Fitness costs of sublethal exposure toBacillus thuringiensisinHelicoverpa armigera: a carryover study on offspring

Abstract

AbstractBacillus thuringiensis(Bt) is an efficient entomopathogen used for pest control. WhileBt pathogenesis has been thoroughly studied, less is known about the biological effects of sublethalBt exposure. To address this knowledge gap, we document sublethal effects ofBacillus thuringiensisvar.kurstaki(Btk) on the biology and development ofHelicoverpa armigera(Hübner) under laboratory conditions. The results obtained revealed that duration of the different life stages in treated neonates ofH. armigerawas significantly affected by sublethal treatments. Furthermore, fecundity was also negatively affected in female moths developed fromBtk‐treated neonates, with the rate of egg hatchability reaching zero in theLC25. We also present data supporting that the effect of sublethalBtk concentrations could carry over to the next generation. SublethalBtk concentrations reduced the net reproduction rate (R0), 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 (rmandλ, respectively) were significantly lower in insects treated with sublethalBtk concentrations compared with control insects. Consequent with the reduce rate of development observed forH. armigeratreated withBtk, the mean generation time (T) and doubling time (DT) were significantly higher in insects exposed to anyBtk concentration tested compared with control. Our data demonstrate significant fitness costs resulting from sublethalBtk exposure inH. armigera. These observations underline the importance of considering the role of sublethal effects when attempting to evaluate the impact ofBt treatment on an insect pest population and its progeny.