Abstract: Twenty-five pesticides, which were commonly used in the period of flowering of 4 main nectar plants in Zhejiang province, were chosen to determine the acute toxicity to bees (Apis mellifera L.) combining with the field maximum dose. The results showed that: the 48 h LC50 values of 1.8% EC abamectin to Apis mellifera L. was 0.0528 (0.0462－0.0603) mg·L-1, belongs to very high toxic grade; the 48 h LC50 values range of 1% EC emamectin benzoate, 40% EC methidathion, 10% AS nitenpyram, 40% EC phoxim, 2.5% EC lambda-cyhalothrin, 4.5% EC beta\|cypermethrin, 480 g·L-1 EC chlorpyrifos, 45% EC malathion, 10% WP imidacloprid and 90% TC trichlorfon to Apis mellifera L. were 1.02 (0.869－1.14) mg·L-1 to 13.9 (12.4－15.5) mg·L-1, belongs to high toxic grade; the 48 h LC50 values range of 15% EC pyridaben, 20% SP acetamiprid and 15% WP ethylicin to Apis mellifera L. were 43.3(37.5－50.0) mg·L-1 to 163(127－210) mg·L-1, belongs to moderate toxic grade; the LC50 values of 5% SC fenpyroximate, 250 g·L-1 EC prochloraz, 25% WP diflubenzuron, 40% EC propargite, 50% WP cyromazine, 50% WG dimethomorph, 75% WG carbendazim, 25% WP buprofezin, 35% SC procymidone, 50% WP iprodione and 75% WP chlorothalonil to Apis mellifera L. were higher than 200 mg·L-1, belongs to low toxic grade. The results showed that 1.8% EC abamectin, 1% EC emamectin benzoate, 40% EC methidathion, 10% AS nitenpyram, 40% EC phoxim, 2.5% EC lambda\|cyhalothrin, 4.5% EC beta\|cypermethrin, 480 g·L-1 EC chlorpyrifos, 45% EC malathion and 90% TC trichlorfon had very high risk to Apis mellifera L. 10% WP imidacloprid, 15% EC pyridaben and 5% SC fenpyroximate had high risk to Apis mellifera L. 20% SP acetamiprid, 15% WP ethylicin, 250 g·L-1 EC prochloraz, 40% EC propargite, 50% WP cyromazine and 50% WG dimethomorph were moderately risk to Apis mellifera L., while other pesticides were low-risk to Apis mellifera L．

Key words: nectar plant, pesticide, Apis mellifera L., toxicity, risk assessment