Assessing the relative attractiveness of Flupyradifurone, Acetamiprid, and Sulfoxaflor for bumblebees (Bombus terrestris) under low- and high-temperature conditions.

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Insect pollinators, including bumblebees, are declining due to multiple stressors, among which climate change and insecticide exposure interact in complex ways. While older neonicotinoids such as Imidacloprid and Thiamethoxam have been restricted, insecticides such as Flupyradifurone, Acetamiprid, and Sulfoxaflor are increasingly used as replacements. Yet, their attractiveness to bees under different thermal conditions remains poorly understood. This study aimed to assess whether these three insecticides provoke preferences or avoidance in workers of the bumblebee (Bombus terrestris) and whether such effects are modified by temperature (24 °C vs 34 °C) and concentration (minimum, low field-realistic, high field-realistic). Using a 24-h laboratory choice test with individual bees, consumption was analyzed, and bees avoided Flupyradifurone at the low concentration at 34 °C, but showed a stepwise behavioral response from avoidance to no significant difference to attractiveness with increasing concentration at high temperatures (34 °C). Acetamiprid was consistently avoided at the minimum concentration at both temperatures. Sulfoxaflor exhibited no overall insecticide-temperature effect, but the low concentration attracted bees at 34 °C. Temperature-dependent consumption patterns were also observed in the total intake of each compound; Flupyradifurone at the minimum concentration was consumed more at 24°C than at 34°C. However, at 34°C, Flupyradifurone consumption increased with concentration, compared to the minimum concentration. Acetamiprid at the low concentration was consumed more at 24°C than at 34°C; however, at 34°C, the high concentration of Acetamiprid was consumed more. The Sulfoxaflor treatment-temperature interaction had no significant effect. Similarly, the other insecticides (Imidacloprid and Thiamethoxam) showed no significant insecticide-temperature interaction effect. These results demonstrate that the relative attractiveness of these insecticides to bumblebees is temperature- and concentration-dependent. Current single-temperature risk assessments, which are also mostly conducted at room temperature, are therefore insufficient. Instead, regulatory frameworks for insecticides should incorporate multiple temperature scenarios to protect pollinators adequately.

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