Limitations ofTrichogramma nubilale(Hymenoptera: Trichogrammatidae) as an Inundative Biological Control ofOstrinia nubilalis(Lepidoptera: Crambidae)

Previous work indicated that Trichogramma nubilale Ertle & Davis could potentially be used as an inundative biological control of Ostrinia nubilalis in sweet corn, Zea mays L., in Minnesota. We expand on these observations to evaluate some of the factors that might limit the utility of T. nubilale in sweet corn and report on releases in green snap bean, Phaseolus vulgaris L. We conducted 3 releases in sweet corn and 2 releases in beans at LeSueur, MN, from 1990 to 1992. Between U.8 and 60.0 females per square meter of plant surface were released. Two-day egg parasitism varied between 2 and 60% in corn and 15 and 60% in beans. A meta-analysis of these results and several published experimental releases indicated that the major limitation in using T. nubilale is high variability in the relation between release rates and egg mass parasitism rates. This analysis also indicated that the relation between egg mass parasitism and larval population reduction was very strong, and that there was no evidence of density-dependent larval mortality. Thus, future work should focus on elucidating the factors causing variability in parasitism rates to improve the reliability of T. nubilale .