Herbivore-Induced Maize Volatiles Override Feeding Behavior and Elicit Antifeedant Responses in Spodoptera frugiperda

The fall armyworm [Spodoptera frugiperda (J. E. Smith)] is an invasive pest of maize, posing significant threats to crop productivity. While herbivore-induced plant volatiles (HIPVs) play a central role in indirect plant defenses, the contribution of hydrocarbon-based volatile organic compounds to S. frugiperda resistance remains underexplored. This study investigated the VOC profiles of maize seedlings infested by S. frugiperda compared to uninfested controls, and evaluated the bioactivity of selected synthetic VOCs on larval feeding performance. GC-MS analysis revealed qualitative and quantitative shifts in the maize volatilome following herbivory, with 11 VOCs-including mesitylene, cyclohexane, hexadecane, and eicosane-uniquely induced in infested plants. Hydrocarbon compounds dominated the altered profiles, suggesting their potential defensive function. To validate their bioactivity, nine synthetic hydrocarbons were applied to semi-synthetic diets, and their effects on larval development, feeding, and nutritional indices were assessed. Among them, eicosane and cyclohexane exhibited the strongest suppressive effects, significantly reducing larval weight gain, food intake, frass production, relative growth rate (RGR), relative consumption rate (RCR), and approximate digestibility (AD). Octane and pentatriacontane showed moderate inhibitory effects, while tetracosane and henicosane were largely ineffective. The results demonstrate that specific hydrocarbon-based VOCs not only correlate with herbivore attack but also directly impair pest growth and digestion. This study underscores the functional importance of herbivory-induced hydrocarbons in maize defense and identifies promising VOCs for development as biocompatible agents in sustainable pest management strategies.