Toxic Effects of Vanillic Acid and Sinapic Acid on Spodoptera frugiperda

The tolerance of the fall armyworm (Spodoptera frugiperda) to plant-derived secondary compounds gradually increases with instars. Therefore, even if plant-based additives are applied at early stages, such as the second or third instar, they may have a differential impact on the ecofriendly control of S. frugiperda. In this study, S. frugiperda larvae were exposed to vanillic acid or sinapic acid at the second and third instar, and physiological and growth parameters were measured. The results showed that the effects of vanillic acid treatment on S. frugiperda were similar at the different instars. They can significantly affect the larval carboxylesterase, glutathione S-transferase, and mixed-function oxidase activities. By reducing larval food intake, food conversion, and utilization efficiency while increasing the food consumption rate, it inhibits weight accumulation. This leads to a significant extension of the development of both the larval and pupal stages, and the adult longevity was reduced. Treatment with sinapic acid at the second instar extended the negative effects on the pupal duration of S. frugiperda when compared to treatment at the third instar, but did not affect adult longevity. Therefore, vanillic acid treatment at the second or third instar stage, can play an important role in the ecofriendly control process of S. frugiperda. The results of this study are of great significance for integrated pest management.