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Acute toxicity of thiamethoxam to Apis mellifera and the use of esterases as biomarkers of exposure to pesticides
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Edité par CCSD ; Apimondia Foundation -
International audience. In Brazil, as well as in other countries, the use of pesticides from the recent class of neonicotinoids surpasses those from organophosphates and pyrethroids. In this class, thiamethoxam is an insecticide used in Brazil mainly to control sucking insects in several crops such as citrus, coffee, soybean, bean and cotton. However, the honey bee Apis mellifera L., 1758, which has a great value as pollinator and is required for increasing the plant production, can be exposed to residues from treatments with neonicotinoids. Thus, this work aimed to determine the acute toxicity of thiamethoxam to the honeybee expressed as LD50. This value is then used as a reference dose to assess the sublethal effects of this pesticide on type B esterases from A. mellifera. Honey bee foragers were exposed, by contact application, to different doses of thiamethoxam and mortality was measured after 24 and 48 hours. The results show that the LD50 values at 24 and 48 hours are 11.13 ng a.i./bee (CL95% = 9.71 - 12.55; D.F. = 16 and χ2 = 10.628) and 12.67 ng a.i./bee (CL95% = 9.25 - 16.08; D.F. = 18 and χ2 = 17.506), respectively. When honeybee are exposed to sublethal doses of thiamethoxam (i.e. LD50/10 or LD50/20), acetylcholinesterase and carboxylesterase significantly decreased and represented 94% and 78% of control activity at 24 hours and 48 hours, respectively. Thus, these enzymes could be used as biomarkers of exposure to pesticides to help for a better honey bee management and to follow the environmental health
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