Effects of Sublethal Concentrations of Chlorpyrifos on Olfactory Learning and Memory Performances in Two Bee Species, Apis mellifera and Apis cerana

Chlorpyrifos is a widely used organophosphorus insecticide. The acute oral 24 h median lethal dose (LD50) value of chlorpyrifos in Apis mellifera and in Apis cerana was estimated to assess differential acute chlorpyrifos toxicity in the two bee species. The LD50 values of chlorpyrifos in A . mellifera and in A . cerana are 103.4 ng/bee and 81.8 ng/bee, respectively, which suggests A . cerana bees are slightly more sensitive than A . mellifera bees to the toxicity of chlorpyrifos. Doses half the acute LD50 of chlorpyrifos were selected to study behavioral changes in the two bee species using proboscis extension response assay. A . mellifera foragers treated with chlorpyrifos showed significantly lower response to the 10% sucrose solution compared to control bees after 2, 24 and 48 h. Chlorpyrifos significantly impaired the olfactory learning abilities and 2 h memory retention of forager bees regardless of honey bee species, which may affect the foraging success of bees exposed to chlorpyrifos.