Invasive Emerald Ash Borer Research Articles

Distinct metabolites affect the phloem fungal communities in ash trees (Fraxinus spp.) native and nonnative to the highly invasive emerald ash borer (AGRILUS PLANIPENNIS).

Emerald ash borer (EAB, Agrilus planipennis) is an invasive killer of ash trees (Fraxinus spp.) in North America and Europe. Ash species co-evolved with EAB in their native range in Asia are mostly resistant, although the precise mechanism(s) remain unclear. Very little is also known about EAB or ash tree microbiomes. We performed the first joint comparison of phloem mycobiome and metabolites between a native and a nonnative ash species, infested and uninfested with EAB, in conjunction with investigation of larval mycobiome. Phloem mycobiome communities differed between the tree species, but both were unaffected by EAB infestation. Several indicator taxa in the larval gut shared a similarly high relative abundance only with the native host trees. Widely targeted metabolomics revealed 24 distinct metabolites in native trees and 53 metabolites in nonnative trees, respectively, that differed in relative content between infested and uninfested trees only in one species. Interestingly, four metabolites shared a strong relationship with the phloem mycobiomes, majority of which affected only the native trees. Collectively, our results demonstrate a complex interplay between host tree chemistry and mycobiome, and suggest the shared relationships between the mycobiomes of the native host tree and EAB may reflect their shared co-evolution.

Detection of emerald ash borer damage using an improved change detection method: Integrating host phenology and pest life history

Invasive Emerald Ash Borer (EAB) damage pose significant challenges for sustainable forest management, necessitating accurate mapping of damaged ash trees. Traditional change detection methods, using time-series imagery, are essential for monitoring forest disturbances but complicated by abnormal fluctuations in original time-series features. Tree phenology also complicates this process by masking the reflectance characteristics indicative of EAB infestation. To address these challenges, we propose an improved change detection method integrating patterns from host tree phenology and EAB life history. This improved method includes: (1) select the indices with time stability to enhance detection reliability by partial least squares method (PLS); (2) correction on negative change values before and positive change values after the phenological peak based on known patterns of tree phenology and EAB life history. Result confirms that this method effectively reflects the seasonal growth and decline dynamics of ash trees, revealing the impacts of phenology and EAB infestation. EAB-damaged trees exhibited slower growth in May and premature decline in July compared with healthy tree, with the damage severity influencing the rate of leaf decline. This proposed method achieved an overall accuracy of 53.4%-76.7% across different months for ash trees with health, light and severe damage. This study highlights the capabilities of integrating pest life history and phenology in change detection method and provide a new method to monitor individual tree health across large areas by high-resolution satellite imagery.

Observations of reduced ET and persistent elevated water table beneath a riparian forest gap following emerald ash borer invasion and tree mortality

AbstractEmerald ash borer (EAB) (Agrilus planipennis Fairmaire), an invasive, phloem‐feeding beetle native to Asia, has killed millions of ash (Fraxinus spp.) trees in North America since it was detected in southeast Michigan in 2002. Consistently high mortality of black ash (Fraxinus nigra) and green ash (F. pennsylvanica) which often occur in riparian forests is a concern given their role in regulating soil moisture and shallow groundwater levels. We monitored and compared hydrologic processes in a riparian forest impacted by EAB invasion and an adjacent unimpacted riparian forest site in southwest Michigan. From 2018 to 2022, we recorded soil moisture, depth to groundwater and meteorological variables at 15‐min intervals throughout the growing season in a canopy gap following EAB‐caused ash mortality and in adjacent, unaffected forest in the Augusta Creek riparian zone. Groundwater contributions to evapotranspiration (ETG) were estimated using a groundwater level fluctuation (WLF) method. Significant differences in volumetric soil moisture content (16%–26% higher in the gap than forest), average depth to water (10 cm in the gap vs. 70 cm below land surface in the forest) and mean daily ETG (0.6 in the gap vs. 3.0 mm per day in the forest) persisted across four growing seasons. Within the gap, prolonged saturation of the near surface may be contributing to a shift from a forested riparian ecosystem to herb and sedge‐dominated wetland. These differences have implications for an array of riparian zone ecosystem services, a concern given the extent of ash mortality already sustained in much of eastern North America.

