Joint Effects of Temperature and Insecticides on Mortality and Fecundity of Sitophilus oryzae (Coleoptera: Curculionidae) in Wheat and Maize

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Abstract
Sitophilus oryzae (L.) were added to maize and wheat either untreated or treated with low doses of either fenitrothion or cypermethrin. Replicates were held at 22, 25, and 30°C. Adult mortality and fecundity were recorded at weekly intervals for 3 weeks. Toxicity of fenitrothion to S. oryzae adults increased with increasing temperature on both maize and wheat, whereas toxicity of cypermethrin decreased with increasing temperature. At each temperature, with both insecticides, mortality was higher and demographic performance (lxvx) was lower on maize than on wheat. Population suppression on maize, measured as changes in rm and Ro, was positively correlated with temperature for cypermethrin. On wheat, however, population growth changed very little with temperature change. Over the dose range studied, the increased demographic performance of S. oryzae on wheat was sufficient to compensate for increased adult mortality with increasing temperature.