Herbivory Triggers Hydrocarbon-Based Semiochemical Defenses Against Aphids in Food Legumes

Herbivore-induced plant volatiles (HIPVs) play critical roles in mediating plant–insect interactions by influencing herbivore behavior and host selection. The present study examined alterations in volatile organic compound (VOC) profiles of cowpea ( Vigna unguiculata ), greengram ( Vigna radiata ), and soybean ( Glycine max ) following infestation by the pulse aphid Aphis craccivora , and evaluated the behavioral effects of dominant long-chain hydrocarbons. Gas chromatography–mass spectrometry (GC–MS) analysis revealed a consistent induction of eicosane, octadecane, and hexacontane in aphid-infested seedlings, indicating activation of a conserved lipid-derived defense pathway across legume species. Behavioral bioassays demonstrated that eicosane and octadecane significantly reduced aphid settlement by 42–47% under both choice and no-choice conditions, even at low (200 ppm) concentrations. These results suggest that A. craccivora perceives hydrocarbon-enriched odor blends as deterrent cues, likely interfering with host recognition or gustatory perception. The findings establish long-chain hydrocarbons as ecologically relevant semiochemicals that mediate direct defense signaling in food legumes and highlight their potential role in shaping aphid–plant interactions within agroecosystems.