Effect of temperature and relative humidity on the efficacy of spinetoram against Sitophilus granarius, Sitophilus zeamais and Tribolium castaneum

Abstract

Abiotic environmental variables often have strong influence on the efficacy of insecticides that ultimately affect the success of pest management programs. In the present work, effect of two important environmental variables viz., temperature and humidity, was studied on the control efficacy of spinetoram (a spinosyn insecticide) on wheat grain against three major stored insect pests: Sitophilus granarius, S. zeamais, and Tribolium castaneum. The efficacy of spinetoram at the rate of 0.1, 0.5 and 1 ppm was assessed in six combinations of temperature (20, 25, or 30 °C) and humidity (55 or 75%) levels. Based on mortality data, spinetoram efficacy against S. granarius and S. zeamais increased with the rise in temperature, but spinetoram had a weak effect to control T. castaneum at test concentrations and abiotic conditions examined. Complete mortality of S. granarius and S. zeamais resulted at 1 ppm and 30 °C at both humidity conditions after seven days of exposure. Levels of concentrations, temperatures and their interaction had a significant effect on progeny production of S. granarius and S. zeamais. The number of individuals produced of both species decreased with the increase in concentration and decrease in bioassay temperature. In conclusion, spinetoram was found to be effective against S. granarius and S. zeamais, with its efficacy synergized with the rise in temperature.