Toxicological assessment of cyfluthrin, atrazine, and prothioconazole: LD50 determination in European bumblebee, <i>Bombus terrestris</i> (Hymenoptera: Apidae)

Bumblebees are efficient pollinators of fruits and vegetables in greenhouses and field crops. However, pesticide use in agricultural landscapes is causing a sharp decline in pollinating insect populations. The impact of pesticides on bumblebee health is a growing concern. Cyfluthrin, atrazine, and prothioconazole are 3 commonly used pesticides in agricultural production. Although the Food and Agriculture Organization of the United Nations has published the acute median lethal dose (LD50) data for these 3 pesticides on Apis mellifera honey bee, there is still a lack of LD50 data for non-Apis bees, such as Bombus terrestris (Linnaeus, 1758). Therefore, this study determined the oral median lethal dose (LD50) of 3 pesticides, cyfluthrin, atrazine, and prothioconazole, in European bumblebees (Bombus terrestris). The active ingredient of each pesticide was first dissolved in dimethyl sulfoxide and then diluted in a sucrose solution to prepare the pesticide-sucrose mixture for feeding. The oral LD50 values of cyfluthrin for worker bees were 4.27, 3.36, and 2.16 μg/bee at 24, 48, and 72 h, respectively. The 24-h LD50 for virgin queens was 13.49 μg/bee. For 24-h exposures in worker bees, the oral LD50 values of atrazine, prothioconazole, and their mixture were 355.3, 530.0, and 480.4 μg/bee, respectively. Pesticide-sucrose solution intake decreased as pesticide concentration increased. This study provides a preliminary evaluation of the toxicity of 3 pesticide types on bumblebees and offers insight for improving the conservation and sustainability of pollinators in agriculture. Additionally, the findings contribute to regulatory assessments by providing crucial data on pesticide effects on B. terrestris, supporting more comprehensive and effective pesticide regulations.