Factors affecting the biological control of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) by Coleomegilla maculata (DeGeer) (Coleoptera: Coccinellidae) in sweet corn

Coleomegilla maculata (DeGeer), which is a frequent predator of Helicoverpa zea (Boddie) eggs on sweet corn, prefers to oviposit on plants that have glandular trichomes. These plants provide C. maculata eggs a refuge from predation, leading to higher survival. Previous work showed that interplanting glandular pubescent weeds in sweet corn increases C. maculata density and predation on H. zea eggs. Tomato was demonstrated to be a preferred oviposition plant and refuge from egg predation for C. maculata in the same manner as glandular pubescent weeds. The effect of including tomato as a companion crop with sweet corn was discerned with a two-year field study. Significantly more C. maculata eggs were laid on tomato than on corn, and larval densities on sweet corn were augmented up to 5 m from the tomatoes. There was a trend for higher adult density in corn with companion tomato plants in one year of the study. Predation on pest eggs and percent of ears infested were not significantly different in the corn with a companion than in a corn monoculture.;Pest eggs in sweet corn with C. maculata larvae absent had significantly higher survival than in corn where they were present. Direct observations revealed that C. maculata larvae were the most frequent predators on pest eggs and were the cause of the lower survival of pest eggs when they were present. Only a small number of attacks by this natural enemy were observed during corn anthesis, at which time C. maculata adults were the most frequent predator of pest eggs. Larvae were observed significantly more often on the middle third of the plant and the corn leaves but occurred on all plant parts and heights. There was a trend towards higher survival of pest eggs at low density than at high densities which was significant in one of two years. Coleomegilla maculata often leaves the corn plant to pupate and was found significantly more on the common weed Acalypha ostryifolia Riddell than on corn. Larvae were not observed on this weed prior to pupation. Pupae had high survival rates on both the weed and on corn.;Key words. lady beetle, corn earworm, biological control, companion planting, natural enemy augmentation.