Influence of Density of the European Corn Borer, Ostrinia nubilalis , (Lepidoptera: Pyralidae) on the Parasitoid Lydella thompsoni (Diptera: Tachinidae) 1

Field studies were conducted to assess the response of the European corn borer (ECB) parasitoid, Lydella thompsoni to four genotypes of corn and to varying host density. The application of one, two, and three egg masses per plant resulted in significant differences in corn borer populations. ECB populations also varied significantly with corn variety. A density-dependent response of the parasitoid was evident, although there was no difference among parasitism rates on the four genotypes of corn. Parasitism rates varied significantly with respect to the host's position on the plant as well as the plant's position within the plot. A higher rate of parasitism was evident for the top and middle portions of the plant than for the lower portion. Within the plot, there was a higher rate of parasitism in the center rows than in the bordering rows. Laboratory studies of parasitoids emerged from borers reared on various corn varieties indicated no significant difference in size, longevity, or fecundity.