From laboratory to field: electro-antennographic and behavioral responsiveness of two insect predators to methyl salicylate

Methyl salicylate (MeSA) is a commonly emitted herbivore-induced plant volatile (HIPV) known to attract insect predators in agricultural crops. However, thorough studies on whether MeSA can increase their ecological functioning or their attraction under field conditions are still lacking. Here, we conducted laboratory, greenhouse, and field studies to address the hypothesis that two agriculturally important predatory insects (the ladybeetle Hippodamia convergens Gu,rin-M,neville and the lacewing Chrysoperla rufilabris Burmeister) respond physiologically and behaviorally to MeSA, which may lead to increased predation and oviposition. In laboratory studies using electro-antennography, we found that male and female H. convergens and C. rufilabris antennae can detect MeSA; however, for both species, female antennae responded more strongly. In greenhouse studies using cages and wind tunnels, H. convergens females were attracted to, and arrested by, MeSA; this attraction increased egg predation. Attraction of C. rufilabris females to MeSA also increased oviposition. In field studies, mark-release-recapture experiments were performed to investigate H. convergens and C. rufilabris attraction to MeSA over various distances in cranberry fields. More H. convergens and C. rufilabris were caught on yellow sticky cards placed close (0-30 m) to the predator release site than at farther distances, regardless of whether the cards were baited with MeSA or not. In conclusion, H. convergens and C. rufilabris adults detected, and were attracted to, MeSA under laboratory and greenhouse conditions, resulting in higher predation and oviposition, but this attraction was not observed under field conditions. These results demonstrate that predator responses to HIPVs can be complex in real agricultural settings.