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Title: Temporal dynamics of woodpecker predation on the invasive emerald ash borer (Agrilus planipennis) in North America

item JENNINGS, DAVID - University Of Maryland
item Duan, Jian
item BAUER, LEAH - Us Forest Service (FS)
item Schmude, Jonathan
item WETHERINGTON, MILES - University Of Delaware
item SHREWSBURY, PAULA - University Of Maryland

Submitted to: Agricultural and Forest Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2015
Publication Date: 11/25/2016
Citation: Jennings, D.E., Duan, J.J., Bauer, L.S., Schmude, J.M., Wetherington, M.T., Shrewsbury, P.M. 2016. Temporal dynamics of woodpecker predation on the invasive emerald ash borer (Agrilus planipennis) in North America. Agricultural and Forest Entomology. 18:174–181.

Interpretive Summary: Emerald Ash borer (EAB) is a serious invasive forest pest in the United States, which has killed millions of North American ash trees and spread to 25 States since it was first detected in 2002 in South Michigan. Woodpeckers are important predators of EAB in North America. Understanding what types of ash trees and times of year that woodpeckers prefer to attack EAB should help to improve our predictions of how quickly EAB can spread, and how it can be more effectively managed. Therefore, scientists from USDA Agricultural Research Service, U.S. Forest Service, and University of Maryland conducted surveys of woodpecker predation on ash trees in Michigan and Maryland over several years, and examined how predation varied by season and by different tree characteristics. Woodpecker predation on EAB was most frequent in winter months, which coincided with when their preferred size of EAB larvae was most abundant. Woodpeckers also preferred to forage for EAB on unhealthier ash trees, but the size of these trees was generally less important. These findings will help foresters and land managers to develop sound EAB management strategies in light of seasonal patterns of woodpecker predations on EAB.

Technical Abstract: Woodpeckers (Picidae) are among the most prevalent natural enemies attacking the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire, in North America, but there can be considerable variation in the levels of EAB predation on ash trees (Oleaceae: Fraxinus) within and between sites as well as among different times of year. Understanding the temporal variations as well as factors causing these differences is important for predicting the role of these native predators in the population dynamics of EAB. In the present study, we examined the temporal dynamics of woodpecker predation on EAB, and how they were affected by season, region, resource availability, tree size, and crown condition. This work was conducted through separate surveys of woodpecker predation on EAB attacking ash trees in Michigan and Maryland. In Michigan, we quantified woodpecker predation in association with developmental stages of EAB on different trees in the spring, summer, and fall of 2009 and 2010. In Maryland, we recorded woodpecker predation on the same trees over the course of one year, as well as the diversity and abundance of woodpeckers at the sites. Our results showed that season was a significant predictor of the number of woodpecker attacks in Michigan and Maryland, with most woodpecker predation occurring in winter. This coincided with seasons when late-instar larvae, the overwintering stage of EAB (the preferred prey of woodpeckers), were most abundant. There was mixed support for the effect of DBH on predation, with some influence found in Michigan but not in Maryland. Our findings also indicated that predation appeared to be affected by the extent to which EAB generations were synchronized, which can vary among regions. This work demonstrates the importance of long-term studies of interactions between invasive species and native natural enemies to fully understand their dynamics.