Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/8/2005
Publication Date: 6/1/2005
Citation: Shapiro Ilan, D.I., Cottrell, T.E. 2005. Susceptibility of lady beetles (Coleoptera: Coccinellidae) to entomopathogenic nematodes. Journal of Invertebrate Pathology. 89:150-156. Interpretive Summary: Insect-killing nematodes are small round worms that kill insect pests but don't harm people or the environment. It is important to determine if these nematodes harm beneficial insects such as lady beetles. We tested the susceptibility of four lady beetle species to infection by two nematodes species. We found the lady beetles to be substantially less susceptible to nematode infection compared with a known susceptible insect (the black cutworm). Thus, we predict that the insecticidal nematodes will have minimal impact on lady beetles under field conditions. Among the lady beetle species, we observed higher susceptibility to nematode infection in exotically introduced lady beetles compared with native species. These findings suggest that lower susceptibility to native diseases may be one factor explaining why certain exotic biocontrol agents such as lady beetles have been able to competitively establish themselves in the USA.
Technical Abstract: We investigated differential susceptibility of lady beetles to the entomopathogenic nematodes, for two reasons: 1) to estimate potential non-target effects on natural lady beetle populations, 2) to compare the susceptibility of exotic lady beetle species with native lady beetle species. We hypothesize that successful establishment of some exotically introduced arthropods may be due, in part, to a lower pathogen susceptibility relative to competing native species. In laboratory studies, we compared the pathogenicity, virulence, and reproductive capacity of Heterorhabditis bacteriophora and Steinernema carpocapsae among two native (Coleomegilla maculata and Olla v-nigrum) and two exotic (Harmonia axyridis and Coccinella septempuncta) lady beetles, and a known susceptible pest species , Agrotis ipsilon. After exposure to nematodes, mortality of A. ipsilon was higher than in all lady beetles. Thus, we predict it is unlikely that entomopathogenic nematode applications would cause a notable negative impact to natural populations of the lady beetle species. Exotic lady beetles were less susceptible to nematode infection than endemic species. Overall, the hypothesis that low susceptibility to pathogens in certain exotic lady beetles may have contributed to competitive establishment was supported (especially H. axyridis). Additional laboratory and field studies incorporating different hosts and pathogens from various geographic locations will be required to further address the hypothesis.