Early responses of bark and wood boring beetles to an outbreak of the hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) in a boreal balsam fir forest of North America

Abstract

AbstractWe investigated the early responses of bark and wood boring beetles to an extensive supply of balsam fir (Abies balsamea) trees, stressed or recently killed during an outbreak of the hemlock looper (Lambdina fiscellaria) in Quebec, Canada. The present study aimed to (i) examine beetle assemblages across all levels of defoliation and (ii) assess the relative influences of defoliation, tree mortality, stand structure and spatial context on beetle assemblages. We used three types of traps in each of 36 plots: multidirectional flight interception traps measured adult beetle flight activity within stands, trunk window traps measured visitation rates at trees and emergence traps measured beetle colonization of trees. Flight traps in nondefoliated plots allowed characterization of ‘pre‐outbreak’ beetle assemblages, which were not discernable in emergence traps because few insects colonize heathy trees. ‘Pre‐outbreak’ assemblages, characterized by a mix of polyphagous beetle species (e.g. Evodinus monticola, Dryocoetes autographus), shifted to those dominated by Trypodendron lineatum after extensive defoliation. Two Pissodes species colonized heavily defoliated trees but not dead ones. Defoliation level, conifer basal area, basal area of dead balsam firs and the extent of recently logged areas around sampling plots were positively correlated with the abundance of T. lineatum.