Comparative GC–MS profiling of aphid-associated volatile hydrocarbons and preliminary screening of their anti-aphid activity

Aphid infestation can modify plant volatile chemistry, generating complex chemical signatures that may influence herbivore interactions. This study characterized volatile metabolites associated with aphid infestation in five economically important crop–aphid systems: maize– Rhopalosiphum maidis , cowpea– Aphis craccivora , groundnut– A. craccivora , brinjal– A. gossypii and mustard– Lipaphis erysimi . Volatiles from aphid-infested seedlings were collected by dynamic headspace sampling and analysed using GC–MS. Across the five systems, 85 putatively identified volatile metabolites were detected, with distinct crop-specific compositions and relative abundances. Principal component analysis and hierarchical clustering differentiated the crop–aphid combinations and highlighted metabolites contributing to their chemical profiles. Six hydrocarbons—eicosane, 5-methyl octadecane, 1,2,4-trimethylcyclohexane, 2,6,10,15-tetramethylheptadecane, henicosene and 1-heptene-2-isohexyl-6-methyl—were selected for laboratory evaluation based on their occurrence, relative abundance and distribution among aphid-associated profiles. At 200 and 500 ppm, eicosane and 5-methyl octadecane produced the most consistent reductions in aphid abundance after 48 h. Because this endpoint does not distinguish mortality from altered settling, retention, dispersal, feeding effects or population increase, the responses are interpreted as preliminary aphid population suppression rather than evidence of a specific pesticidal or behavioural mechanism. As healthy, uninfested seedlings were not profiled in parallel, the metabolites are considered aphid-associated rather than statistically demonstrated aphid-induced metabolites. Compound identities were putatively assigned using mass-spectral library matching and retention-index comparisons. The study provides a preliminary chemical-discovery and functional-screening framework for prioritizing candidate compounds, with authentic-standard confirmation and further biological validation required before semi-field or field evaluation.