Bulletin of Insectology 56 (2): 207-210, 2003 ISSN 1721-8861 Intra-guild predation and cannibalism of Harmonia axyridis and Adalia bipunctata in choice conditions Fabrizio SANTI, Giovanni BURGIO, Stefano MAINI Dipartimento di Scienze e Tecnologie Agroambientali - Entomologia, Università di Bologna, Italy Abstract A laboratory experiment was carried out to examine intra-guild predation and cannibalism of exotic Harmonia axyridis (Pallas) and the native species Adalia bipunctata L. (Coleoptera Coccinellidae) in choice condition. Experiments were carried out in glass petri dishes at 25°C, 70% RH, using a 5x4 grid with 10 eggs of exotic and 10 of natives arranged alternatively. One larva or adult of coccinellid was put in the arena and was observed for one hour. Each experiment was replicated 15 times. H. axyridis larvae and adults, and A. bipunctata adults, showed a preference to prey and eat their own eggs rather than interspecific eggs; these dif- ferences were detected for both naive and experienced females and larvae. For A. bipunctata larvae no differences were observed between IGP and CANN in choice conditions. The results indicate a tendency for both species to attack and eat their own eggs rather than interspecific eggs. The risk of introduction of exotic generalist predators is discussed, with particular attention to coc- cinellids. Laboratory experiments on intra-guild predation could give a preliminary indication of the potential for competition between an exotic ladybird and a native one. Key words: Adalia bipunctata, cannibalism, choice test, Harmonia axyridis, intra-guild predation, biological control. Introduction cinellidae) were examined in laboratory experiments in no choice condition on eggs and on larvae (Burgio et The Asiatic polyphagous ladybird Harmonia axyridis al., 2002; Burgio et al., submitted for publication). IGP (Pallas) (Coleoptera Coccinellidae) is a Palearctic spe- competition was investigated by determining the con- cies originating from the far East; the beetle occurs in sumption of interspecific and CANN eggs by fourth in- Korea, Japan, Bonin Islands, China, Himalayas, For- star larvae and adult females, because prey suitability mosa, Siberia (Iablokoff-Khnzorian, 1982). This species may be an indicator of the likelihood that the prey was introduced and established in United States (La- would be attacked in the field (Phoofolo and Obrycki, Mana and Miller, 1996; Brown and Miller, 1998; Col- 1998); and could give a preliminary indication of the unga-Garcia and Gage, 1998; Brown, 1999), Canada potential for competition between an exotic ladybird (Coderre et al., 1995) and released in European coun- and a native one. The bioassays indicate that H. axyridis tries like France (Ferran et al., 1996) and Italy mainly to does not demonstrate IGP vs. native species at a higher control aphids damaging protected crops. level than CANN of native species. It appears that H. Because of polyphagous habits of these species of coc- axyridis does show a high potential for CANN and cinellids, there is potential for intra-guild predation therefore seems unlikely this species will to have a (IGP), defined as “the killing and eating of species that negative impact on native species by IGP of eggs (Bur- use similar, often limiting, resources and are thus po- gio et al., 2002). tential competitors” (Polis et al., 1989). Predator- The aim of this laboratory study was to examine IGP predator interactions, as reported by Rosenheim et al. and CANN of exotic H. axyridis and the native species (1993), may reduce the biocontrol. Classic biocontrol, A. bipunctata in choice condition and viceversa. Further that lies on introduction of exotic beneficial insect, in data regarding the possibility that IGP and CANN de- these cases may not increase Coccinellidae species and pend by the preconditioning of the individuals were also population abundance and may therefore not have a net taken into account. CANN is a quite common behaviour effect on biological control of aphid pests (Elliott et al., in ladybirds and we try to evince a difference between 1996). Lynch et al. (2001) collected data relating to in- naive or experienced individuals (larvae and adults) on troductions of both insect and microbial agents against their own species prey or IGP. insect pests, including classical and augmentative bio- control. Recently a methodology for risk assessment has been developed by van Lenteren et al. (2003) as a basis Materials and Methods for regulation of import and release of exotic natural enemies used in inundative forms of biocontrol; the pa- Predatory species utilised in the experiment were H. per proposes a general framework of a risk assessment axyridis (starting material from a biofactory and reared methodology for biological control agents, integrating for more than 10 generations in laboratory) and the na- information on the potential of an agent to establish, its tive species A. bipunctata