Insecticidal activity and underlying molecular mechanisms of a phytochemical plumbagin against Spodoptera frugiperda

Plumbagin is an important phytochemical and has been reported to exhibit potent larvicidal activity against several insect pests, However, the insecticidal mechanism of plumbagin against pests is still poorly understood. This study aimed to investigate the insecticidal activities of plumbagin and the underlying molecular mechanisms against a devastating agricultural pest, the fall armyworm . The effects of plumbagin on larval development and the activities of two detoxification enzymes were initially examined. Next, transcriptomic changes in after plumbagin treatment were investigated. Furthermore, RNA-seq results were validated by qPCR. Plumbagin exhibited a high larvicidal activity against the second and third instar larvae of with 72 h LC of 0.573 and 2.676 mg/g, respectively. The activities of the two detoxification enzymes carboxylesterase and P450 were significantly increased after 1.5 mg/g plumbagin treatment. Furthermore, RNA-seq analysis provided a comprehensive overview of complex transcriptomic changes in larvae in response to 1.5 mg/g plumbagin exposure, and revealed that plumbagin treatment led to aberrant expression of a large number of genes related to nutrient and energy metabolism, humoral immune response, insect cuticle protein, chitin-binding proteins, chitin synthesis and degradation, insect hormone, and xenobiotic detoxification. The qPCR results further validated the reproducibility and reliability of the transcriptomic data. Our findings provide a valuable insight into understanding the insecticidal mechanism of the phytochemical plumbagin.