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Title: Impact of two treatments of a formulation of Beauveria bassiana (Deuteromycota: Hyphomycetes) conidia on Varroa mites (Acari: Varroidae) and on honeybee (Hymenoptera: Apidae) colony health

Author
item Meikle, William
item MERCADIER, GUY - USDA-ARS-EBCL
item HOLST, NIELS - DIAS, FLAKKEBIERG, DK
item GIROD, VINCENT - ADAPRO-LR, LATTES, FR

Submitted to: Experimental and Applied Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2008
Publication Date: 12/1/2008
Citation: Meikle, W.G., Mercadier, G., Holst, N., Girod, V. 2008. Impact of two treatments of a formulation of Beauveria bassiana (Deuteromycota: Hyphomycetes) conidia on Varroa mites (Acari: Varroidae) and on honeybee (Hymenoptera: Apidae) colony health. Experimental and Applied Acarology.vol 46, pages 105-117.

Interpretive Summary: Varroa mites are one of the most important pests of honeybees worldwide and beekeepers are very interested in new ways to treat varroa infestations without using chemicals that contaminate honey and wax. Biopesticides, which use pest diseases to control the pests, are one option, but many diseases of insects and mites are not very specific and might hurt the bees. We have already published results in which we applied a single treatment of the biopesticide and carefully measured varroa density and bee colony health. In this experiment, we applied two treatments of the biopesticide and, as in previous work, carefully measured varroa fall onto sticky boards as well as hive size and weight gain. We found no negative impact of fungus treatment on the bees, and we did find that the fungus caused more mites to fall than usual, as it should. We compared the change in the proportion of infected varroa mites and the numbers of fungal propagules per bee before and after treatment with results from other experiments. Commercial and hobby beekeepers should benefit from a new, chemical-free way to kill varroa mites.

Technical Abstract: Bee colonies in southern France were treated with conidia from 2 strains of Beauveria bassiana – one commercial (GHA) and the other isolated from Varroa mites in the region (Bb05002). Objectives were to evaluate treatment effect on colony weight, adult bee mass, capped brood, and on Varroa fall onto sticky boards. Treatments included conidia formulated with either carnauba or candelilla wax powder, candelilla wax powder alone, or control; in 2 treatment groups formulation was applied a second time after 1 week. Treatment did not affect colony health. Colonies treated twice with Bb05002 conidia and carnauba wax powder had significantly higher mite fall compared to colonies treated with blank candelilla wax powder. The proportion of fallen mites that were infected in both conidia treatments was higher than controls for 18 days after the second treatment. The number of fungal propagules on the bees themselves remained elevated for about 14 days after the second treatment. These results were compared to published results from previous experiments with regard to infection duration.