Sex-specific median lethal dose (LD50) in bumble bee adults orally and topically exposed to two insecticides and one fungicide

Wildlife is deeply impacted by human activities. Evidence-based evaluation of the main threats is challenging as it needs to be representative of the diversity of the risk of exposure and the sensitivity of the organisms, specifically for hyper-diverse groups like insects. While bees are a diverse group of > 20,000 species, standardised eco-toxicological data for non-Apis bees species remain limited, resulting potentially in the underestimation of threats the wild bees are facing. In many cases, pesticide acute data are available for only one exposure route, most often contact median lethal dose 50% (LD50) values, and primarily focus on social workers or solitary females. In this context, we determined the contact and oral LD50 of three active ingredients of two insecticides and one fungicide, namely acetamiprid, cypermethrin and tebuconazole in males and workers of the bee model Bombus terrestris. Acetamiprid and tebuconazole were practically non-toxic under both exposure routes, whereas cypermethrin was the most toxic compound, exhibiting higher toxicity via contact exposure. Interestingly, males showed greater sensitivity than females after both oral and topical exposure to cypermethrin, and after oral exposure to acetamiprid. Our findings highlight the need for additional data on reproductives and for the identification of factors that determine their differential sensitivity.