Effects of indigenous ladybird species (Coleoptera : Coccinellidae) on thesurvival 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, Ad alia bipunctata (L.), were assessed in relation to prey abundance. The natu re and relative strengths of interactions between indigenous and exotic lad ybird species differed in relation to prey availability and species involve d. Under conditions of high prey abundance, the negative effect of interact ions was limited to slower larval development of A. bipunctata in the prese nce of H. axyridis larvae. Under conditions of limited food availability, i ntraguild predation often occurred and C. septempunctata and H. axyridis we re intraguild predators and A. bipunctata was intraguild prey. H. axyridis larvae was a stronger intraguild predator of A. bipunctata than C. septempu nctata larvae. Possible causes for limited habitat of A. bipunctata after i nvasion 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.