Natural occurrence of Ametadoria misella (Diptera: Tachinidae) and the granulovirus of Harrisina brillians (Lepidoptera: Zygaenidae) in California

• Author(s): Mills, D.; Mills, Nicholas; Purcell, Alexander; Stark, Diane;
• Abstract: In southern California, populations of the western grapeleaf skeletonizer, Harrisina brillians Barnes and McDunnough, appear to be maintained at low levels of abundance by the combined activity of Harrisina brillians granulovirus (HbGV) and the parasitoid Ametadoria misella (Wulp). In contrast, outbreaks of H. brillians were common in central California in the late 1970s and 1980s. We investigated field populations of H. brillians in Fresno and nearby Madera Counties from 1992 to 1995 to determine the prevalence and impact of both natural enemies. A double antibody sandwich enzyme-linked immunosorbent assay (ELISA) employing polyclonal antibodies to HbGV was developed to detect virus in field samples. The sensitivity of the ELISA was apprxeq10 ng of viral protein (equivalent to 100 ng/ml in the assay) detecting granulovirus in infected H. brillians larvae 72 h after infection. The ELISA did not cross react with the multicapsid nucleopolyhedrovirus Autographa californica MNPV at concentrations as high as 105 ng/ml, but did cross react with another granulovirus Cydia pomonella GV at concentrations 103 ng/ml. H. brillians pupae were collected from 4 vineyards. Both natural enemies were abundant at all sites, and the total mortality of host pupae ranged from 53 to 98%. Granulovirus accounted for as much as 97% mortality, whereas parasitism by A. misella ranged from 12 to 33% as estimated by marginal death rate analysis. These data indicate that both natural enemies cause significant mortality of H. brillians and that, contrary to earlier reports, A. misella is established in central California. Additionally, up to 47% of H. brillians adults eclosing from overwintering pupae tested positive for granulovirus by ELISA, indicating that host adults are an important mechanism of intergenerational and interseasonal persistence of the virus in host populations.
• Publication Date: Oct 1999
• Journal: Environmental Entomology