Acute toxicity and first tier risk assessment of four neonicotinoid insecticides to honeybees

The acute toxicities of 4 neonicotinoid insecticides (technical materials and formulations) including imidacloprid, thiamethoxam, clothianidin and acetamiprid to Apis mellifera adult worker honey bees were determined by ‘oral-feeding tube’ and topical application methods, and the first tier risk assessment was carried out by using a parameter of hazard quotients (HQ).The results showed that the oral toxicity 48 h-LD50 values of 97.3% imidacloprid technical, 25% imidacloprid WP, 96% thiamethoxam technical, 30% thiamethoxam SC, 97% clothianidin technical, 5% clothianidin WP, 96% acetamiprid technical, 40% acetamiprid SP to honeybees were 8.04×10-3, 9.46×10-3, 7.04×10-3, 4.64×10-3, 11.8×10-3, 5.25×10-3, 5.22, 6.31 μ g a.i./bee, respectively, and the acute contact toxicity 48 h-LD50 values were 2.46×10-2, 1.33×10-2, 3.63×10-2, 9.27×10-3, 1.52×10-2, 2.21×10-2, 5.82, 5.07 μ g a.i./bee, respectively. According to the toxicity criteria of 'Test Guidelines on Environmental Safety Assessment for Chemical Pesticides', acetamiprid technical and acetamiprid SP had moderate acute toxicity, while the other 6 insecticides tested had high acute toxicity to honeybees. According to the HQ values the risk of acetamiprid to honeybees could be considered as low, while that of thiamethoxam, clothianidin and imidacloprid were high.