Does ingestion of neem-contaminated diet cause mortality of honey bee larvae and foragers?

Abstract

We have tested the hypothesis that ingestion of neem-based products increases mortality of Apis mellifera foragers and larvae. For this purpose, we conducted bioassays in which bees of different ages were submitted to ingestion of different neem concentrations. Foragers were treated with two concentrations of a neem-based product (120 mg a.i./l and 480 mg a.i./l) mixed with water and sugar solution (syrup). The larvae were reared in vitro and treated with larval diet mixed with two concentrations of the product (60 mg a.i./l and 120 mg a.i./l). Neem increased mortality of treated bees, and the effects were dependent on age and product concentration. Foragers submitted to ingestion of higher neem concentration that had reduced survival rate comparing with the other treatments. Larvae were more susceptible to neem than foragers because, in both tested concentrations, all larvae died before reaching prepupa stage. We discuss the potential negative effects of neem on honey bees, and suggest methods to minimize these effects.