Generalist arthropod predators can have enormous influences on the population dynamics of target prey, yet the presence of alternative foods often influences predator foraging behavior and makes it difficult to predict the ultimate change in predation of a target pest. To investigate the effects of alternative food on predation of European corn borer eggs, we studied the polyphagous coccinellid Coleomegilla maculata DeGeer and its most common alternative foods in Minnesota maize: corn leaf aphids and corn pollen. Using field cages and open plot experiments, we determined that aphids and pollen do influence predation of corn borer eggs.
Suitability feeding studies and preference experiments were performed in the laboratory to interpret predation in the field. However, the results were not consistent with field predation patterns. Nutritional studies suggested pollen was a marginal food source, yet in the field pollen reduced predation on eggs by half. Simple preference experiments revealed egg predation is drastically reduced when aphids are present. However, in field experiments aphids had little overall effect on corn borer egg predation.
A spatial model and experimental observations of C. maculata foraging predict that the distribution of foods in relation to predator movement can account for these seemingly counterintuitive results. Pollen is abundant throughout the plant’s surface where it is frequently contacted by predators and provides frequent distractions. The more concentrated aphid colonies are less frequently contacted during C. maculata foraging on corn. Even when aphids are contacted, the time spent eating them is balanced by an increase in localized foraging and therefore increased contacts with eggs. By understanding the most important influences on foraging behavior and movement we can predict how to manage alternative foods to maximize predation on target pest species by generalist predators.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA