Mortality of European Corn Borer Larvae by Natural Enemies in Different Corn Microhabitats

Larvae of the European corn borer, Ostrinia nubilalis (Hubner), sustained high mortality in field corn, Zea mays L., in western Maryland. Mortality was highest in the first two larval stadia but varied greatly among larvae in different corn plant microhabitats. Predation, primarily by the anthocorid, Orius insidiosus (Say), was an important larval mortality factor whereas parasitism was minor. Young corn borer larvae in the relatively exposed microhabitats of whorls and leaf axils incurred higher mortality rates (respectively, 80 and 72%) than larvae concealed in ears (53%). Predation and undetermined causes were the key mortality factors of larvae in leaf axils. Predation alone, however, was the important factor affecting mortality in larvae inhabiting corn ears. Predators killed about 33% of seeond-generation first instar borer larvae in the leaf axils and ears and about 41% of first-generation first instar borer larvae in the whorls. Undetermined (residual) mortality factors (e.g., weather, host plant resistance, pathogens) had more impact on larvae in exposed microhabitats (whorls and leaf axils) than on larvae concealed in ears and stems. O. insidiosus appears to be the most important predator of corn borer larvae in western Maryland. The predator's population peaks coincide with corn pollen-shedding and silking. Then, the insect feeds on second-generation borer larvae as well as corn pollen in leaf axils. Successful biological control of corn borer larvae by O. insidiosus is therefore linked to both arthropod prey and corn pollen food sources. (c) 1992 Academic Press, Inc.