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Title: Susceptibility of endemic and exotic North American lady birds (Coleoptera: Coccinellidae) to endemic fungal entomopathogens

item Cottrell, Ted
item Shapiro Ilan, David

Submitted to: European Journal of Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2007
Publication Date: 7/31/2008
Citation: Cottrell, T.E., Shapiro Ilan, D.I. 2008. Susceptibility of endemic and exotic North American lady birds (Coleoptera: Coccinellidae) to endemic fungal entomopathogens. European Journal of Entomology. 105(3): 455-460.

Interpretive Summary: In this study, we determined the susceptibility of four species of native North American lady beetles to different isolates of the ubiquitous insect pathogenic fungus, Beauveria bassiana. Results from this study will provide information on the role of pathogens attacking lady beetle predators and also how pathogens might influence the establishment of introduced species. The B. bassiana isolates used in this study were derived from 1) a naturally-infected native lady beetle, 2) a commercially-available, fungus-based insecticide and 3) the soil in a pecan orchard. Our results showed that the source of the fungus was important regarding its impact upon lady beetles. None of the four native species were susceptible to low rates of the fungus derived from the formulated product nor from the isolate obtained from a pecan orchard. However, the fungus isolate obtained from a naturally-infected lady beetle was highly pathogenic to two native species, moderately pathogenic to one species and not pathogenic at all to another species. Previous work has shown that an exotic species of lady beetle is not susceptible to this fungus. Thus, the susceptibility of the natives and the resistance of the exotic may allow for the exotic to compete with native lady beetle species.

Technical Abstract: In this study we determined the differential susceptibility of four native North American Coccinellidae (Coleomegilla maculata, Cycloneda munda, Olla v-nigrum and Hippodamia convergens) to different isolates of the insect-pathogenic fungus Beauveria bassiana. These species are all known to overlap within the same habitats. The strains/isolates of this fungus were derived from 1) a commercial product (GHA strain), 2) Isolate ‘B’ derived from a naturally-infected O. v-nigrum adult and 3) the BbAR1 strain derived from soil in a pecan orchard and were selected based upon: 1) the wide-range of susceptible insects, i.e, GHA, 2) the known susceptibility of a native species, i.e, Isolate B, and 3) the unknown virulence of B. bassiana, i.e., BbAR1, from a habitat that encompassed all native species tested yet was distant to the area from which Isolate B was collected. Additionally, in one assay, we included two species of exotic coccinellids, H. axyridis and C. septempunctata, which have successfully established in North America. We found that differential susceptibility to B. bassiana exists among native lady beetles. Moreover, we have shown that different sources of inoculum result in differential rates of mortality among the native beetles. Isolate B consistently resulted in the highest mortality. Mortality of all species treated with GHA and BbAR1 was similar to control mortality. Higher mortality of O. v-nigrum and C. munda when treated with Isolate B showed that these two native species are quite susceptible to this isolate. The native C. maculata was resistant to all B. bassiana treatments applied, as were the exotic C. septempunctata and H. axyridis. Of the native species tested, it appears that the more-susceptible O. v-nigrum and C. munda would likely face higher levels of interspecific competition with invading competitors such as H. axyridis. These native species, and possibly others, must confront both the higher rates of infection and interspecific competition from the invading species, whereas a native species such as C. maculata is relatively immune to the pathogen.