Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2006
Publication Date: 4/5/2007
Citation: Cottrell, T.E. 2007. Predation by adult and larval lady beetles (Coleoptera: Coccinellidae) on initial contact with lady beetle eggs. Environmental Entomology. 36(2):390-401. Interpretive Summary: Lady beetles commonly cannibalize their eggs and prey upon the eggs of other lady beetle species. When the multicolored Asian lady beetle became established in North America, there was concern that this exotic species would negatively impact native lady beetle species. Indeed, laboratory studies have shown that this exotic species not only cannibalizes eggs, it does feed on the eggs of native species. This contrasts sharply with the native lady beetle species that predominantly attacked each other’s eggs. In this current study, it has been shown that the behavior of the lady beetle to attack or pass up an encountered egg cluster varies between species and by adult or larval stage. Overall, the exotic species fed on its eggs and native species’ eggs similarly upon initial encounters with eggs. This indicates that laboratory studies may not accurately gauge the impact of one species upon the other in the field.
Technical Abstract: Egg predation, predominantly cannnibalism, of lady beetle (Coleoptera: Coccinellidae) eggs is widely reported to occur in the field and under laboratory conditions. The recent establishment of the multicolored Asian lady beetle (Harmonia axyridis) has caused some concern given that this exotic species can feed on eggs of native lady beetle species whereas the native lady beetle species fed on this exotic species eggs at much lower rates and native larvae could not develop on a diet of those eggs. However, laboratory studies that investigate coccinellid egg predation are typically done over time and do not address what happens when an initial encounter is made by the predator with an egg cluster. In the current laboratory study, four native coccinellid species (Coleomegilla maculata, Cycloneda munda, Hippodamia convergens, and Olla v-nigrum) and one exotic species (H. axyridis) were tested to determine the predating species’ initial reaction (for both adults and larvae) to eggs of each species. A similar number of adults of the native C. maculata, C. munda and O. v-nigrum and the exotic H. axyridis consumed eggs of each species upon initial contact whereas initial consumption of the different species’ eggs by the native H. convergens was significantly different. Only larvae of the native C. maculata did not feed on the different species’ eggs at different rates upon initial contact. Surprisingly, field-collected adults of H. axyridis tended to reject most eggs, regardless of species, upon initial contact. Field-collected O. v-nigrum rejected most eggs of the other species but always cannibalized eggs upon initial contact. These results indicate that interactions among native and exotic lady beetle species in the field may be quite different than gauged solely from laboratory studies.