The joint effect of temperature and insecticides upon the mortality and fecundity of Sitophilus species (Coleoptera: Curculionidae)

The joint effects of temperature and insecticides upon the demographic performance of stored products insects were investigated with reference to Sitophilus zeamais L. and Sitophilus oryzae L. The results with S. zeamais were inconclusive. The pesticides used, fenitrothion and cypermethrin, against S. oryzae exhibited a positive and negative toxicity relationship with temperature at a range of 22 to 30° C, respectively. The demographic potential of S. oryzae on maize was well suppressed by insecticide treatments. The population was decreased in number at doses of 1.0 mg kg ^-1 fenitrothion at 30°C and of 1.25 mg kg ^-1 cypermethrin at 25 and 22°C. However, the population growth of S. oryzae on wheat, where the reproductive rate was relatively high, could not completely be suppressed at all temperatures with all insecticide treatments. The results suggest that the doses applied in this experiment, i.e. 1.0 mg kg ^-1 fenitrothion and 2.5 mg kg ^-1 cypermethrin, were too low to suppress completely the population growth of S. oryzae on wheat at a range of temperature between 22 and 30°C.