Effects of imidacloprid administered in sub-lethal doses on honey bee behaviour. Laboratory tests

Under certain circumstances, the effects of imidacloprid on honey bees may not be immediately perceived. The aim of this study was to investigate if imidacloprid, provided in sub-lethal doses, could influence honey bee behaviour in the laboratory. Imidacloprid (supplied as Confidor®) was offered to bees in 50 % sucrose solution at two different concentrations (100 ppb and 500 ppb of active ingredient). Each dose was administered both as single dose and ad libitum, to three sets of 10 honey bee foragers. Bees fed with 50% sucrose solution were used as a control. Feeding occurred in holding cages in an incubator in complete darkness. After administration, in each treatment, the behaviour of the bees was recorded with an IR camera, and then analysed with “The Observer” computer program. In each treatment bees were significantly less active (in terms of mobility) than bees in the untreated control. Furthermore, in the treated bees, the communicative capacity seemed to be impaired, and this could cause a decline in the social behaviour. Nevertheless, the negative effects appeared only after a certain period of time following administration (30-60 minutes) and vanished after several hours. Imidacloprid therefore has an inhibiting, even though transitory, effect on honey bees. We assume that the period of time in which honey bee behaviour is altered could negatively affect both the individual and the entire colony.