Biological traits, detoxification enzyme activity, and transcriptomic profiles of the fall armyworm in response to nicotine

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae) (J.E. Smith), is an important polyphagous agricultural pest. It has more than 350 host plant species, and this range is steadily expanding. Notably, tobacco has gradually been accepted as its host. Nicotine is an important secondary metabolite produced by tobacco plants. In this study, S. frugiperda was exposed to nicotine to examine its effects on biological traits, detoxification enzyme activity, and transcriptomic profiles. Our results showed that seven different concentrations of nicotine significantly reduced the survival rate of FAW larvae. Nicotine at 0.01, 0.1, 0.2, and 0.4 mg/g significantly decreased the weight of S. frugiperda larvae and pupae. Exposure to nicotine significantly extended the whole developmental duration. Female fecundity was also significantly decreased. Moreover, an increase in the activities of detoxification enzymes was observed in cytochrome P450 monooxygenases, carboxylesterases, glutathione S-transferases, and mixed-function oxidases after exposure to nicotine. Transcriptomic analysis showed that the expressions of 3,632 genes were altered after exposure to nicotine. Among them, CYP6AB60P, CYP4M15, CYP301A1, CYP6AB59, CYP340K14, GST1a, and CarE-6a were significantly upregulated after exposure to nicotine by quantitative real-time PCR. These findings are instrumental in elucidating the molecular mechanisms underlying the tolerance of S. frugiperda to nicotine, and it's helpful to uncover the intricacies of the FAW's adaptability to broaden its host range.