Effect of pollen on Coleomegilla maculata (Coleoptera: Coccinellidae) population density, predation, and cannibalism in sweet corn

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 pollen abundance on C. maculata population densities, predation by C. maculata on Helicoverpa zea (Boddie) eggs, and egg cannibalism by C. maculata. Plots designated as "no-pollen plots" were detasseled immediately before anthesis, whereas tassels were left intact in "pollen plots." In both years, when pollen 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 pollen and no-pollen plots. During anthesis in 1996, C. maculata egg and larval densities were significantly higher in pollen plots compared with no-pollen plots, but not in 1995. Predation on H. zea eggs was significantly lower in pollen plots than in no-pollen plots in 1995, but not in 1996. During anthesis in both years, egg cannibalism was lower in pollen plots compared with no-pollen plots and significantly so in 1996. EI en when abundant pollen led to increased C, maculata larval populations in pollen plots (i.e., in 1996), predation on H. zea eggs and cannibalism of C. maculata eggs was not higher in the pollen plots. suggesting that abundant pollen 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.