Parasite Studies in Two Residual Spruce Budworm (Choristoneura fumiferana (Clem.)) Outbreaks in Quebec

Abstract

AbstractParasite studies were carried out in two residual spruce budworm outbreaks in Quebec. Investigations were conducted during the last three years of the outbreak in the Lower St. Lawrence region and during the last year of the one in the Saguenay region. In the Lower St. Lawrence region decline of the insect population was initiated through aerial application of DDT over a period of three years, while in the Saguenay region the unfavourable condition of the forest stands apparently kept budworm numbers below peak outbreak levels. The incidence of mortality through the action of parasites was very high during the last year of both of these outbreaks and probably contributed to bringing about their collapse. Meteorus trachynotus Vier. has repeatedly been recovered in abundance during the last year of a number of budworm outbreaks and it was amongst the important parasites recovered in both outbreaks under discussion. Other species, however, that were abundant in one or the other of these two outbreaks had not been recovered in numbers before. The parasite complex and the relative abundance of each parasite species during budworm outbreaks is fairly constant at the time of peak host populations, but it is now apparent that they vary considerably at the time of outbreak collapse. Variations in the presence and relative abundance of alternate hosts probably account for this situation.