Submitted to: Southeastern Pecan Growers Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 20, 2003
Publication Date: June 20, 2003
Citation: Cottrell, T.E., Shapiro Ilan, D.I. 2003. Impact of an endemic entomopathogenic fungus on lady beetles in pecan orchards. Southeastern Pecan Growers Meeting Proceedings. v. 96:53-60. Interpretive Summary: Reductions in aphid populations in pecan orchards has been achieved through predation upon aphids by the recently established multicolored Asian lady beetle. Reasons for the successful establishment of this species are unknown. We discovered that a native lady beetle, Olla v-nigrum, was commonly infected with a fungal pathogen in pecan orchards; whereas, multicolored Asian lady beetle was not. Laboratory tests revealed that several collections of the fungus from the native lady beetle were not pathogenic to the exotic lady beetle. We hypothesize that the exotic ladybeetle has gained a competitive edge over the native lady beetle through disease resistance.
Technical Abstract: The exotic multicolored Asian lady beetle, Harmonia axyridis, became established and recently spread across much of North America and southern Canada. In a habitat now used by both the invading H. axyridis and a native lady beetle, Olla v-nigrum, we discovered that the native lady beetle was commonly infected by Beauveria bassiana; whereas, the exotic H. axyridis, was not. Laboratory assays revealed that B. bassiana isolates collected from naturally-infected O. v-nigrum were pathogenic to adult O. v-nigrum but not to adult H. axyridis. In contrast, the GHA strain of B. bassiana was not significantly pathogenic to O. v-nigrum nor H. axyridis. Late season field collections revealed significantly higher B. bassiana infection of O. v-nigrum than H. axyridis. Our results lead us to hypothesize that low susceptibility of H. axyridis to B. bassiana (found to infect O. v-nigrum) may provide an intraguild advantage to H. axyridis over O. v-nigrum; this may also occur with other species of native lady beetles and other endemic entomopathogens in different habitats and regions.