Spread management priorities to limit emerald ash borer (Agrilus planipennis) impacts on United States street trees

AbstractThe invasive emerald ash borer (Agrilus planipennis) causes damage to street trees which is estimated to reach US$ 900 million over the next 30 years. Although millions of dollars are spent annually to control this species, spatiotemporal management plans are often based on rules of thumb that ignore future pest dispersal. Here, we reveal an optimal management strategy to protect urban trees in North America from A. planipennis. To achieve this, we embedded a pest dispersal model within a mixed integer programming framework. We discovered that optimized strategies consistently outperformed those based on rules of thumb, potentially resulting in the protection of an additional nearly 1 million street trees and savings of $ 629 million. Critically, the best management strategies always relied on quarantines and biological control (constituting 98–99% and 1–2% of the project budget, respectively), in contrast with current practices, where federal spending has been diverted to biological control. Our findings serve to inform future pest control efforts and can help protect many more trees from this invasive species.

The lichen genus <i>Rinodina</i> (Physciaceae) in New Brunswick, Canada

Fifteen species of the crustose lichen genus Rinodina are confirmed in New Brunswick, Canada. We report four corticolous species, Rinodina pachysperma, Rinodina populicola, Rinodina septentrionalis, and Rinodina tenuis, and the saxicolous Rinodina tephraspis in the province for the first time. A previous report of Rinodina granuligera is based on a specimen that we have re-identified as Rinodina cinereovirens. We note distinguishing characteristics, habitats, substrata, relative abundance, and biogeographic relationships of each species and provide an identification key and distribution maps. The most frequently occupied phorophytes (tree substrata) are Sugar Maple (Acer saccharum), Yellow Birch (Betula alleghaniensis), and Eastern White Cedar (Thuja occidentalis). Some species are closely associated with particular habitats, phorophytes, or both. For example, we found R. pachysperma only in floodplain forests dominated by Silver Maple (Acer saccharinum), and R. tenuis only on Eastern White Cedar in wet cedar-dominated stands. In contrast, we recorded Rinodina freyi on numerous phorophyte species in a relatively wide range of habitats. Other than Eastern White Cedar and Balsam Fir (Abies balsamea), conifers are rarely colonized by Rinodina species in New Brunswick. Most Rinodina species are probably not currently of conservation concern in the province. However, R. cinereovirens is known from only two collections, one dating from 1902. The other, from 2007, was on Black Ash (Fraxinus nigra) in a swamp forest next to an active peat-mining operation. The expected devastation of ash species by the invasive Emerald Ash-borer (Agrilus planipennis) is a further threat to this occurrence and to any lichens for which ash may be an important phorophyte.

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.

Emerald ash borer (Agrilus planipennis) infestation bioassays and metabolic profiles of green ash (Fraxinus pennsylvanica) provide evidence for an induced host defensive response to larval infestation

IntroductionLarvae of the invasive emerald ash borer [EAB, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)], kill over 99% of green ash (Fraxinus pennsylvanica Marshall) trees they infest, yet a small percentage of green ash (“lingering ash”) survive years of heavy EAB attack. In the face of an ongoing invasion that threatens multiple North American Fraxinus species with extinction, any evidence for reproducible defensive responses in the native species merits investigation.MethodsWe evaluated the capacity of three families of green ash F1 progeny to kill EAB larvae when challenged in greenhouse studies by infestation with a uniform density of EAB eggs followed by dissection 8 weeks post-infestation and comparison of the host metabolomic profiles.ResultsThe mean proportions of host-killed larvae in the two families of F1 progeny from lingering ash parents were significantly higher than that of host-killed larvae in the family of F1 progeny from susceptible ash parents (p &amp;lt; 0.001). Untargeted metabolomics comparing F1 progeny in the quartile with the highest percent host-killed larvae (HHK) to F1 progeny in the quartile with the lowest percent host-killed larvae (LHK) and to the uninfested F1 progeny within each family revealed evidence for induced biochemical responses to EAB. Infested trees produced significantly higher levels of select secoiridoids than uninfested trees, and LHK progeny produced significantly higher levels of select secoiridoids than the HHK progeny. HHK progeny produced significantly higher abundances of three metabolites annotated as aromatic alkaloids than the LHK and uninfested individuals.DiscussionBased on these results, we hypothesize that green ash responds to EAB infestation. However, only certain trees have the genetic capacity to tailor a response that kills enough EAB larvae to prevent lethal damage to the vascular system. Rigorous tests of this hypothesis will require 15–20 years of additional crossing, phenotyping, and omics analyses. The results of this investigation will encourage the establishment and continuation of breeding programs that, in concert with biocontrol and management, could provide trees that slow, if not halt, the decimation of the Fraxinus gene pool. At the same time, ongoing work on host-insect interaction will contribute to our understanding of how forest trees recognize and defend themselves against phloem-feeding insects.

