QUANTIFYING THE IMPACT OF INSECT PREDATORS AND PARASITOIDS ON POPULATIONS OF THE APPLE ERMINE MOTH, YPONOMEUTA-MALINELLUS (LEPIDOPTERA, YPONOMEUTIDAE), IN EUROPE

Life tables were developed to assess the significance of natural enemi es on the dynamics of apple ermine moth, Yponomeuta malinellus Zeller, in southwestern Germany and to select parasitoid species for use in t he biological control of this pest in Canada. During the study from 19 93 to 1995 the abundance of Y. malinellus varied from 1.5 to 4.3 tents per 100 leaf clusters indicating that this was a non-outbreak populat ion. From the life tables it was evident that the impact of egg predat ors accounted for 25-43% of the total generational mortality of Y. mal inellus, more than any other known mortality factor. Percent parasitis m varied from 18 to 30%, but the impact of parasitoids in relation to the total generational mortality of Y. malinellus from the life tables was remarkably constant at 11-14%. The loss of potential fecundity ha d an important influence on the generational mortality of Y. malinellu s, but declined from 27% to 15% over the course of this study. This de cline corresponded with a rise in the net rate of increase R-0 from 1. 35 in 1993 to 6.8 in 1995, despite the impact of insect predators and parasitoids on the generational mortality. Yponomeuta malinellus was a ttacked by five different obligate primary parasitoids, a single oblig ate hyperparasitoid, and three facultative hyperparasitoids. Of these, the oligophagous egg-lan al parasitoid Ageniaspis fuscicollis Dalman (Encyrtidae) and the oligophagous larval-pupal and pupal parasitoid He rpestomus brunnicornis Gravenhorst (Ichneumonidae) were selected as po tential biological control agents for Canada due to a minimal degree o f interspecific competition.