Insecticides used for controlling cotton mealybug pose a threat to non-target bumble bees

Bumble bees (Bombus spp., Hymenoptera, Apidae) play a crucial role in pollinating greenhouse tomato crops. However, tomato production is constantly threatened by different invasive pests that often lead to the increased use of pesticides, with negative consequences for pollinators. The cotton mealybug Phenacoccus solenopsis has recently been reported in Mediterranean tomatoes and its chemical control raises concerns also regarding bumble bees. In the laboratory, we evaluated the acute toxicity and sublethal effects in B. terrestris workers exposed to the diet contaminated with four insecticides (acetamiprid, pyriproxyfen, sulfoxaflor, and thiamethoxam), potentially used to control P. solenopsis. Sulfoxaflor and thiamethoxam significantly reduced the survival of B. terrestris, while acetamiprid and pyriproxyfen altered its feeding behaviour, and the bumble bees were unable to detect the contaminated solution. Moreover, neurotoxic symptoms were observed in bees exposed to acetamiprid and alterations of the midgut were detected in bees exposed to both acetamiprid and pyriproxyfen. These results show that insecticides with low levels of toxicity to bumble bees (e.g. acetamiprid and pyriproxyfen), can cause sublethal effects on them, increasing concern about the use of these substances. Our findings provide valuable insights as regards optimizing bumble bee pollination services with chemical pest control within the context of Integrated Pest and Pollinator Management.