Spinosad affects heat tolerance and heat acclimation of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) adults

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) are serious pests of stored food. Exposure to high or low temperatures is effective in controlling these two species but accompany limitations. Spinosad, derived from bacterium Saccharopolyspora spinosa, is an effective insecticide but synergistic effect on heat- or cold-acclimated insects has not been reported. The objectives of this study were to determine if spinosad affects the mortality of T. castaneum and S. oryzae adults under temperature acclimated and unacclimated conditions. Adult insects were exposed to spinosad or water, acclimated at 35℃ and 40℃, and finally held at 45℃ for 0-30 h for T. castaneum and 0-12 h for S. oryzae. The mortality of adults at different durations was recorded and LT50 values were calculated. Exposure to spinosad before heat exposure reduced the heat tolerance of T. castaneum and S. oryzae adults. Acclimation at intermediate temperatures 35℃ and 40℃ increased the heat tolerance of both S. oryzae and T. castaneum adults. Further study is needed to determine the effect of spinosad on the heat tolerance and heat acclimation of other stored-product insect species.