Selection and Evaluation of a Companion Plant to Indirectly Augment Densities of Coleomegilla maculata (Coleoptera: Coccinellidae) in Sweet Corn
2006
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 cannibalism and other predation. Previous work showed that interplanting glandular pubescent weeds in corn increases C. maculata density and predation on H. zea eggs. We conducted an oviposition preference screening to identify a cultivated species that could provide the same augmentation of C. maculata and possibly increase biological control. In our experiment, tomato had 2.5 times more C. maculata eggs found on it than Acalypha ostryifolia Ridell, a weed documented to be preferred for oviposition over corn. In a separate experiment, 9.6 times more C. maculata eggs were found on a tomato companion crop than on corn, and eggs on tomato had 2.6-5.9 times higher survival than those on corn. In corn plots with a companion crop of tomato, C. maculata larvae were 5-10 times more abundant near the companion crop than in an equivalent location in the corn monoculture. Augmentation of larval densities declined as distance from the companion tomato crop increased, but the augmentation effect persisted for at least 5 m away from the companion crop. In 1 yr of our study, there was a trend toward higher densities of C. maculata adults in the plots with a companion crop of tomato. The observed augmentation of C. maculata did not result in an increase in H. zea egg predation or decrease in ear infestation.
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