Towards Tree Species Preservation: Protecting Ash Amidst the Emerald Ash Borer Invasion in the Northeast

Abstract The introduced emerald ash borer (EAB) represents the costliest invasive forest insect in US history, causing significant mortality of ash species across much of eastern North America as well as in Colorado and Oregon. Few surviving overstory ash trees exist in areas first invaded by EAB, such as the Lake States region; however, forests with healthy, mature ash remain in recently invaded regions, such as the northeastern United States. Given the importance of ash to cultural lifeways of Indigenous peoples and the ecology and economies of working forest lands, there is growing interest in applying protection measures to maintain ash in forested settings. We further develop our call for species preservation by presenting Indigenous and Western science case studies of ongoing efforts to mitigate the impacts of EAB, illustrating specific applications of these strategies for meeting different preservation goals in lowland and northern hardwood forests in northeastern North America. Study Implications: The introduced emerald ash borer (EAB) threatens to functionally eliminate ash species from large portions of the United States. Although the impacts of EAB are now widespread in many areas, portions of the United States, such as the Northeast, still contain forests with healthy, mature ash. This presents a unique opportunity to apply the integrated pest management strategies and knowledge gained from other invaded regions to preserve the cultural and ecological values provided by ash in the forest. Multistakeholder partnerships built around preserving the cultural and ecological values of ash have provided a powerful approach for sustaining ash into the future.

Biological invasion threatens keystone species indelibly entwined with Indigenous cultures

Black ash (Fraxinus nigra), the most highly preferred and vulnerable host of the invasive emerald ash borer (EAB; Agrilus planipennis) in North America, is of cultural and spiritual importance to many Tribal Nations in the US and First Nations in Canada. To date, EAB has invaded nearly 60% of the native range of black ash, with annual spread averaging approximately 50 km per year. On the basis of the predicted expansion of EAB distribution, we estimate that more than 75% of black ash basal area will be lost across 87% of the species’ North American range by 2035. Census data indicate that 98% of Indigenous people currently residing within the geographic range of black ash in the US will be within the area experiencing more than 75% basal area loss by 2035, suggesting broad and multidimensional impacts of EAB invasion for those who value black ash as a cultural keystone species. Collaborative efforts among scientists, resource managers, and Indigenous experts are needed to mitigate EAB impacts and preserve or protect black ash resources, given the species’ vulnerability to EAB and its associated cultural and ecological value.

Forester and Logger Response to Emerald Ash Borer in Massachusetts and Vermont: A Secondary Disturbance

Abstract Forester and logger responses to the invasive emerald ash borer (EAB) could substantially affect regions across the United States. We analyzed forester and logger responses to EAB in Massachusetts and Vermont, exploring characteristics associated with purposeful targeting of substantial ash properties; managing forests differently because of EAB; and regeneration goals. One-third of respondents increased timber sales on ash properties, motivated by ecological, not economic, impacts of EAB. Nearly 60% said EAB changed their management activity in stands with ash; changes influenced by the ecological impact of EAB and not economic factors. Those influenced by EAB’s ecological impact to choose properties with substantial ash were more likely to have increased harvest area size, sawtimber removal, and harvest intensity. Loggers were more likely than foresters to remove small-diameter ash and low-grade trees. Both rated regenerating economically valuable species well adapted to the site as their highest essential priority.

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.

