Soil type regulates the development and insecticide susceptibility of Spodoptera frugiperda by modulating maize...

The fall armyworm, Spodoptera frugiperda, is a globally significant invasive agricultural pest. Soil type is a key environmental factor. However, how soil affects the development and insecticide sensitivity of this pest through the host plant remains unclear. This study investigated maize growth and nutritional status under three soil types (latosolic red soil, cinnamon soil, and black soil) and assessed the corresponding effects on the development and insecticide sensitivity of S. frugiperda feeding on the maize. Results showed that, compared to maize grown in relatively infertile latosolic red soil, cultivation in cinnamon or black soil significantly enhanced maize biomass accumulation and leaf nutrient levels. Larvae reared on maize from cinnamon or black soil exhibited significantly higher survival rates and improved food digestibility, alongside prolonged larval development but shorter adult longevity, compared to those fed on latosolic red soil maize. Furthermore, larval body weight increased substantially (by 37.34-54.92% at the 4th instar), while susceptibility to lambda-cyhalothrin decreased, evidenced by 1.64-1.97 times higher LC₅₀ values. Regression analysis indicated a significant positive correlation between LC₅₀ and larval weight (p = 0.014, R² = 0.99). Structural Equation Modeling (SEM) confirmed an indirect effect of soil on LC₅₀ (indirect effect = 0.834). Random Forest modeling and amino acid supplementation experiments further identified leucine and valine as the key nutritional factors mediating these effects. This study reveals the complex soil-pest-insecticide susceptibility relationship and underscores the importance of integrating soil properties into integrated pest management. The findings provide a scientific basis for developing precise and quantitative pest control strategies tailored to specific field soil conditions.