Abstract: 【Aim】 To determine the toxicity of plumbagin (an important plant secondary substance from Chinese medicine Plumbago zeylanica) to the 2nd instar larvae of Spodoptera frugiperda and ascertain the sublethal effect of a sublethal concentration (LC₂₅) of plumbagin on the growth, development and detoxifying enzyme activities of the F₀ and F₁ generations of S. frugiperda. 【Methods】 The toxicity of plumbagin against the 2nd instar larvae of S. frugiperda (the 2nd day after ecdysis) was determined using insecticide incorporated artificial diet bioassay. After the 2nd instar larvae were exposed to LC₂₅ (0.343 mg/g) of plumbagin, the larval duration, pupation rate, pupal duration, female and male adult longevity, and number of eggs laid per female adult of the F₀ and F₁ generations of S. frugiperda were recorded, the age-stage, two-sex life table was constructed, and the activities of three detoxifying enzymes including carboxylesterase (CarE), glutathione S-transferase (GST) and cytochrome P450 monooxygenase (CYP450) were determined at 24 h after treatment. 【Results】 The median lethal concentration (LC₅₀) and LC₂₅ values of plumbagin against the 2nd instar larvae of S. frugiperda in 7 d were 0.607 and 0.343 mg/g, respectively. For the parental generation (F₀) of S. frugiperda, LC₂₅ of plumbagin significantly decreased the pupation rate by 25.13%, significantly shortened the female and male pupal duration by 1.29 and 1.08 d, respectively, significantly decreased the number of eggs laid per female by 47%, and significantly shortened the oviposition period and adult longevity by 1.75 and 1.19 d, respectively, compared to the vehicle control (0.1% acetone). For the offspring generation (F₁) of S. frugiperda, LC₂₅ of plumbagin only significantly shortened the mean generation time (T) by 0.91 d, compared to the vehicle control. LC₂₅ of plumbagin significantly induced the activities of the three detoxifying enzymes CarE, GST and CYP450 in the 2nd instar larvae of S. frugiperda after treatment for 24 h, which were increased to 1.28-, 1.30- and 1.42-fold as high as those in the vehicle control. 【Conclusion】 LC₂₅of plumbagin had obvious adverse effects on the growth, development and fecundity of the F₀ generation of S. frugiperda, and significantly increased the activities of the three detoxifying enzymes CarE, GST and CYP450 in the 2nd instar larvae after treatment for 24 h, which will be helpful for using the plant secondary substance plumbagin as one of potent biocontrol strategies for this pest.

Key words: Spodoptera frugiperda, plumbagin, life table, sublethal effect, detoxifying enzyme