Microhabitat and resource selection of the European corn borer (Lepidoptera: Pyralidae) and its natural enemies in Maryland field corn

In western Maryland, the European corn borer, Ostrinia nubilalis (Hiibner), exhibited three flight periods (from late May to mid-September 1986-1988) but completed only two generations in corn. Oviposition by corn borer moths increased when the tassels emerged and shed pollen. Peak density of the predators Orius insidiosus (Say) and Coleomegilla maculata (DeGeer) coincided with peak density of the borer's second-generation eggs and neonates. Second-generation egg masses and second and older instars were randomly distributed between plants in the field where first instars were aggregated. Corn borer females of the second flight period deposited most eggs (82%) on the ventral surfaces of leaves in the middle sections of plants near silking ears (76.7%). The emerging neonates initially dispersed randomly on the leaves. However, 30 min after emergence, most neonates cued on leaf axils, which served as the most common microhabitat for young larvae. Larval microhabitat differed substantially between the nonoverwintering and overwintering forms and between early and late instars of the nonoverwintering form. Leaf axils were the preferred microhabitat of young larvae, but preference shifted to stalks and ears as larvae matured. Overwintering larvae inhabited almost only stalks. Similarly, O. insidiosus adults and nymphs changed their within-plant distribution throughout the season. These changes in the distribution of borer larvae and their predators are discussed in relation to prey and pollen availability in different corn plant microhabitats.