Sulfoxaflor reduces food intake and learning efficiency of solitary Osmia bicornis bees.

Bees in agroecosystems can be exposed to multiple pesticides, such as insecticides and fungicides, but potential sub-lethal consequences on fitness-relevant endpoints like food intake, foraging performance and learning efficiency remain poorly understood. The insecticide sulfoxaflor is used as alternative to neonicotinoid insecticides, however, its impacts alone or in combination with other pesticides on foraging and learning of solitary bees are largely unknown. We conducted experiments with solitary Osmia bicornis bees to investigate the effects of field-realistic doses of sulfoxaflor alone or in combination with the fungicide azoxystrobin on female bees' food intake in the laboratory and their learning efficiency and foraging performance on artificial flowers. We found that sulfoxaflor lowered the intake of sugar solution on average by 23.8% and interacted antagonistically with azoxystrobin. Moreover, bees exposed to sulfoxaflor learned to discriminate between rewarding and non-rewarding flower colours less efficiently. However, other aspects of foraging performance were not negatively affected by the investigated pesticides. These findings suggest that field-realistic exposure to sulfoxaflor can impair food intake and learning efficiency of O. bicornis, thereby pointing out mechanistic sub-lethal pathways that may lead to a reduced fitness and harmful consequences on population dynamics of solitary bees.