Incidence of Heliothis zea (Lepidoptera: Noctuidae) and Associated Parasitoids in Virginia Soybeans

Abstract

Heliothis zea (Boddie) larvae and eggs were collected from soybean fields in five Virginia counties during 1987 and six counties in 1988. Microplitis croceipes (Cresson) was the predominant parasitoid associated with H. zea larvae throughout the study. Greater H. zea larval density and rates of parasitism were observed in fields planted after 10 June than in fields that were planted earlier. High levels of parasitism occurred only in fields where the presence of M. croceipes coincided with first appearance of host larvae. Most parasitoids emerged from H. zea larvae collected as third or fourth instars. No parasitoids emerged from H. zea larvae sampled from field corn, suggesting that M. croceipes populations in soybeans do not originate from H. zea hosts in corn fields. Despite warm holding temperature, 14% of the M. croceipes prepupae collected in 1987 entered diapause in the laboratory and emerged in August the following year. This is evidence for the hypothesis that M. croceipes overwinter in soybean fields and emerge in summer to coincide with first presence of H. zea larvae. Less than 4% of collected H. zea eggs were parasitized by Trichogrammatidae in Eastern Shore counties. However, high levelsof egg parasitism, >90% on some sample dates, occurred in fields in the Northern Neck.