Contact toxicity of deltamethrin against Rhyzopertha dominica (F.), Sitophilus oryzae (L.), and Tribolium castaneum (Herbst) adults

This study was conducted in the context of evaluating deltamethrin-treated prototype bags for efficacy against stored-product insect pests. We evaluated dose response to deltamethrin by adults of three stored-product insects, namely, Rhyzopertha dominica (F.), Sitophilous oryzae (L.), and Tribolium castaneum (Herbst) to determine the knockdown effect of deltamethrin. Knockdown in insects as a result of exposure to insecticide is defined as the state of intoxication and partial paralysis. Eight different concentrations, 1, 25, 50, 100, 250, 500, 1000, and 3000 ppm of deltamethrin over two exposure periods, 24 or 48 h, were tested. Toxicity assessments for knockdown were made at each 15 minute interval after the initial exposure and at 0.5, 1, 2, 4, 8, 12, 24, 48, and 72 h after being transferred to clean Petri dish with diet. Results show that the concentration of deltamethrin affected time to knockdown. Both, the concentration and the exposure period affected recovery of insects after transfer to diet. Insects exposed to lower concentration for 24 h recovered sooner than insects exposed to higher concentrations for 48 h. In general, at concentrations 100 ppm and higher all insects were knocked down after 2 h exposure and recovery began 4 h after transfer to diet. Results show that for all three species studied, deltamethrin has strong knockdown effect within 2 h after exposure at concentrations 100 ppm and higher. Future studies will be focused on evaluating the efficacy of deltamethrin-impregnated fabric against insects and ability of the bags to spread/contain infestation.