Keywords: 
• abamectin /
• Apis mellifera L. /
• acute oral toxicity /
• chronic oral toxicity /
• sub-lethal effect

Abstract: The in vivo oral toxicity of abamectin on honeybees were studied here via oral feeding, with either a single-dose of high concentration abamectin to determine the acute effects, or regular feedings at sub-lethal levels for the chronic effects. The results showed that the acute dose was 0.00700 μg a.i.·bee^-1 (48 h-LD₅₀), while the chronic dose was 0.000308 μg a.i.·bee^-1·d^-1 (240 h-LDD₅₀). In the sub-lethal cases, the subjects of two groups (0.0233 mg a.i.·L^-1 and 0.0467 mg a.i.·L^-1) developed significantly-decreased food intake after 168 h, suggesting that abamectin poisoning had severely impaired their foraging ability. Besides, the toxic effects remained prominent even in groups being mildly treated but regularly exposed to abamectin of 0.0467 mg a.i.·L^-1, and the subjects had lost 54.86% of their weights after the trial. The crawling ability of honeybees was another indicator employed to evaluate the toxicity, and all treatment groups exhibited lower passing rates than that of the control, especially for groups of 0.0117, 0.0233 and 0.0467 mg a.i.·L^-1 (P<0.05). In conclusion, oral abamectin was highly toxic to honeybees, and acute poisoning resulting from high-dose exposure normally led to instant death. Long-term exposure to abamectin at sub-lethal levels on the other hand, would significantly jeopardize the physical conditions by compromising the athletic abilities including foraging, crawling and flying, all of which together with weight loss eventually caused a high mortality rate. Therefore, the spraying of such pesticide is supposed to be kept away from the honeybee habitats, as well as entomophilous flowers during their florescence.