Emerald ash borer density at three stages of the invasion wave

Emerald ash borer (EAB), (Agrilus planipennis Feirmaire) (Coleoptera: Buprestidae) first discovered in 2002, has killed millions of native ash (Fraxinus spp.) trees in forest, rural and urban settings in southern Michigan. Trees with low densities of EAB larvae exhibit few, if any, external symptoms. As EAB densities build, larval feeding disrupts the vascular system of trees, leading to canopy decline, progressive dieback and sprouting of epicormic shoots and trunk sprouts. As phloem is depleted and trees succumb, beetles disperse, resulting in an expanding area of catastrophic ash mortality. Questions consistently arise as to the status of EAB populations and the persistence of ash in forested settings in southern Michigan, particularly in the original core of the EAB infestation. We sampled EAB populations in 24 green ash (F. pennsylvanica) sites using double-decker traps, stressed trees and ash trees that were neither girdled nor baited. Eight sites were located in each of three areas of southern Michigan representing (1) the original EAB core, (2) stands where EAB populations are currently peaking and (3) southwestern forests where EAB has recently become established. Species composition and condition of overstory trees were quantified and regeneration sampled in each of the 24 sites.