On intra-guild predation and cannibalism in Harmonia axyridis (Pallas) and Adalia bipunctata L. (Coleoptera: Coccinellidae)

Interspecific competition between the exotic coccinellid Harmonia axyridis (Pallas) and the native species Adalia bipunctata L. was investigated in the laboratory by determining the consumption of interspecific eggs by fourth instar larvae and adult females. Larvae and adult ladybirds were individually put into petri dishes at 25 degreesC with 20 eggs of the selected target species. The tests included three treatments: (a) only coccinellid eggs, (b) coccinellid eggs and 5 aphids, and (c) coccinellid eggs and 40 aphids. Intra-guild predation (IGP) by H. axyridis of eggs of the native species, A. bipunctata, was lower in comparison with egg cannibalism (CANN) by H. axyridis, for both adults and larvae. No differences were detected for larvae at the density of 5 aphids. IGP of exotic against the native species was never higher than CANN of native species. IGP of native species was never higher in comparison with CANN. A. bipunctata adult CANN was significantly higher than IGP at densities of 0 and 40 aphids. In the set of experiments on CANN and IGP an inverse correlation was observed between egg consumption by adults and larvae and aphid density. Our bioassays indicate that H. axyridis does not demonstrate IGP vs. native species at a higher level than CANN of native species. It appears that H. axyridis does show a high potential for CANN and therefore seems unlikely this species will to have a negative impact on native species by IGP of eggs. (C) 2002 Elsevier Science (USA). All rights reserved.