The effects of azadirachtin on the parasitic mite, Varroa jacobsoni and its host honey bee (Apis mellifera)

Abstract

SUMMARYWe conducted a series of experiments under laboratory conditions to evaluate the feasibility of using a neem-based (Azadirachta indica) insecticide to control varroa (Varroa jacobsoni). The experiments included studies of anti-feeding effects of azadirachtin, the active ingredient of neem-based insecticides, on adult worker honey bees (Apis mellifera); toxicity of azadirachtin to adult workers, worker larvae and associated mites; and the effects of azadirachtin on female V. jacobsoni reproduction. Both commercially formulated and purified azadirachtin were used in the experiments. The results of adult feeding experiments showed that azadirachtin significantly reduced syrup consumption by worker bees (P < 0.05) and exhibited a dose response in mortality: with an oral LC50 of 10.87 μg/ml in mite-free bees, 13.69 μg/ml in mite-infested bees, and 41.87 μg/ml for associated mites. The topical LC50 of azadirachtin was 12.53 μg/ml in mite-free bees, 12.31 μg/ml in mite-infested bees, and 35.43 μg/ml in the associated mites. The results of larval feeding experiments showed that worker larvae were more sensitive to azadirachtin than adult worker bees: exhibiting an LC50 of 180.92 μg/ml to purified azadirachtin and 100.13 μg/ml to formulated azadirachtin. More than 90% of treated, normal-appearing, white prepupae and pupae showed precocious and abnormal pigmentation on their mouthparts and other appendages. LC50‘s of topical applications of formulated azadirachtin were 104.91, 99.12 and 171.37 μg/ml for mite-free worker larvae, mite-inoculated larvae and associated mites, respectively. In addition, feeding host larvae with azadirachtin significantly reduced the fecundity of mother mites (P < 0.001) as well as egg hatching rate (P < 0.001). However, more research is needed to evaluate the reproductive effects of azadirachtin on drones, queens, and varroa under hive conditions.