Ash survival and growth response to emerald ash borer invasion in Massachusetts riparian forests: impacts of biological control

Authors: GREEN, MITCHELL - University Of Massachusetts; Duan, Jian; CRANDALL, RYAN - University Of Massachusetts; VAN DREISCHE, ROY - University Of Massachusetts; MARTINEZ, ARMAND - University Of Massachusetts; ANDERSEN, JEREMY - University Of Massachusetts; ELKINTON, JOSEPH - University Of Massachusetts

Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2025
Publication Date: 6/28/2025
Citation: Green, M.A., Duan, J.J., Crandall, R.S., Van Dreische, R.G., Martinez, A., Andersen, J.C., Elkinton, J.S. 2025. Ash survival and growth response to emerald ash borer invasion in Massachusetts riparian forests: impacts of biological control. Forest Ecology and Management. https://doi.org/10.1016/j.foreco.2025.122951.
DOI: https://doi.org/10.1016/j.foreco.2025.122951

Interpretive Summary: The emerald ash borer (EAB) is a serious invasive pest that has killed hundreds of millions of North American ash (Fraxinus) trees. Loss of ash species due to EAB has widespread implications for our forest ecosystems. Biological control through the introduction of natural enemies (parasitic wasps) from EAB’s native range in northeast Asia is a potential long-term management solution, however it is not known if this approach can protect mature (canopy) ash trees that are often quickly killed by the initial wave of EAB invasion. In the present study, we evaluate the ash growth and survival response to EAB invasion at six floodplain forests in Massachusetts and impact of early releases of biological control agents (Oobius agrili, Spathius galinae, and Tetrastichus planipennisi) on ash survival. We detected parasitism (attack) of EAB by all three released biocontrol agents in all three release sites and two of the non-release sites and found that the level of attack on EAB larvae by the released biocontrol agents negatively correlated with ash mortality rates across our study sites, indicating that these biocontrol agents might have contributed to the reduction of ash mortality by effectively reducing EAB densities in our study sites.

Technical Abstract: The emerald ash borer (Agrilus planipennis Fairmare, EAB) is an invasive buprestid that currently threatens North America’s native ash (Fraxinus spp.) resource, particularly the black ash (F. nigra Marshall) and green ash (F. pennsylvanica Marshall), which are common in riparian ecosystems and floodplain forests. Loss of these species has widespread implications for the ecosystems services these habitats provide. Biological control through the introduction of hymenopteran parasitoids from EAB’s native range in East Asia is a potential long-term management solution, however it is not known if the program can protect mature ash trees that often succumb to the initial wave of EAB invasion. We here assess the ash growth and survival response to EAB invasion at six floodplain forests in Massachusetts and the impacts of early releases of biological control agents, prior to significant ash mortality. We released the parasitoids Oobius agrili Zhang & Huang, Spathius galinae Belokobylskij, and Tetrastichus planipennisi Yang at three of the sites in 2017 through 2022. We then measured the DBH and assessed the canopy condition of approximately 100 tagged ash trees at each site from 2018 to 2024. We found that trees with greater initial canopy condition (higher dieback) were less likely to show significant growth, and we also found a significant effect of site. We also assessed the percent parasitism of EAB larvae through sentinel log monitoring and found a significant, negative correlation between percent parasitism in sentinel logs and proportion of ash mortality across our six sites. This is the first finding of a relationship between larval parasitism and ash health outcomes in the literature. Future work may seek to examine if similar outcomes can be found across different habitats and environments.