Effect of cannibalism and predation on the larval performance of two ladybird beetles

The relative impact of cannibalism and predation on the development and sur vival of fourth instar larvae was assessed in two species of aphidophagous ladybird beetles, Coccinella septempunctata and Harmonia axyridis. The effe ct of eating aphids, conspecific larvae or heterospecific larvae on larval performance differed in the two species: aphids were the best food for C. s eptempunctata and survival of C. septempunctata larvae was significantly lo wer when offered heterospecific larvae rather than conspecific larvae or ap hids as food, indicating that H. axyridis larvae were not suitable food for C. septempunctata. However, as the different foods did not affect the larv al performance of H. axyridis, this species appears to be more polyphagous. Both intraguild predation by the aggressive larvae of H. axyridis and the polyphagous food habit of this species may account for its dominance in lad ybird assemblages and its displacing other ladybird beetles in several plac es in the world.