Mixture of neonicotinoid and fungicide affects foraging activity of honeybees.

The use of plant protection products (PPPs) is a major factor contributing to global insect decline. We here use the honeybee (Apis mellifera) as a model to study combined effects of the last neonicotinoid in the EU (acetamiprid) and different fungicides on live-long foraging flights using radio frequency identification. The mixture of the sterol-biosynthesis-inhibiting fungicide difenoconazole and the insecticide acetamiprid significantly reduced the number of foraging trips per day compared to the control and each PPP alone, while a mixture of the insecticide with the non-sterol-biosynthesis inhibiting fungicide boscalid/dimoxystrobin did not affect behaviour. This potential synergistic effect of the fungicide/insecticide mixture supports the notion that some fungicides can enhance the effect of insecticides, which did not lead to significant changes in behaviour when applied on their own. Our results emphasize the need for more studies on the interaction of different PPPs.