INTERACTION OF EVENING GROSBEAK (HESPERIPHONA VESPERTINA) AND SPRUCE BUDWORM (CHORISTONEURA FUMIFERANA (CLEM.)) IN A LOCALIZED BUDWORM OUTBREAK TREATED WITH DDT IN QUEBEC

Abstract

Control of a localized spruce budworm outbreak in southeastern Quebec was achieved through the combined effects of chemical treatment with DDT and natural control factors. Amongst the latter, predation by evening grosbeaks was suspected to have been of considerable importance. It appears that the birds were attracted to the outbreak area in unusually large numbers during their spring migration. The yearly influx of the grosbeaks in the area occurred when the budworm was in the late larval and the pupal stages, an especially critical period with respect to generation survival of this insect. In 1963, the year following collapse of the outbreak, very few grosbeaks were seen in the area. There was no direct evidence that the birds suffered ill effects from the spraying operation.