Influence of Host Stress on Emerald Ash Borer (Coleoptera: Buprestidae) Adult Density, Development, and Distribution in Fraxinus pennsylvanica Trees

ABSTRACT Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), a phloem-feeding beetle native to East Asia, was first discovered in southeast Michigan and Essex County, Ontario, in June 2002 and has since killed millions of ash (Fraxinus spp.) trees in North America. Initial studies in southeast Michigan indicated that the life cycle of A. planipennis was univoltine but more recent observations indicated some larvae feed for two summers, resulting in a 2-yr life cycle. Understanding factors that affect A. planipennis attraction to and development on host trees could improve detection and predictions of its population dynamics. We assessed adult A. planipennis attraction and larval density, distribution, and development rates in 2006 and 2007 on pole-sized green ash (Fraxinus pennsylvanica Marshall) trees that were girdled, exposed to the stress-elicitor methyl jasmonate, or left untreated. The study was conducted in a homogenous plantation with low levels of infestation. Overall, adult captures increased fivefold and four times as many larvae were recorded in 2007 compared with 2006. In both years, girdled trees captured significantly more adult A. planipennis, had higher larval densities, and larvae developed faster than on untreated control trees or trees exposed to methyl jasmonate. In 2006, larvae feeding below the girdle developed significantly faster than larvae feeding above the girdle. Adult A. planipennis captures, larval density and development did not differ significantly between untreated trees and trees exposed to methyl jasmonate in either year.