Toxic evaluation of Proclaim Fit® on adult and larval worker honey bees

Impacts to honey bees due to exposure to agricultural pesticides is one of the most serious threats to the beekeeping industry. Our research evaluated toxicity of the formulated insecticides Lufenuron+Emamectin benzoate (Proclaim Fit (R)) on the European honey bee Apis mellifera L. at field-realistic concentration (worst-case scenario). Newly emerged (<= 24-h old) and forager (unknown age) worker bees were treated with the field recommended concentration of Proclaim Fit (R) using three routes of exposure including residual contact, oral, and spray within the laboratory. We also assessed the effects of Proclaim Fit (R) on the specific activity of some well-known detoxifying enzymes including alpha-esterase, beta-esterase, and Glutathione S-transferase (GST) in the honey bees. In addition, toxicity of the formulation was tested on 4th instar larvae within the hive. Based on estimated median survival times (MSTs), Proclaim Fit (R) was highly toxic to the bees, especially when applied as spray. According to our estimated relative median potency (RMP) values, newly emerged bees were 1.72x more susceptible than foragers to Proclaim Fit (R) applied orally. Enzyme assays revealed the considerable involvement of the enzymes, especially GST and alpha-esterase, in detoxification of the Proclaim Fit (R), but their activities were significantly influenced by route of exposure and age of bee. Notably, Proclaim Fit (R) was highly toxic to 4th instar honey bee larvae. Our results generally indicate a potent toxicity of Proclaim Fit (R) toward honey bees. Therefore, its application requires serious consideration and adherence to strict guidelines, especially during the flowering time of crops.