Limited Transmission of the Ectoparasitic FungusHesperomyces virescensbetween Lady Beetles

Abstract

The ectoparasitic fungusHesperomyces virescensThaxter (Ascomycota: Laboulbeniales) commonly infects the invasive lady beetleHarmonia axyridis(Pallas) and several other aphidophagous lady beetles in North America and Europe. We tested the hypothesis that bodily contact between adults of different lady beetle species supports horizontal transmission ofH. virescens. We used laboratory assays to determine whetherH. axyridisorOlla v-nigrum(Mulsant) harboringH. virescens(i.e., source beetles) transmit the fungus to noninfected target beetlesH. axyridis,O. v-nigrum,Coccinella septempunctataL.,Coleomegilla maculata(De Geer), orHippodamia convergensGuerin-Meneville. Results indicate that intraspecific transmission (i.e., for the source beetlesH. axyridisandO. v-nigrum) was common but interspecific transmission (i.e., from sourceH. axyridisorO. v-nigrumto target species) was low. Interspecific transmission occurred at low rates fromH. axyridisto bothC. septempunctataandO. v-nigrumand fromO. v-nigrumto bothC. septempunctataandH. convergens. Based upon our laboratory assays of forced pairings/groupings of source and target beetles, we predict that horizontal transmission ofH. virescensbetween species of aphidophagous coccinellids is possible but likely rare.