Fitness costs of sublethal exposure to<i><scp>B</scp>acillus thuringiensis</i>in<i><scp>H</scp>elicoverpa armigera</i>: a carryover study on offspring

Abstract

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.