RELATIONSHIPS BETWEEN SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) EGG MASS DENSITY AND RESULTANT DEFOLIATION OF BALSAM FIR AND WHITE SPRUCE

Abstract

AbstractAnnual spruce budworm, Choristoneura fumiferana (Clemens), survey data were subjected to multiple and logistic regression analyses to examine the relationship between egg mass density in the fall and resultant defoliation the next season. Egg mass density was the most important variable associated with resultant defoliation, followed by current defoliation, regional population trends, host species, and sprays. Together, these accounted for 60% of the variation in resultant defoliation. Balsam fir [Abies balsamea (L.) Miller] suffered greater levels of defoliation than white spruce [Picea glauca (Moench) Voss] at a given egg mass density. Resultant defoliation of balsam fir also showed a steeper response to egg mass density than resultant defoliation of white spruce. Levels of current defoliation increased susceptibility to defoliation in a similar manner between species, as did regional population trends. Sprays were more effective at reducing resultant defoliation on balsam fir than on white spruce but, overall, did not confer a high level of foliage protection. Predictions of resultant defoliation using the multiple regression models had confidence limits averaging 75%, which are too large to be useful for predictive purposes. The logistic regression equations could be used to predict the probability of a stand receiving light or severe defoliation.