Potential Westward Spread of Emerald Ash Borer, Agrilus planipennis Fairmaire, 1888 (Coleoptera: Buprestidae) from Eastern Ukraine

Emerald ash borer (EAB), Agrilus planipennis, is a phloem-boring beetle, native to East Asia that has become a serious invasive pest of ash (Fraxinus spp.) trees in North America and European Russia since the early 2000s. In 2019, EAB was detected in Ukraine. It had spread over 300 km from the entry point over two years and killed hundreds of Fraxinus excelsior and F. pennsylvanica trees. EAB poses a threat to the ash forests of neighboring European countries, which have already been damaged by the invasive fungus Hymenoscyphus fraxineus. The purpose of this research was (i) to reveal the traits of EAB and the climatic variables that affect its survival; (ii) to predict the EAB expansion range in Ukraine and westward; and (iii) to compare the most significant bioclimatic variables in the native, invasive ranges of EAB, as well as outside these ranges. The results demonstrated the following: (i) in all ranges, EAB has adapted to the seasonal temperature variations; (ii) the MaxEnt model predicted the potential distribution of EAB with high accuracy (AUC = 0.988); the predicted area of EAB invasion covered 87%, 48%, and 32% in Luhansk, Kharkiv, and Donetsk regions, respectively; and (iii) the ranges of climatic variables in EAB-inhabited regions demonstrated the high ecological plasticity of this pest. However, the predictions could be improved by considering forest structure, as well as the localization of roads.

Can invasive species lead to sedentary behavior? The time use and obesity impacts of a forest-attacking pest

Invasive species can significantly disrupt environmental quality and flows of ecosystem services and we are still learning about their multidimensional impacts to economic outcomes of interest. In this work, I use quasi-random US county detections of the invasive emerald ash borer (EAB), a forest-attacking pest, to investigate how invasive-induced deforestation can impact obesity rates and time spent on physical activity. Results suggest that EAB is associated with 1–4 percentage points (pp) (mean = 37.0%) annual losses of deciduous forest cover in infested counties. After EAB detection, obesity rates are higher by 2.5pp (mean = 24.7%) and daily minutes spent on physical activity are lower by 4.9 minutes (mean = 51.7 min), on average. I show that less time spent on outdoor sports and exercise is one possible, but not exclusive, mechanism. Nationwide, EAB is associated with $3.0 billion in annual obesity-related healthcare costs over 2002–2012, equivalent to approximately 1.2% of total annual US medical costs related to obesity. Results are supported by many robustness and falsification tests and an alternative IV specification. This work has policy implications for invasive species management and expands our understanding of invasive species impacts on additional economic outcomes of interest.

Specialist Herbivore Performance on Introduced Plants During Native Host Decline.

Ash (Fraxinus spp.) is in rapid decline across the northeastern USA due to the invasive emerald ash borer (Agrilus planipennis Fairmaire). Three recently co-occurring confamilial species may serve as alternative larval host plants for ash-reliant Lepidoptera. These prospective hosts are nonnative shrubs often planted in managed suburban landscapes and are sometimes invasive or naturalized in North America. Given the imminent decline of ash trees, we considered potential downstream effects on insect herbivores historically specialized on ash foliage. We measured the performance of three ash-specialist hawkmoths (Lepidoptera: Sphingidae) on native white ash (Fraxinus americana L.) and alternative host plants: common lilac (Syringa vulgaris L.), weeping forsythia [Forsythia suspensa (Thunb.) Vahl], and European privet (Ligustrum vulgare L.). We found the nonnative host plants provided varied support for larval survival to pupation, with biomass and growth rate affected differently by both plant and insect identity. Nearly all caterpillars reared on one alternative host, European privet, exhibited distinct malformations of the wing buds at pupation. Given caterpillar presence on privet in the field, privet may constitute an ecological trap (i.e., when female moths select a sub-optimal host, offspring survival and fitness are reduced). This work demonstrates how performance testing can reveal species-specific effects of host plant loss on mono- or oligophagous insects. For some ash specialists, alternative nonnative host plants may be suboptimal, but some cultivated host plants may be able to support certain specialist insects during native host decline. We suggest that landscaping decisions can be tailored to support threatened insect species.

