Quantifying the impact of insect predators and parasitoids on populations of the apple ermine moth,Yponomeuta malinellus(Lepidoptera: Yponomeutidae), in Europe

Abstract

AbstractLife tables were developed to assess the significance of natural enemies on the dynamics of apple ermine moth,Yponomeuta malinellusZeller, in southwestern Germany and to select parasitoid species for use in the biological control of this pest in Canada. During the study from 1993 to 1995 the abundance ofY. malinellusvaried from 1.5 to 4.3 tents per 100 leaf clusters indicating that this was a non-outbreak population. From the life tables it was evident that the impact of egg predators accounted for 25–43% of the total generational mortality ofY. malinellus, more than any other known mortality factor. Percent parasitism varied from 18 to 30%, but the impact of parasitoids in relation to the total generational mortality ofY. malinellusfrom the life tables was remarkably constant at 11–14%. The loss of potential fecundity had an important influence on the generational mortality ofY. malinellus, but declined from 27% to 15% over the course of this study. This decline corresponded with a rise in the net rate of increase R0from 1.35 in 1993 to 6.8 in 1995, despite the impact of insect predators and parasitoids on the generational mortality.Yponomeuta malinelluswas attacked by five different obligate primary parasitoids, a single obligate hyperparasitoid, and three facultative hyperparasitoids. Of these, the oligophagous egg-larval parasitoidAgeniaspis fuscicollisDalman (Encyrtidae) and the oligophagous larval-pupal and pupal parasitoidHerpestomus brunnicornisGravenhorst (Ichneumonidae) were selected as potential biological control agents for Canada due to a minimal degree of interspecific competition.