BIOLOGY AND ECOLOGY OF HERPESTOMUS-BRUNNICORNIS (HYMENOPTERA, ICHNEUMONIDAE), A POTENTIAL BIOLOGICAL-CONTROL AGENT OF THE APPLE ERMINE MOTH(LEPIDOPTERA, YPONOMEUTIDAE)

Fourth and fifth instar larvae, and also pupae of the apple ermine mot h, Yponomeuta malinellus Zeller, are attacked by the ichneumonid Herpe stomus brunnicornis Gravenhorst in central Europe. The parasitoid was studied as a potential biological control agent of the apple ermine mo th in British Columbia. Investigations of the biology of H. brunnicorn is, its distribution of attack within the tree canopy and the rate of parasitism in relation to spatial variation in the number of hosts per tent were studied over a 4 year period in Europe. The following biolo gical parameters of H. brunnicornis were studied: adult emergence, sex ratio, copulation, potential fecundity per day, host feeding, oviposi tion behaviour, handling time, and larval and pupal development. In th e present study, the number of tents of the apple ermine moth varied f rom 0.5 to 1.3 per 30-leaf cluster and pupal parasitism by H. brunnico rnis ranged from 3.9% to 8.5% in 1993-1995. Host tents were randomly d istributed within and between apple trees. No significant differences were found between the number of emerging H. brunnicornis per tent and the four directional quadrants within the tree canopy in 1993-1995. T he index of dispersion indicated that the distribution of emerging par asitoids per host tent was contagious. Percentage parasitism between t ents by H. brunnicornis was inversely related to the number of host la rvae/pupae per tent. Herpestomus brunnicornis is a synovigenic parasit oid whose females have a small maximum egg load. in addition, handling time on host pupae is high. Both these characteristics appear to prov ide an adequate explanation for the inverse density-dependence in para sitism on a spatial scale.