Response of predaceous arthropods to methyl salicylate in agricultural fields

Methyl salicylate (MeSA) is an herbivore-induced plant volatile that has shown potential in attracting natural enemies. In the present study we conducted a meta-analysis to evaluate the magnitude of natural enemy response to MeSA in the field, and tested its attractiveness to insect predators in commercial cranberry bogs. Eighteen experiments from 14 publications that tested the impact of MeSA on insect natural enemies in the field were used in the meta-analysis, resulting in 91 total observations. Of these, 41 documented significant attraction and the magnitude of this attraction response was not significantly different across predator and parasitoid taxa. In cranberries, the response of insect predators to MeSA was monitored weekly in 15 commercial cranberry bogs for eight consecutive weeks. All bogs contained a pair of yellow sticky traps: one baited with a MeSA lure (PredaLure) and one unbaited (no lure control). MeSA-baited traps caught greater numbers of adult hoverfly (Toxomerus marginatus), ladybeetles, and lacewings compared with unbaited traps. In another field experiment, predator abundance was monitored using traps placed near the MeSA lure (0 m), as well as at 2.5, 5, and 10 m away from the lure. Adult T. marginatus showed a clear attraction to the point source but not to the other distances. In complementary studies we showed that MeSA emissions from PredaLures dropped quickly soon after deployment in the field but remained relatively high for over four weeks; flowering, but not vegetative, vines were a primary source of MeSA in cranberries; and, exposure to PredaLures triggered elevated MeSA emissions from vegetative vines. In conclusion, insect predators were broadly attracted to MeSA in agricultural fields, including cranberries. Furthermore, this study first demonstrates that PredaLure exposure can elevate MeSA emissions in plants.