Potential impacts of emerald ash borer biocontrol on ash health and recovery in southern Michigan

Authors: KASHIAN, DANIEL - Wayne State University; BAUER, LEAH - Us Forest Service (FS); SPEI, BENJAMIN - Wayne State University; Duan, Jian; GOULD, JULI - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Forests
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2018
Publication Date: 5/25/2018
Citation: Kashian, D.M., Bauer, L.S., Spei, B.A., Duan, J.J., Gould, J.R. 2018. Potential impacts of emerald ash borer biocontrol on ash health and recovery in southern Michigan. Forests. 9(6):296. https://doi.org/10.3390/f9060296.
DOI: https://doi.org/10.3390/f9060296

Interpretive Summary: The emerald ash borer (EAB) is a serious invasive forest pest that has killed tens of millions of ash trees in the United States and Canada. A biological control program was initiated against this destructive pest of ash trees (Fraxinus spp.) in 2007 after U.S. federal regulatory agencies approved release of three biocontrol agents (parasitic wasps) in EAB-invaded areas. Scientists from the USDA ARS Beneficial Insects Introduction Research Unit (Newark, Delaware), Wayne State University, the USDA Forest Service, and USDA APHIS monitored changes in the health and regeneration of ash where EAB biocontrol agents have been released. Findings from the study showed that ash regeneration was highly variable among different study sites but was generally higher in biocontrol release plots compared to control plots, suggesting some protection of ash saplings from EAB by the biocontrol agents.

Technical Abstract: Emerald ash borer (EAB) is an invasive beetle that kills native North American ash species, threatening their persistence. A classical biological control program for EAB was initiated in 2007 with the release of three specialized EAB parasitoids. Monitoring changes in the health and regeneration of ash where EAB biocontrol agents have been released is critical for assessing the success of EAB biocontrol and predicting future changes to the ash component. We sampled release and control plots across southern Michigan over a three-year period to measure ash health and recruitment as a first attempt to assess the long-term impact of EAB biological control on ash populations. We noted reduced mortality of larger trees between 2012 and 2015 in release plots compared to control plots and increases in ash diameter, but our results were otherwise inconsistent. Ash regeneration was highly variable among study sites but was generally higher in release plots compared to control plots, suggesting some protection of ash saplings from EAB by parasitoids. We conclude that EAB biocontrol is likely to have a positive effect on ash populations, but that the study duration was not long enough to definitively deduce the long-term success of the biocontrol program in this region.