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Submitted to: Biological Control
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/18/2005 Publication Date: 5/31/2005 Citation: Cottrell, T.E. 2005. Predation and cannibalism of lady beetle eggs by adult lady beetles. Biological Control. 34:159-164. Interpretive Summary: The recently introduced multicolored Asian lady beetle has become established in many habitats over much of North America. Previous studies have shown that this exotic species could compete with, and negatively impact, local populations of native lady beetle species. An examination of predation on lady beetle eggs of native and exotic species showed that native species, Coleomegilla maculata and Olla v-nigrum, always attacked a fewer eggs of the exotic species. Each native species attacked eggs from both native species at similar rates and tended to entirely consume those attacked eggs. However, native species attacked eggs of the exotic species at a lower rate and left many of those eggs partially consumed. The exotic species attacked native and exotic eggs at similar rates and left only a low percentage of any species' eggs partially consumed. If an alternative food source, e.g., aphids, is present, native species fed less on their own species' eggs than if an alternative food was not provided. This difference was not statistically significant when the exotic species fed on its own species eggs but was significant when it fed on eggs of either native species. For native species, egg predation was significantly reduced by the presence an alternative food source for O. v-nigrum adults but not C. maculata adults. The presence/absence of an alternative food source had no significant effect upon the low percentage of interspecific predation by either native species on H. axyridis eggs. When aphid populations decline, native lady beetle eggs will suffer predation from both native species and the exotic species, whereas the exotic species will be exposed primarily to egg cannibalism. Technical Abstract: The exotic Harmonia axyridis has become established in many habitats over much of North America. Previous studies have shown that this species is a strong intraguild competitor and could negatively impact local populations of native Coccinellidae. A laboratory examination of inter- and intraspecific egg predation by groups (mixed-sex, female, and male) of exotic (H. axyridis) and native (Coleomegilla maculata and Olla v-nigrum) adult Coccinellidae revealed that native species always attacked a lower percentage of H. axyridis eggs than inter- and intraspecific egg predation among the native species. This difference was significant for mixed-sex C. maculata and O. v-nigrum, female O. v-nigrum, and male O. v-nigrum. Intraspecific egg predation by H. axyridis was significantly higher than H. axyridis interspecific predation by the following: mixed-sex group on C. maculata eggs, female group on O. v-nigrum eggs and the male group on both C. maculata and O. v-nigrum eggs. Native species attacked native eggs at similar rates and tended to entirely consume attacked eggs, however, native species attacked H. axyridis eggs at a lower rate and left many eggs partially consumed. H. axyridis attacked native and exotic eggs at similar rates and left only a low percentage of any species' eggs partially consumed. When provided an alternative food, intraspecific egg predation was significantly reduced for each native species and nearly so for H. axyridis. Interspecific egg predation by H. axyridis was significantly reduced by the presence of an alternative food. Between the native species, interspecific egg predation was significantly reduced by the presence an alternative food source for O. v-nigrum adults but not C. maculata adults. The presence/absence of an alternative food source had no significant effect upon the low percentage of interspecific predation by either native species on H. axyridis eggs. Thus, in situations of low food availability, native coccinellid eggs will suffer from both inter- and intraspecific predation whereas intraspecific egg predation is the larger threat to H. axyridis. |
