Effects of indigenous ladybird species (Coleoptera: Coccinellidae) on the survival of an exotic species in relation to prey abundance

Interspecific relationships between indigenous ladybird species, Coccinella septempunctata L,. and Harmonia axyridis Pallas, and an exotic species, Adalia bipunctata (L.), were assessed in relation to prey abundance. The nature and relative strengths of interactions between indigenous and exotic ladybird species differed in relation to prey availability and species involved. Under conditions of high prey abundance, the negative effect of interactions was limited to slower larval development of A. bipunctata in the presence of H. axyridis larvae. Under conditions of limited food availability, intraguild predation often occurred and C. septempunctata and H. axyridis were intraguild predators and A. bipunctata was intraguild prey. H. axyridis larvae was a stronger intraguild predator of A. bipunctata than C. septempunctata larvae. Possible causes for limited habitat of A. bipunctata after invasion into Japan, and the decrease in abundance of native populations of A. bipunctata in the U.S.A. after introduction of C. septempunctata and H. axyridis are discussed in relation to interactions of A. bipunctata with C. septempunctata and H, axyridis.