collected in the field and then abilities to disperse, its host range, and its direct and in- reared in laboratory at least for 4 generations. Ladybird direct effects on non-targets. larvae of both species were feed with frozen eggs of In a previous paper, IGP and cannibalism (CANN) of Ephestia kuehniella (Zeller) (Lepidoptera Crambidae) H. axyridis and Adalia bipunctata L. (Coleoptera Coc- The adults were fed on aphids [Myzus persicae (Sulzer) 207 (Rhynchota Aphididae) on beans plants]. adults, and the CANN data were near to reach the sig- Experiments were carried out in glass petri dishes nificance level (P = 0.053). For A. bipunctata adults, no (12cm diameter) at 25°C, 70% RH, using a 5x4 grid differences were detected for IGP and CANN, between with 10 eggs of exotic and 10 of natives arranged alter- naive and experienced females. For A. bipunctata lar- natively. One larva or adult of coccinellid was put in the vae, on the contrary of what was detected on H. axy- arena and was observed for one hour. Each experiment ridis, the IGP (P = 0.056) and CANN (P = 0.044) were was replicated 15 times. The sets of experiments in- higher in naive rather in experienced females. Anyway cluded: 1) naive females and larvae; 2) experienced fe- the level of egg consumption in these cases was very males and larvae. To obtain experienced larvae and fe- low and the P values were very close to the level of 5%; males we put the specimens in a petri dish for 4 hours moreover the high standard deviations demonstrate a with eggs of both species. Only the individuals that consistent variability in these latter parameters. were observed to eat at least 4 eggs of exotic and 4 eggs In general, in the experiments with larvae there was of native were considered as experienced. As "eaten" clearly a low level of egg CANN and IGP for both ex- were considered the eggs partially or completed wolfed otic and native species. Moreover for indigenous lady- down. The "rejected" were eggs that after a contact by bird adults and larvae, the consumption of interspecific mouthparts and antennae were drastically refused. eggs was lowest in comparison with the consumption of For each species and stage data were analysed in order interspecific eggs by the exotic species. to: For H. axyridis experienced adults and larvae, rejec- - compare the mean number of intraspecific eggs tions of interspecific eggs were highest in comparison eaten vs mean number of interspecific; with rejections of intraspecific eggs (table 2). The same - compare the mean number of intraspecific eggs re- observation for adults and larvae of the native ladybird, jected vs mean number of interspecific. i.e. the rejections in case of IGP were highest in com- Data were analysed by Wilcoxon matched pairs test parison of rejections of CANN both for naive or experi- (P < 0.05) to compare, for a species, egg consumption enced individuals. The differences were not significant and egg rejection of intraspecific vs interspecific prey. for A. bipunctata experienced larvae, also if P values The comparison, for a species, of IGP and CANN in were slightly higher to the level of 5% (table 2). naive vs experienced females was analysed by Mann- The results indicate a tendency for both species to at- Whytney U test (Zar, 1984). tack and eat their own eggs rather than interspecific eggs confirming the results in no choice condition ex- periments (Burgio et al., 2002). For A. bipunctata lar- Results and discussion vae no differences were detected between IGP and can- nibalism. The predation of eggs was dependent by the H. axyridis larvae and adults, and A. bipunctata adults preconditioning of the individuals: for larvae of exotic showed a preference to prey and eat their own eggs species both IGP and CANN were significantly higher rather than interspecific eggs (table 1); these differences in experienced vs naive. Naive adults of the exotic spe- were detected for both naive and experienced females cies showed an IGP not statistically different in com- and larvae. For A. bipunctata larvae no differences were parison with experienced adults, but CANN in experi- observed between IGP and CANN in choice conditions enced adult females was higher in comparison with na- (table 1). For H. axyridis larvae, both IGP and CANN ive females. For indigenous species adults and larvae were significantly higher in experienced vs naive (table the consumption of interspecific eggs was in general 1). Naive adults of the exotic species showed an IGP not lowest in comparison with the consumption of inter- statistically different in comparison with experienced specific eggs by exotic. Table 1. Summary of the results of the choice test. Numbers indicate the mean of eggs eaten per female ± standard deviations. Line comparisons analized by Mann-Whytney U test; row comparisons analized by Wilcoxon’s signed- Rank test. Species Stage Behaviour Naive Experienced P H. axyridis Adult CANN 3.8 ± 2.3 5.5 ± 2.7 0.053 H.