Gossypol-induced fitness gain and increased resistance to deltamethrin in beet armyworm, Spodoptera exigua (Hübner)

BACKGROUND: In plant-insect interactions, phytotoxins such as gossypol, exert a defensive role on behalf of the plant by interfering with the essential metabolic, biochemical and physiological pathways of herbivorous insects. The beet armyworm, Spodoptera exigua (Hubner), is a key pest for many important crops including a range of vegetables, ornamentals, and cotton. For this study we investigated how resistance to deltamethrin relates to enzyme activity in gossypol-pretreated larvae of S. exigua. RESULTS: Through selection with deltamethrin insecticides on gossypol-pretreated larvae for 10 generations, the Gos-SEL population developed a 113.29-fold resistance. Under the same conditions the Delta-SEL selected population showed a 69.76-fold increase resistance along with corresponding levels of xenobiotic defense enzymes activity. Similarly, the fecundity of the Delta-SEL population along with male and female longevity were found to be significantly lower when compared to the Gos-SEL population and the lab susceptible-strain group (Lab-SS). In addition, the activities of cytochrome P450s in S. exigua were significantly enhanced when the insects were fed on a deltamethrin and gossypol-pretreated diet compared with being fed on deltamethrin alone. CONCLUSION: The reproductive capacity of S. exigua is significantly reduced in the Delta-SEL and Gos-SEL populations compared to the control group (Lab-SS). Elevation of the major detoxification enzyme cytochrome P450 monooxygenase and esterase might play an important role to induce tolerance to the deltamethrin in gossypol-fed S. exigua populations. This study enhances our understanding of detoxification enzyme pathways for S. exigua gene expression and their role in responses to insecticides and plant secondary metabolites.