Effects of flood duration on seedling survival and growth of potential replacement species in black ash (Fraxinus nigra Marshall) forests threatened by emerald ash borer

Within black ash (Fraxinus nigra Marshall) wetlands, black ash acts as a foundational species, resulting in high vulnerability to the invasive emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae). One mitigation strategy being considered is the planting of alternative tree species to increase compositional diversity, however, there is limited understanding of how replacement tree species tolerate flooding. A greenhouse experiment was used to explore early survival and growth of eighteen tree species in response to five flooding durations (3, 6, 9, 12, or 15 weeks). Seedlings were assigned to flood tolerance groups according to their responses to the various flooding duration treatments. Taxodium distichum (L.) Rich., Ulmus americana L., and Betula nigra L. were able to survive and grow with flooding durations of up to 15 weeks. Thuja occidentalis L., Acer rubrum L., Larix laricina (Du Roi) K. Koch, Quercus bicolor Willd., and Betula alleghaniensis Britton had high survival and growth rates with flooding durations up to 6 weeks in length. Finally, Juglans nigra L. and Acer saccharum Marshall responded poorly to flooding of any duration. These results can assist managers in matching potential black ash replacement species to the hydrology of their local black ash wetlands.

Emerald ash borer invasion of riparian forests alters organic matter and bacterial subsidies to south Michigan headwater streams.

Emerald ash borer (EAB) has killed millions of ash trees in the United States and Canada, yet impacts on terrestrial-aquatic linkages are largely unknown. Ash tree death along streams creates canopy gaps, increasing light to riparian plants and potentially affecting organic matter subsidies. Six EAB-related canopy gaps along streams across a gradient of timing of EAB invasion in Michigan were characterized for coarse woody material (CWM), terrestrial and aquatic leaf litter and their associated bacterial communities, and macroinvertebrates upstream, downstream, and at the center of the gap. Stream sites downstream of EAB-related canopy gaps had significantly lower dissolved oxygen and macroinvertebrate diversity than sites upstream and at the gaps. Yet there was no difference in CWM or aquatic leaf litter, likely due to downstream movement of organic matter from upstream riparian sources. Low abundance bacterial amplicon sequence variants unique to gap or forest were detected in leaves and leaf litter, suggesting that EAB-related canopy gaps altered leaf-associated bacterial communities. Overall, EAB invasion indirectly impacted some variables, while organic matter dynamics were resistant to change.

Predicting Emerald Ash Borer Adult Emergence and Peak Flight Activity in Winnipeg, Manitoba, Canada

The invasive emerald ash borer (Agrilus planipennis Fairmaire; Coleoptera: Buprestidae) has killed tens of millions of ash (Fraxinus spp.) trees across North America. A. planipennis was first detected in Winnipeg, Manitoba in 2017 and has the potential to become a serious threat to the city's ash canopy which accounts for ~30% of the public tree inventory. The goal of this study was to predict when adult A. planipennis emergence and peak activity would occur in Winnipeg to help logistical planning for the implementation of a city-wide management program. The management program would focus on detection and limiting the spread of the beetle with the objective of preserving ash trees as long as possible allowing for more proactive management of the EAB infestation. To predict adult emergence and peak activity of A. planipennis, we used local weather station data to calculate the number of degree-days accumulated in each year for the 1970–2019 period using three different degree-day accumulation models. Developmental thresholds for A. planipennis were derived from previous North American studies. The estimated mean emergence dates for the 50-year period were June 14 ± 8.5 days (double sine model), June 14 ± 8.5 days (single sine model), and June 19 ± 9.1 days (standard model) whereas the peak activity dates were July 16 ± 8.8 days (double sine model), July 17 ± 8.7 days (single sine model), and July 21 ± 9.4 days (standard model). Meteorological records indicate that temperatures in the Winnipeg region have increased over the study period. However, our predicted emergence dates do not significantly differ over the 50 years examined in the study, although estimated peak activity dates are significantly earlier, suggesting that EAB movement may benefit from climate change. The results from this study will provide managers with information regarding the temporal behavior of A. plannipennis in Winnipeg allowing for improved timing of control measures and monitoring, thereby extending the projected life span of a significant ash tree population within the Winnipeg urban region. The management model developed for Winnipeg could serve as an example for other locations in the prairie region of North America.

