Effects of multiple applications of a Beauveria based biopesticide on Varroa destructor (Acari: Varroidae) densities in honey bee (Hymenoptera: Apidae) colonies

Authors: Meikle, William; MERCADIER, GUY - USDA-ARS-EBCL; ANNAS, FLORIS - ADAPRO-LR, LATTES, FR; HOLST, NIELS - DIAS, FLAKKEBJERG, DK

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2009
Publication Date: 6/1/2009
Citation: Meikle, W.G., Mercadier, G., Annas, F., Holst, N. 2009. Effects of multiple applications of a Beauveria based biopesticide on Varroa destructor (Acari: Varroidae) densities in honey bee (Hymenoptera: Apidae) colonies. Journal of Apicultural Research. 48(3):220-222.

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 used a strain of fungus that we found attacking varroa mites in a commercial apiary in France, and which we have already used in previous field experiments, to make a biopesticide against the varroa mites. Instead of applying the biopesticide once to twice, we applied it three times to see if we could have a large impact on the varroa population without hurting the bees. We found that the three treatments did result in fewer mites in the treated bee hives. However, the mite population was still too high, so the treatment needs to be improved. We also saw that the treated beehives may have been affected, which means we have to carefully monitor beehives in any future experiments. We combined results here with results from previous experiments to see how three applications of biopesticide compares to just one or two applications. Commercial and hobby beekeepers should benefit from a new, chemical-free way to kill varroa mites.

Technical Abstract: A biopesticide, formulated with a strain of Beauveria bassiana isolated from varroa mites, was tested in an experiment in southern France and the results were were compared to published results from previous experiments with the same biopesticide. Bee colonies were treated either with biopesticide, with wax powder alone, or left untreated. The objective was to evaluate the efficacy of 3 successive applications of biopesticide. Response variables included mite fall onto sticky boards, proportion of mites that are infected, number of fungal colony-forming units (cfu) per adult bee, number of mites per 100 adult bees, and hive growth rate. Results were compared to previous experiments using the same biopesticide in the same area. The biopesticide applications resulted in significantly lower mite falls onto sticky boards, compared to the powder only and control groups; the decline started 7-10 days after the 3rd application. The proportion of infected mites remained high up to 4 weeks after the last application, similar to another fall experiment but unlike spring experiments. The cfu density per bee dropped less sharply after the 3rd application than after the 1st application. Formulating conidia with wax powder did not significantly affect conidium dispersal within the hive or treatment duration but did facilitate application. Phoretic mite density was not significantly different among treatments four weeks after the final application, suggesting that variables such as the number of applications and the between-application interval need to be examined. Biopesticide-treated colonies grew slower than other colonies but brood surface area was not different among treatments.