Combination Effects Of Six Pesticides On Honey Bees (Apis Mellifera Ligustica)

Pesticides play an important role in the control of agricultural pests,but they also have toxic effects on non-target insects such as honey bees.In agricultural production,several pesticides are often applied at the same time.However,there are few research on the synergistic effects of these pesticides on bee toxicity.Therefore we through evaluated the six kinds of pesticides;thiamethoxam（Th）,imidacloprid（Im）,clothianidin（Cl）,lambda-cyhalothrin（λ-cy）,beta-cypermethrin（β-cy）and abamectin（Ab）on honey bees survival and physiological combination effects.The acute toxicity of six pesticides to honey bees was tested by“oral-feeling tube”method;While the mortalities,acetylcholinesterase（ACh E）and glutathione S-transferase（GSTs）activities of honey bees was measure at 48 h after the bees were exposed to LD₁₀ of thiamethoxam,imidacloprid and clothianidin,and binary mixtures of these pesticides.Finally,we used a binary mixture treatment of pesticides for honey bees,in which LD₁₀ dose of thiamethoxam was mixed with three other pesticides:lambda-cyhalothrin,beta-cypermethrin and abamectin,the mortality rate was statistics and the activities of acetylcholinesterase,glutathione S-transferase,polyphenol oxidase（PPO）and alkaline phosphatase（ALP）were assay,and the relative expression level of enzyme gene was elevated.The main results are as follows.1.Acute toxicity of six pesticides to honey beesIn this study,six pesticides including thiamethoxam,imidacloprid,clothianidin,lambda-cyhalothrin,beta-cypermethrin and abamectin were selected.The acute oral toxicity of these 6 pesticides to honey bees was detected by feeding tube method.The LD₅₀ values for the honey bees were（ng/bee）:Th:9.02,Im:19.091,Cl:9.107,λ-cy:854.63,β-cy:277.281 and Ab:0.791,and the LD₁₀ values were（ng/bee）Th:3.002,Im:5.0698,Cl:3.734,λ-cy:264.468,β-cy:104.260,and Ab:0.326.According to the guidelines for the testing of chemicals:Honey bees,acute oral toxicity test,thiamethoxam,clothianidin and abamectin are highly toxic to bees,while imidacloprid,λ-cyhalothrin andβ-cypermethrin are highly toxic to honey bees.2.Combination effects of three neonicotinoid pesticides on honey beesThe mortalities were significantly increased by binary mixtures of three pesticides（P<0.05）.The synergistic effect of Th+Im and Th+Cl could increase the toxicity to bees（Q>1.15）.The activities of ACh E in pesticide treatment groups were all significantly higher than control（P<0.05）.Binary mixtures of Th+Im and Th+Cl could significantly increased the activities of ACh E（P<0.05）.The activities of GSTs were distinctly inhibited by the mixture of Th+Cl（P<0.05）;however,there were no significant differences in the activities of GSTs in other pesticide groups.Combined toxicity was detected from mixtures of Th+Im and Th+Cl showed synergistic interaction.Binary mixtures of neonicotinoids showed different physiology changes than single neonicotinoids in honey bees.3.Combination effects of thiamethoxam alone and binary mixtures with three widelyused pesticides on honey beesWe used a binary mixture treatment of pesticides for honey bees,in which a sub-lethal dose of thiamethoxam was mixed with three other common pesticides:λ-cyhalothrin,β-cypermethrin and abamectin.Compared with the single pesticide use,the mortality rate differed in the group with a mixture of pesticides.The combinations of Th+λ-cy and Th+Ab had a synergistic effect（Q>1.15）on bees,and significantly higher mortality was observed in combination groups than in single treatment groups.However,the mixture of Th+β-cy had an antagonistic effect（Q<0.85）on bees,and the mortalities in these groups were almost identical.Furthermore,the mixtures of Th+λ-cy and Th+Ab significantly suppressed the activity and expression of glutathione S-transferases,which are key detoxification enzymes in insects.This result suggests that combinations of Th+λ-cy and Th+Ab of a given concentration adversely affect the survival of honey bees.