Toxicity of Three Commonly Used Nicotinoids and Spinosad to Apis mellifera L. (Hymenoptera: Apidae) Using Surface Residual Bioassays.

The current investigations were carried out to check the acute contact toxicity of commercial formulated insecticides viz., imidacloprid, acetamaprid, thiamethoxam and spinosad against workers of Apis mellifera L. under laboratory conditions due to their large scale application against different insect pests of crops in Pakistan. Each insecticide was evaluated at four different concentrations. The mortality of honeybees was counted after 3, 6, 12 and 24 hrs post exposure. The median lethal concentration (LC₅₀) of each insecticide was determined for Apis mellifera L. The toxicity of insecticides increased with increase in concentration and exposure time to honeybees. The results obtained were statistically highly significant and indicate that spinosad and imidacloprid were most toxic with LC₅₀ values of 13.5 and 16.6 ppm after 24 hrs post exposure to honeybees. When these results were adjusted to their commercial formulated field dose applications, they were likely to be causing potential impact to honeybees at their maximum recommended dose except acetamaprid. [ABSTRACT FROM AUTHOR]