Variation in Oral Acute Toxicity of Thiamethoxam According to the Volume Administered in Algerian Honeybees

Thiamethoxam is a neurotoxic systemic insecticide belonging to the neonicotinoid family. Approved under the trade Algeria Actara WG 25%, the plant protection product is recognized as toxic to the bees after acute exposure. However, this product is persistent, has a significant residual activity and accumulates in plants. It is therefore necessary to completely reassess its toxicity. To do this, we determined the sensitivity of the Saharan and Tellian honeybee, Apis mellifera sahariensis and Apis mellifera intermissa, to thiamethoxam by testing the acute oral toxicity on worker bees in the laboratory. The study is based on determining the LD50 according to the volume administrated. Each batch of bees was fed 100, 200, 500 and 1000μl (5, 10, 25 and 50μl per bee) 55,5% (w/v) sucrose solution with increasing doses (1, 10, 20, 50, 70 and 90 ng per bee) of thiamethoxam dissolved in acetone, for trial treatments, and 55,5% (w/v) sucrose solution supplemented with acetone, control treatments. The results showed that the toxicity is manifested by acute symptoms of early neurotoxicity and cumulative mortalities that occur 24 hours after treatment. The LD50 varies with the volume administered. Indeed, the LD50 values decrease with increasing volume, and there is an inverse relationship between the LD50 obtained and administered volumes.