Emerald ash borer (Agrilus planipennis) (EAB), a phloem-feeding beetle native to East Asia, was first discovered in southeastern Michigan and Essex County, Ontario in June 2002. Little information about the biology and behavior of EAB larvae was available from its native range. A better understanding of EAB biology is important for developing effective detection methods and accurate models of population dynamics. We assessed the effects of host vigor on larval distribution, survival and development rates on 90 ash (Fraxinus sp.) trees in 2006 and again in 2007 in a plantation with a low density of EAB. Each year, trees were randomly to be girdled (30 trees), exposed to the stress eliciting hormone methyl jasmonate (30 trees) or left untreated (30 trees). Trees were felled and dissected during the fall and winter to quantify larval density and related variables. In both 2006 and 2007, mean larval density and development rates were significantly higher on girdled trees than other trees. Woodpecker predation of 4th instars was the most common cause of larval mortality.