Effect of Pollen on Coleomegilla maculata (Coleoptera: Coccinellidae) Population Density, Predation, and Cannibalism in Sweet Corn

Abstract

Coleomegilla maculata (DeGeer) is an abundant, polyphagous predator in corn fields; it can develop and reproduce on a diet of only corn pollen. We used sweet corn ( Zea mays L.) in field experiments to investigate the effect of abundance on C. maculata population densities, predation by C. maculata on Helicoverpa zea (Boddie) eggs, and egg cannibalism by C. maculata . Plots designated as were detasseled immediately before anthesis, whereas tassels were left intact in pollen In both years, when was absent in all plots (i.e., before and after anthesis) there were no significant differences in C. maculata population density, H. zea egg predation, or C. maculata egg cannibalism between and no-pollen plots. During anthesis in 1996, C. maculata egg and larval densities were significantly higher in plots compared with no-pollen plots, but not in 1995. Predation on H. zea eggs was significantly lower in plots than in no-pollen plots in 1995, but not in 1996. During anthesis in both years, egg cannibalism was lower in plots compared with no-pollen plots and significantly so in 1996. Even when abundant led to increased C. maculata larval populations in plots (i.e., in 1996), predation on H. zea eggs and cannibalism of C. maculata eggs was not higher in the plots, suggesting that abundant diverts C. maculata from carnivory. Thus, even though C. maculata populations may increase during anthesis in corn, this increased abundance is not likely to translate into increased predation on H. zea eggs.