Cost of being an intraguild predator in predatory ladybirds

Survival and growth efficiency of fourth-instar larvae of two species of aphidophagous ladybirds, Coccinella septempunctata brucki Mulsant and Harmonia axyridis Pallas were determined when fed aphid, Acyrthosiphon pisum Harris, or intraguild prey, another species of aphidophagous ladybird, Propylea japonica Thunberg. The percentage of fourth instars fed intraguild prey that completed their development was 42.9% for C. septempunctata brucki and 100% for H. axyridis, respectively. All fourth-instar larvae of both species fed aphids completed their development. The average growth efficiency (increase in body weight/weight of prey consumed) of fourth instars of H. axyridis was significantly lower than that of C. septempunctata brucki when fed aphids. In contrast, when fed intraguild prey, it was significantly higher than that of C. septempunctata brucki. Adaptive significance and determinants of prey specialization in aphidophagous ladybirds are discussed.