Chris R. Hennigar, David A. MacLean
Faculty of Forestry and Environmental Management, University of New Brunswick

Chris J. Norfolk
NB Department of Natural Resources, Forest Mgmt. Branch,

SERG Project #2003/05
Year of Project: 2003
Report Received: 2005




The first major European gypsy moth (Lymantria dispar L.) outbreak occurred over 3000ha in central New Brunswick, Canada from 2001-2003. The outbreak was severe enough to result in considerable landowner concern and a privately-funded aerial insecticide spray program to protect trees. Defoliation was unexpectedly severe on several tree species thought to be resistant or immune from previous studies in the northeastern US, and thus 81 plots were established in stands to monitor population effects on defoliation (31 plots) and assess resulting growth reduction and mortality (50 plots). Egg-mass density to defoliation relationships were generally weak, due to low over-winter egg survival in 2002-2003 resulting in only light defoliation in most plots. After 2 years of severe defoliation, balsam fir (Abies balsamea (L.) Mill.) with defoliation >75% sustained growth reduction averaging 55% and 25% mortality. Red oak (Quercus rubra L.) sustained about 40% growth reduction, similar to results of previous studies. However, white birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) with >75% defoliation for 2 years sustained 43-48% growth reduction, higher than in previous studies, and 4-12% mortality. The gypsy moth range in Canada appears to be gradually expanding beyond previous climatic (cold winter temperature) limitations, and these results will help to predict future impacts.