Behavioral responses of a herbivorous mite and its potential predatory mirid to synthetic plant volatiles

Herbivore-induced plant volatiles (HIPVs) mediate tritrophic interactions among plants, herbivores and their natural enemies. Using Y-tube olfactometer bioassays, we evaluated the behavioral responses of the zoophytophagous predator Macrolophus pygmaeus (Hemiptera: Miridae) and the herbivorous mite Tetranychus urticae (Acari: Tetranychidae) to ten synthetic volatile compounds associated with HIPV blends emitted by pepper (Capsicum annuum) plants under herbivore attack. Each compound (methyl salicylate [MeSA], farnesene, [mix of isomers] decanal, (+)-3-carene, (−)-β-pinene, (1S)-(−)-α-pinene, nonanal, hexanal, (Z)-3-hexenyl acetate, and 1H-indole) was tested at three concentrations (1, 10 and 100 ppm) against a hexane solvent control. At 100 ppm, M. pygmaeus was significantly attracted to MeSA and farnesene and significantly repelled by (+)-3-carene; neither attractant elicited a response at 10 ppm. Tetranychus urticae showed no attraction to any compound but was strongly repelled by (+)-3-carene at all three concentrations tested. Results demonstrate that HIPVs can differentially influence predator and herbivore behaviour in a dose-dependent manner. The identification of (+)-3-carene as a potent repellent for T. urticae and of MeSA and farnesene as attractants for M. pygmaeus provides a basis for volatile-based IPM strategies that integrate pest deterrence with natural enemy attraction within the crop, which could represent a practical tool supporting conservation biological control in pepper.