Fitness costs of reproductive capacity and ovarian development in a Bt‐resistant strain of the cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract

BACKGROUND The cotton bollworm Helicoverpa armigera has developed resistance to the insecticidal Cry1Ac toxins produced by Bacillus thuringiensis (Bt) in China. To gain a better understanding of the fitness cost associated with resistance evolution, reproductive capacities and ovarian development were examined in four strains of H. armigera: a Cry1Ac‐susceptible strain (96S); a Cry1Ac‐resistant strain fed on an artificial diet with Cry1Ac toxin for 135 generations (BtR); two strains derived from BtR: a strain grown without Cry1Ac selection for 38 generations (CK1) and a strain grown for one generation without Cry1Ac selection (CK2). RESULTS Strains 96S and CK1 had similar reproductive capacity and Cry1Ac susceptibility. Compared with the 96S and CK1 strains, the fecundity and hatching rate of CK2 were respectively more than 30% and 50% lower. Moreover, the number of eggs laid by BtR was significantly lower than the number of eggs laid by 96S and CK1, but higher than the number of eggs laid by CK2. In accordance with the differences in reproductive capacity, ovarian development in CK2 and BtR was significantly delayed. CONCLUSION These results indicated that there was a fitness cost in the reproductive physiology in the resistant strains. Reversion to susceptibility to the Bt Cry‐toxin in the resistant CK1 strain was associated with an increase in reproductive capacity. © 2014 Society of Chemical Industry

Dissecting the role of Krüppel homolog 1 in the metamorphosis and female reproduction of the cotton bollworm, Helicoverpa armigera

“…To analyse the function of HaKr‐h1 in JH‐mediated vitellogenesis and oocyte maturation, Kr‐h1 RNAi experiments were performed in female adults, and then the ovarian development status and number of eggs laid were recorded. Based on the characterization of ovarian development stages described previously (Zhang et al ., ), the ovarian developmental grade was measured at 2 and 4 days after dsRNA injection. The results showed that knockdown of HaKr‐h1 significantly delayed oocyte maturation, resulting in the retardation of ovary development.…”

Pathogenicity of indigenous soil isolate of Bacillus thuringiensis to Helicoverpa armigera Hübner 1809 (Lepidoptera: Noctuidae)

“…are the most damaging and cosmopolitan pest species. These species have well-adapted different agro-ecological zones around the globe from Asia to Africa to Europe (Zhang et al 2015). They are polyphagous pests with a wide range of host plants including: cotton, maize, gram, sesame, okra, tomato, potato, and many other fruit and vegetable crops (Aggarwal et al 2006;Nagoshi et al 2011).…”

Changes in vitellogenin expression caused by nematodal and fungal infections in insects

“…This trade-off strategy is not so exceptional in insects facing various stressful situations. For example, the resistance of females of the corn earworm Helicoverpa armigera against Bacillus thuringiensis toxin Cry1Ac was accompanied by the inhibition of reproduction caused by a decrease in Vg gene expression (Zhang et al, 2014(Zhang et al, , 2015. Similarly, in females of the rice stem borer Chilo suppessalis, application of sublethal doses of the insecticide chlorantraniliprole reduced Vg mRNA expression (Huang et al, 2016).…”