Field Attraction of Natural Enemies to Methyl Salicylate Differs Between Annual and Perennial Cropping Systems

Methyl salicylate (MeSA) is an herbivore-induced plant volatile (HIPV) known to attract natural enemies of herbivores; however, its effectiveness as a semiochemical across diverse cropping systems and broad geographic regions remains unclear. In this 2-year field study, we sampled natural enemies using MeSA-baited and unbaited (control) yellow sticky traps across multiple cropping systems in the Mid-Atlantic and Northeastern United States (New York, Pennsylvania, Virginia and New Jersey), including three annual crops (corn, potatoes, and soybean) and four perennial crops (apples, blueberries, cranberries and grapes). Sticky traps were deployed for 4 weeks during the preharvest period, with deployment timing adjusted to the phenology of each crop. For each trap, we recorded both the number of natural enemies and their community composition, including abundance and diversity (Shannon index). We found that hoverflies (Diptera: Syrphidae) were specifically attracted to MeSA in perennial cropping systems. Although natural enemy communities were overall more diverse in annual crops, MeSA tended to increase Shannon diversity in perennial systems. Collectively, these results suggest that HIPVs such as MeSA may be useful for enhancing hoverfly attraction in less-disturbed perennial cropping systems.