Exposure of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) Females to Spinosad: Effect on the Fitness of Their Progeny

The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a widespread pest of stored products. While the direct effects of several pesticides have been evaluated on this notorious species, little is known on their indirect effects in terms of progeny fitness. In this study, we investigated the cost of different exposure intervals of T. castaneum females to spinosad by calculating the life table parameters of the progeny. For this purpose, females of T. castaneum were exposed for 5, 10 and 20 min to spinosad and progeny birth or death rates were estimated, while water was used as a control treatment. The mean values of the net reproductive rate, the intrinsic rate of increase, the finite rate of increase, the mean generation time and the doubling time of the control treatment were 6.3 females/female, 0.029 females/female/day, 1.029, 63.6 days and 24.1 days, respectively, which are indicative of the potential population increase of T. castaneum. When female parental time exposure to spinosad was 5, 10 and 20 min, the corresponding values were 0.073, 0.135 and 0.097 females/female; -0.045, -0.031 and -0.048 females/female/day; 0.956, 0.970 and 0.953; 60.6, 67.7; and 50.3 days; -15.9, -23.3 and -14.8 days, respectively, which indicate a population decrease. However, based on the 95% confidence intervals criterion, the different exposure intervals of T. castaneum females to spinosad did not affect the fitness of their progeny. These results may have bearing on the management of T. castaneum in storage facilities.