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Submitted to: Bulletin of Insectology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/14/2009 Publication Date: 5/12/2010 Citation: Riddick, E.W., Cottrell, T.E. 2010. Is the Prevalence and Intensity of the Ectoparasitic Fungus Hesperomyces virescens Related to the Abundance of Entomophagous Coccinellids?. Bulletin of Insectology. 63:71-78. Interpretive Summary: Lady beetles are important natural enemies of soft-bodied insects (such as aphids) in various crops during the spring and summer. A parasitic fungus was found infecting lady beetles in multiple habitats in Georgia, USA. Parasite infection increased as the relative abundance of two lady beetles (an exotic species and a native species) increased. The fungus spreads during social contact between infected and uninfected individuals. The presence of the fungal parasite may affect commercial shipment and storage of lady beetles for the biological control of pests. Technical Abstract: Hesperomyces virescens Thaxter is a laboulbenialean fungus that parasitizes certain entomophagous coccinellids in several countries. It transmits horizontally between coccinellid adults via social contact. Only recently has the exotic coccinellid Harmonia axyridis (Pallas) served as host to this parasite. We monitored the presence of H. virescens on H. axyridis and other coccinellids that share habitats. The relative abundance of coccinellids in an agroecosystem may affect the transmission dynamics of H. virescens. Therefore, we predicted that the prevalence and intensity of H. virescens would be greatest on the more abundant coccinellid species. We collected lady beetles from plant foliage in a 480 ha agroecosystem in Byron, Georgia, USA, from April through October 2007. The prevalence and intensity of the parasite was greatest on H. axyridis, which was the most abundant coccinellid collected in early spring and summer. There was a positive relationship between parasite infection of H. axyridis and the native Olla v-nigrum Mulsant; parasite infection increased as relative abundance of both species increased. The parasite was seldom on one of its original hosts, Hippodamia convergens Guérin-Méneville, and never on the exotic Coccinella septempunctata L. even though the latter species was the second most abundant coccinellid in the agroecosystem. Lack of infection of an abundant coccinellid such as C. septempunctata could result from low encounter rates and not just low susceptibility to infection. H. virescens transmission may vary depending on frequency of contact between infected and uninfected coccinellids in shared habitats. |
