Doses of insecticides used in pollination-dependent crops harm Apis mellifera in laboratory conditions

ABSTRACT Understanding the toxicity of insecticides on the bee Apis mellifera (Hymenoptera: Apidae) is crucial for the conservation of this vital pollinator in agricultural systems. From this perspective, the objective in this study was to evaluate the toxicity of the insecticides flupyradifurone (Butenolide) and thiacloprid (Neonicotinoid) to A. mellifera under laboratory conditions. Three commercial doses commonly used in Brazilian crops were tested for flupyradifurone (0.1, 0.15, and 0.2 g a.i. L-1) and thiacloprid (0.072, 0.12, and 0.168 g a.i. L-1), along with two controls: absolute (distilled water) and positive (thiamethoxam insecticide). The insecticides were administered via direct spray application and ingestion through a contaminated diet, and their effects on mortality, motor function disorders, and flight ability of surviving bees was evaluated. Flupyradifurone caused 100% mortality at all doses via direct spraying, with a LT50 of 2.15 hours at 0.2 g a.i. L-1, and resulted in 16.44% mortality via contaminated diet, with a LT50 of 304.56 hours. thiacloprid led to 46.33% mortality via direct spraying (LT50 = 70.28 hours), and 33.92% mortality via ingestion, with a LT50 of 304.56 hours at 0.072 g a.i. L⁻1 and 143.05 hours at higher doses. Both insecticides, regardless of dose and exposure route, impaired the flight ability of A. mellifera, causing motor dysfunction. Flupyradifurone was highly toxic to adult worker bees via direct spraying and mildly toxic via ingestion, whereas thiacloprid was slightly toxic through ingestion and caused moderate mortality when sprayed directly.