Lethal aerial powdering of honey bees with neonicotinoids from fragments of maize seed coat

Losses of bees have been reported in Italy concurrent with the sowing of maize coated with neonicotinoids where pneumatic drilling machine were used. Solid particles with systemic insecticide, falling on the vegetation surrounding the sown area, were thought to poison bees foraging on contaminated nectar and pollen. However, bees fed with guttation drops and dew collected from the surrounding vegetation of sown fields showed no acute toxicity. Chemical analysis showed a relatively low content of neonicotinoid in dew and guttation. Thus, the acute poisoning of bees linked to the vegetation contaminated by seed coated fragments containing neonicotinoids was again unproven. For this reason the direct aerial powdering of bees was investigated exposing caged bees around the sown area, not in contact with vegetation. High or low toxicity emerged in different trials. The synergistic effect on bees of high humidity on toxicity of powder containing neonicotinoid was hypothesized. A clear indication that bees were killed by powdering, only if held in high humidity, emerged. Chemical analysis showed high quantities of neonicotinoid insecticide in dead bees earlier exposed to dust in the field.