Malathion resistance increases male reproductive success in Tribolium castaneum (Coleoptera : Tenebrionidae)

Malathion-specific resistance in the red flour beetle, Tribolium castaneum, is widespread and stable even in the absence of pesticide exposure. In ord er to understand this stability, both malathion resistant and susceptible m ales were placed, without pesticide, in competition but were given equal ac cess to susceptible females. Females were then isolated and their progeny w as tested for malathion susceptibility. In most cases, malathion resistance was present at a greater rate than expected. The results suggest that, in T. castaneum, selection for malathion resistance is not trade against male reproductive success. This phenomenon could explain the maintenance of mala thion-specific resistance in field populations of this stored product insec t.