The Effect of Temperature on the Toxicity of Insecticides against Musca domestica L.: Implications for the Effective Management of Diarrhea

BACKGROUND Diarrhea is an important cause of childhood mortality in developing countries like Pakistan because of unhygienic conditions, lack of awareness, and unwise use of preventive measures. Mechanical transmission of diarrheal pathogens by house flies, Musca domestica, is believed as the most effective route of diarrhea transmission. Although the use of insecticides as a preventive measure is common worldwide for the management of house flies, success of the measure could be compromised by the prevailing environmental temperature since it significantly affects toxicity of insecticides and thus their efficacy. Peaks of the house fly density and diarrheal cases are usually coincided and season specific, yet little is known about the season specific use of insecticides. METHODOLOGY/PRINCIPAL FINDINGS To determine the temperature-toxicity relationship in house flies, the effect of post-bioassays temperature (range, 20-34°C) on the toxicity of seven insecticides from organophosphate (chlorpyrifos, profenofos), pyrethroid (cypermethrin, deltamethrin) and new chemical (emamectin benzoate, fipronil, spinosad) classes was evaluated by using a feeding bioassay method. From 20-34°C, the toxicities of chlorpyrifos, profenofos, emamectin and fipronil increased 2.10, 2.93, 2.40 and 3.82 fold (i.e. positive temperature coefficient), respectively. Whereas, the toxicities of cypermethrin, deltamethrin and spinosad decreased 2.21, 2.42 and 3.16 fold (i.e. negative temperature coefficient), respectively. CONCLUSION/SIGNIFICANCE These findings suggest that for the reduction in diarrheal cases, house flies should be controlled with insecticides according to the prevailing environmental temperature. Insecticides with a positive temperature coefficient may serve as potential candidates in controlling house flies and diarrhea epidemics in hot season and vice versa.