Cannibalism and interspecific predation: Role of oviposition behavior

Cannibalism and interspecific predation among insect predators are common, yet these behaviors are frequently omitted from predator-prey theory and empirical studies. Interactions among predators can disrupt, facilitate, or augment biological pest control. We estimated the relative strengths of cannibalism and interspecific predation in a maize-aphid-coccinellid predator system. We know from previous work that Adalia bipunctata females tend to oviposit at the top of the plant near large aphid aggregations and that Coleomegilla maculata females tend to oviposit at the bottom of the plant far from large aphid aggregations. We used this information to design experiments to estimate the relative strength of cannibalism and interspecific predation. At high aphid densities, eggs at the top of the plant, near aphids, were preyed upon more than eggs at the bottom of the plant, far from aphids. This result implies that A. bipunctata suffers greater egg mortality than C. maculata. In part, this was due to the foraging pattern of A. bipunctata and also the large populations of aphidophagous predators that develop as a result of the large aggregations of aphids at the top of the maize plant. In predator-enclosure experiments, A. bipunctata searched primarily near large aggregations of aphids and therefore fed more on eggs at the top of plants near large aggregations of aphids. C. maculata searched throughout, yet tended to feed on more eggs at the bottom of the plant. This demonstrated that for both species the effect of cannibalism was equal to or stronger than that of interspecific predation. These findings suggest that species-specific oviposition behaviors largely determined the relative strength of cannibalism and interspecific predation. Cannibalism and interspecific predation can be analyzed as interference competition. Using competition theory, we were able to make predictions about coccinellid species' joint impact on aphids and species dominance.