Effects of neem (Azadirachta indica) on honey bee workers and queens, while applied to control Varroa destructor

Abstract

The objective of this study was to determine the effect of neem (Azadirachta indica) oil on mortality and development of honey bee worker brood, queen oviposition, colony performance, and Varroa destructor mortality. As a hypothesis it was indicated that adequate concentrations of neem oil may control V. destructor without affecting bee colonies. Neem oil at concentrations of 0.33–21.1%, with 7.26–464.64 mg l−1 azadirachtin, was sprayed on bee (Apis mellifera) combs. Their effects on mortality and developmental time of the brood, worker bee response on feeding and capping the larvae, and number of eggs laid by the queen were quantified. A 21.1% oil concentration resulted in 100% egg mortality, but lower concentrations resulted in minimal egg mortality. Larvae that reached the fifth instar were capped and survived the presence of the oil, but when 21.1% was applied, their development was delayed one to two days. With concentrations of 5.3 and 10.6% (116.2 and 232.3 mg l−1 of azadirachtin, respectively), queen oviposition was not significantly different from the control, but 10.6% slightly decreased oviposition. The highest V. destructor mortality (85%) was proportional to the concentration and number of spray applications. When neem oil was applied to hives, none of the concentrations used decreased bee population, capped worker larvae or the reserves of honey and pollen. However, two queens died after one application of 5.3% and three applications of 10.6%.