Stand dynamics and structure of old-growth Fraxinus nigra stands in northern Minnesota, USA

Black ash ( Fraxinus nigra Marsh.) forests of north-central North America are currently threatened by the non-native emerald ash borer ( Agrilus planipennis, EAB). Despite the wide distribution of F. nigra ecosystems, and the concern over EAB impact, little is known about their structure and natural stand dynamics. We sampled six old-growth F. nigra stands to assess structure, composition, tree recruitment, and past disturbance. Dendrochronological results revealed that disturbance rates fluctuated markedly over the past 200 years or more, but remained relatively low, suggesting small- to moderate-scale disturbances. Recruitment age structures revealed that ( i) F. nigra is able to maintain long-term dominance through extended longevity as a canopy tree, and ( ii) these systems have fairly continuous recruitment over time, with most sites showing F. nigra recruitment in every decade in the chronology. We speculate that recruitment is coupled with water table fluctuations, in addition to canopy disturbance, as these stands are subject to both frequent flooding and effective soil drought (given the shallow root systems). The low rates of past canopy disturbance and associated gap-phase replacement by F. nigra highlight the potential for dramatic shifts in these systems following emerald ash borer invasion and subsequent canopy tree mortality.

Invasion of Emerald Ash Borer Agrilus planipennis and Ash Dieback Pathogen Hymenoscyphus fraxineus in Ukraine—A Concerted Action

Emerald Ash Borer (EAB), Agrilus planipennis, is a beetle that originates from East Asia. Upon invasion to North America in the early 2000s, it killed untold millions of ash trees. In European Russia, EAB was first detected in Moscow in 2003 and proved to have the potential to also kill native European ash (Fraxinus excelsior). The beetle has since spread in all geographic directions, establishing itself in eastern Ukraine by 2019 and possessing potential for further westward spread towards the EU. Apart from the approaching EAB, F. excelsior is currently threatened by the dieback disease (ADB) caused by the invasive ascomycete fungus Hymenoscyphus fraxineus. The infestation by EAB combined with ADB infection is expected to be more lethal than either of them alone, yet the potential consequences are unknown. To date, eastern Ukraine represents the geographic area in which both invasions overlap, thus providing the opportunity for related investigations. The aims of the study were to investigate: (i) the EAB expansion range in Ukraine, (ii) the relative susceptibility of F. excelsior and American ash (Fraxinus pennsylvanica) to EAB and ADB, and (iii) the combined effect/impact on ash condition imposed by both the pest and disease in the area subjected to the invasion. The results have demonstrated that (i) the invasion of EAB is currently expanding both in terms of newly infested trees and invaded geographic area; (ii) F. excelsior is more resistant to EAB than F. pennsylvanica, while F. excelsior is more susceptible to ADB than F. pennsylvanica; and (iii) the infection by ADB is likely to predispose F. excelsior to the infestation by EAB. It was concluded that inventory and mapping of surviving F. excelsior, affected by both ADB and EAB, is necessary to acquire genetic resources for the work on strategic, long-term restoration of F. excelsior in devastated areas, thereby tackling a possible invasion of EAB to the EU.

The value of hybrid and non‐native ash for the conservation of ash specialists is limited following late stages of emerald ash borer invasion

Abstract Widespread mortality of native North American ash caused by emerald ash borer (EAB; Agrilus planipennis Fairmaire) threatens native arthropod biodiversity, but hybrid ash populations with resistance to EAB may serve a role in supporting threatened communities of arthropods in managed landscapes impacted by EAB. In this study, we investigated the hypothesis that a North American × Asian hybrid ash could serve as a refuge for North American arthropods in a common garden experiment by comparing beetle communities and herbivory on North American green and black ash, the Asian Manchurian ash, and the black × Manchurian hybrid ‘Northern Treasure’ ash. We found that ash specialists were rare among trees in the common garden. Species richness and composition of herbivorous beetles, as well as levels of herbivory, were similar among ash taxa, and these patterns were driven by native generalists. The lack of ash specialists collected suggests that regions that have experienced late stages of EAB‐induced ash mortality may have missed the opportunity to conserve populations of native specialist herbivores with EAB‐resistant ash genotypes. To maximize the potential for conserving native arthropod biodiversity of ash, it may be necessary to plant resistant ash prior to widespread EAB‐induced ash mortality, prioritizing efforts on the leading edge of expanding distribution of EAB.