Core (post-invasion), Crest (high EAB populations), and Cusp (recently infested areas) of the EAB invasion wave. Condition of green ash (Fraxinus pennsylvanica Marsh) trees were recorded in fixed radius plots and linear transects in each site. Ash mortality was highest in Core sites in the southeast, moderate in Crest sites in central southern Michigan, and low in Cusp sites in the southwest. Traps and trap trees in Crest sites accounted for 75 and 60% of all EAB beetles captured in 2010 and 2011, respectively. Populations of EAB were present in all Core sites and traps in these sites captured 13% of all beetles each year. Beetle captures and larval densities at Cusp sites roughly doubled between 2010 and 2011, reflecting the increasing EAB populations. Sticky bands on girdled trees captured the highest density of EAB beetles per m2 of area, while baited double-decker traps had the highest detection rates and captured the most beetles. Larval densities were higher on girdled ash than on similar ungirdled trees and small planted trees. Woodpecker predation and a native larval parasitoid were present in all three invasion regions but had minor effects on ash survival and EAB densities.

Optimizing Use of Girdled Ash Trees for Management of Low-Density Emerald Ash Borer (Coleoptera: Buprestidae) Populations.

Effective survey methods to detect and monitor recently established, low-density infestations of emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), remain a high priority because they provide land managers and property owners with time to implement tactics to slow emerald ash borer population growth and the progression of ash mortality. We evaluated options for using girdled ash (Fraxinus spp.) trees for emerald ash borer detection and management in a low-density infestation in a forested area with abundant green ash (F. pennsylvanica). Across replicated 4-ha plots, we compared detection efficiency of 4 versus 16 evenly distributed girdled ash trees and between clusters of 3 versus 12 girdled trees. We also examined within-tree larval distribution in 208 girdled and nongirdled trees and assessed adult emerald ash borer emergence from detection trees felled 11 mo after girdling and left on site. Overall, current-year larvae were present in 85-97% of girdled trees and 57-72% of nongirdled trees, and larval density was 2-5 times greater on girdled than nongirdled trees. Low-density emerald ash borer infestations were readily detected with four girdled trees per 4-ha, and 3-tree clusters were as effective as 12-tree clusters. Larval densities were greatest 0.5 ± 0.4 m below the base of the canopy in girdled trees and 1.3 ± 0.7 m above the canopy base in nongirdled trees. Relatively few adult emerald ash borer emerged from trees felled 11 mo after girdling and left on site through the following summer, suggesting removal or destruction of girdled ash trees may be unnecessary. This could potentially reduce survey costs, particularly in forested areas with poor accessibility.