On intra-guild predation and cannibalism in Harmonia axyridis (Pallas) and Adalia bipunctata L. (Coleoptera: Coccinellidae) Giovanni Burgio, * Fabrizio Santi, and Stefano Maini DiSTA—Entomologia, via F. Re 6, 40126, Universit  a di Bologna, Bologna 40126, Italy Received 29 January 2001; accepted 28 January 2002 Abstract 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 °C 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. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Coccinellidae; Harmonia axyridis; Adalia bipunctata; Intra-guild predation; Cannibalism 1. Introduction Several reviews have addressed the issues of non- target impacts of biocontrol (Howarth, 1997; Pimentel et al., 1994; Samways, 1994; Simberloff and Stiling, 1996; Wajnberg et al., 2001). Negative impacts of in- troduced exotics include competitive suppression or displacement of native natural enemies and suppression or extinction of non-target prey species, some of which may be beneficial (Elliott et al., 1996). Lynch et al. (2001) recently collected data relating to introductions of both insect and microbial agents against insect pests, including classical and augmentative biocontrol. Con- version of the descriptions of non-target effects into a more objective severity scale would allow a quantitative summary of recorded non-target effects to be made which will provide a useful basis for future research into side effects. Several species of predatory Coccinellidae are used in biological control against introduced prey and the effi- ciency of these beneficials has often been demonstrated in crops (Hodek and Honek, 1996; Ferran et al., 1996). Because of spatial and temporal co-occurrence and po- lyphagous habits of exotic species, there is potential for intra-guild predation (IGP), defined as ‘‘the killing and eating of species that use similar, often limiting, re- sources and are thus potential competitors’’ (Polis et al., 1989). Such predator-predator interactions are thought to decrease the efficacy of biological control (Rosenheim et al., 1995). The Asiatic polyphagous ladybird Harmonia axyridis (Pallas) was introduced to France by the I.N.R.A. (Ferran et al., 1996), United States (Brown, 1999; Brown and Miller, 1998; Colunga-Garcia and Gage, 1998; La- Mana and Miller, 1996) and Canada (Coderre et al., 1995). Field surveys in West Virginia (USA) by Brown Biological Control 24 (2002) 110–116 www.academicpress.com * Corresponding author. Fax: + 39-051-251052. E-mail address: gburgio@entom.agrsci.unibo.it (G. Burgio). 1049-9644/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII:S1049-9644(02)00023-3