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Title: Biotic mortality factors affecting emerald ash borer (Agrilus planipennis) are highly dependent on life stage and host tree crown condition

Author
item JENNINGS, DAVID - University Of Maryland
item Duan, Jian
item SHREWSBURY, PAULA - University Of Maryland

Submitted to: Bulletin of Entomological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2015
Publication Date: 6/1/2015
Citation: Jennings, D.E., Duan, J.J., Shrewsbury, P.M. 2015. Biotic mortality factors affecting emerald ash borer (Agrilus planipennis) are highly dependent on life stage and host tree crown condition. Bulletin of Entomological Research. 1-9.

Interpretive Summary: Emerald ash borer (EAB), Agrilus planipennis, is a devastating invasive beetle that was accidentally introduced to the United States in the 1990s and has subsequently killed millions of ash trees (Fraxinus spp.) in this country. Resistance from host trees and attacks by EAB natural enemies (e.g., woodpeckers and parasitic wasps) are known killers in their native range in Asia, but how that works in the U.S. is not clear. To improve resistance to EAB, scientists at ARS and University of Maryland conducted a two-year experiment in 12 natural ash stands in Maryland. We found that in healthy trees, trees with a low EAB infestation, tree resistance was responsible for killing the most EAB larvae; but in more stressed trees, trees with a moderate to high infestation of later stages of EAB larvae, parasitism from parasitic wasps and predation from woodpeckers were responsible for killing the most larvae. Our findings provide a useful approach to controlling EAB in the United States.

Technical Abstract: Emerald ash borer (EAB), Agrilus planipennis, is a serious invasive forest pest in North America responsible for killing tens to hundreds of millions of ash trees since it was accidentally introduced in the 1990’s. Although host plant resistance and natural enemies are known to be important sources of mortality for EAB in Asia, less is known about the importance of different sources of mortality at recently colonized sites in the invaded range of EAB, and how these relate to host tree crown condition. To address this deficiency in knowledge, we used a large-scale field experiment and life table analyses to quantify the fates of EAB larvae and the relative importance of different biotic mortality factors on EAB population dynamics at recently colonized sites in Maryland. We found that the fates of larvae were highly dependent on EAB life stage, and host tree crown condition. In relatively healthy trees (i.e., with a low EAB infestation) and for early instars, host tree resistance was the most important mortality factor. Conversely, in more stressed trees (i.e., with a moderate to high EAB infestation) and for later instars, parasitism and predation were the major sources of mortality. Life table analyses also indicated how the lack of sufficient levels of host tree resistance and natural enemies contribute to rapid population growth of EAB at recently colonized sites. Our findings provide further evidence for the mechanisms by which EAB has been able to successfully establish and spread in North America.