Reza Talaei-Hassanloui

Abstract B acillus thuringiensis ( B t) is an efficient entomopathogen used for pest control. While B t pathogenesis has been thoroughly studied, less is known about the biological effects of sublethal B t exposure. To address this knowledge gap, we document sublethal effects of B acillus thuringiensis var. kurstaki ( B tk) on the biology and development of H elicoverpa armigera ( H übner) under laboratory conditions. The results obtained revealed that duration of the different life stages in treated neonates of H . armigera was significantly affected by sublethal treatments. Furthermore, fecundity was also negatively affected in female moths developed from B tk‐treated neonates, with the rate of egg hatchability reaching zero in the LC 25 . We also present data supporting that the effect of sublethal B tk concentrations could carry over to the next generation. Sublethal B tk concentrations reduced the net reproduction rate ( R 0 ), and there were also significant differences among the values of this parameter at all treatments tested when compared with controls. The intrinsic and finite rates of increase ( r m and λ , respectively) were significantly lower in insects treated with sublethal B tk concentrations compared with control insects. Consequent with the reduce rate of development observed for H . armigera treated with B tk, the mean generation time ( T ) and doubling time ( DT ) were significantly higher in insects exposed to any B tk concentration tested compared with control. Our data demonstrate significant fitness costs resulting from sublethal B tk exposure in H . armigera . These observations underline the importance of considering the role of sublethal effects when attempting to evaluate the impact of B t treatment on an insect pest population and its progeny.

Abstract The life table and parasitism rate of Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae), a larval parasitoid of the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae), were studied at 25 ± 1°C, 65 ± 10% RH, and a photoperiod of 16:8 (L: D) h. The data were analyzed based on the age-stage, two-sex life table theory. Because the sex ratio of offspring varies with the age of the female parent, we used only female offspring to calculate the intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate (R0), and mean generation time (T) by using the jackknife technique, the values of which were 0.18407 d-1, 1.2021 d-1, 17.94 offspring, and 15.69 d, respectively. We also calculated these parameters by using bootstrap technique. They were not significantly different from those estimated by using the jackknife technique. We included both male and female offspring in the calculation of the parasitism rate. The net parasitism rate (C0) was 42.63 aphids. Moreover, population projection showed differences between simulated population based on total offspring and female offspring. Because both the offspring sex ratio and the parasitism rate depend on female age, it is necessary to use the age-stage, two-sex life table for a correct analysis. Frequency of the net reproductive rate estimated by using bootstrap technique fit normal distribution well, whereas frequency data estimated by using jackknife technique failed the normality test. We suggest that the jackknife technique should not be used for the estimation of population parameters.