The following was presented at the 2010 American Bee Research Conference in Orlando, FL.

17. Johnsonc, R., L. Petersc, B. Siegfriedd & M.D. Ellisc – DRUG INTERACTIONS BETWEEN IN-HIVE MITICIDES AND FUNGICIDES IN HONEY BEES - Beekeepers must often resort to using varroacides to reduce parasitic varroa mite populations in honey bee colonies. The utility of varroacides depends on honey bee tolerance of these pesticides at dosages that kill varroa mites. Honey bee tolerance of three commonly used varroacides – coumaphos (Checkmite+TM), fenpyroximate (Hivastan TM) and tau-fluvalinate (Apistan TM) – appears to be due to bees' capacity to detoxify these pesticides through cytochrome P450 monooxygenase activity.

However, a bee’s capacity for detoxification appears to be compromised when exposed to multiple varroacides simultaneously – a likely situation given the high levels of varroacide contamination reported in beeswax. Bees treated with a sublethal dose of coumaphos were 14 times more susceptible to tau-fluvalinate, as measured by the change in LD50. Similarly bees exposed to sublethal doses of fenpyroximate were 7.6 and 5.6 times more susceptible to coumaphos and tau-fluvalinate, respectively. Bees are also frequently exposed to fungicides applied to crops since fungicides are commonly considered safe for bees and there are few restrictions on their application during bloom. However, some fungicides may affect a bee’s ability to tolerate other pesticides, including varroacides. Honey bees pre-treated with pyraclostrobin and boscalid (both components of Pristine TM) or chlorothalonil (Bravo TM) were not more susceptible to any varroacides tested. Pre-treatment of bees with the fungicide prochloraz, however, increased the toxicity of coumaphos (72 times), fenpyroximate (23 times) and tau-fluvalinate (1118 times). These results confirm earlier work demonstrating that ergosterol biosynthesis inhibiting fungicides, a class of fungicides that includes prochloraz, can inhibit cytochrome P450-mediated detoxification of pesticides in honey bees. Based on these laboratory findings, it may be prudent for beekeepers to avoid repeated use of P450-interacting varroacides – tau-fluvalinate, coumaphos and fenpyroximate – and to avoid using these varroacides when bees are likely to come into contact with P450-inhibiting ergosterol biosynthesis inhibiting fungicides.

More presentations from this conference can be found at Proceedings of the American Bee Research Conference 2010

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