Mortality of emerald ash borer in urban populations in Ontario, Canada

Effective pest management strategies take into account the influence of natural mortality on the population dynamics of the target insect. Therefore an integrated management plan for emerald ash borer (EAB) requires the development of a stage-specific mortality schedule that quantifies the contribution of natural enemies in causing the death of larval EAB. We quantified mortality the causes of mortality in larval EAB from three early and mid-stage infestations in urban trees from three cities in Ontario, Canada. Between 2010 and 2011 we sampled 9 to 12 trees in each city. An additional 9 trees were sampled in one city in 2012. Sampling consisted of removing the bark from the sampled trees on all pieces > 10 cm in diameter and collecting All EAB larvae that were found. For each larvae we determined the stage and cause of mortality. Half the wood from all trees was reared for 6 weeks after sampling but before peeling to investigate the temporal effects of natural enemies. We found that the most larval mortality occurred in medium sized larvae (third and fourth instars) and appeared to be caused by interactions with the tree. There was little mortality caused by natural enemies. We observed a negative relationship between mortality and density, mortality decreased as density increased, but this relationship was mediated by the location within the tree where the larvae were developing. The results of this study can be used to model the impact of control measures on EAB populations in urban trees and to suggest what larval stages can be targeted to maximize the effect of suppression.