Toxicity of synthetic insecticides on Tetragonula pagdeni (Hymenoptera Apidae)

Stingless bees are important pollinators in the ecosystem and crop production in most subtropical and tropical regions of the world. However, the global decline of bee populations is a serious concern. Insecticides are considered crucial factors affecting bee survival. In this study, the acute toxicity of selected synthetic insecticides (imidacloprid, profenofos, and lambda-cyhalothrin) on a stingless bee, Tetragonula pagdeni (Schwarz) (Hymenoptera Apidae), was investigated and the LD50 and LC50 determined through topical, oral, and contact exposure under laboratory conditions. The estimated topical LD50 values for imidacloprid, lambda-cyhalothrin, and profenofos were 0.06, 0.53, and 45.39 ng active ingredient (a.i.)/bee, respectively. The corresponding estimated LD 50 values from oral bioassays were 0.66, 7.52, and 75.04 ng a.i./bee, and LC50 values for contact exposure were 48.74, 4,339.83, and 3,062.81 ng a.i./cm(2) . Overall, imidacloprid exhibited the highest toxicity among the evaluated insecticides for all routes of exposure. In addition, insecticide toxicity was higher in the topical bioassay than in oral and contact bioassays. These findings demonstrate that this stingless bee is extremely vulnerable to insecticide use. Therefore, selection of insecticides in pest control programs should consider mitigation of the risk to and detrimental effects on stingless bees.