Momordica cochinchinensis (Cucurbitaceae) leaf volatiles: semiochemicals for host location by the insect pest, Aulacophora foveicollis (Coleoptera: Chrysomelidae)

Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) and Epilachna dodecastigma (Wied.) (Coleoptera: Coccinellidae) are important herbivore pests of Momordica cochinchinensis Spreng (Cucurbitaceae). The volatile organic compound (VOC) profile from undamaged and mechanically damaged plants, and from plants 24 h and 120 h following continuous feeding of adult female A. foveicollis and E. dodecastigma, was identified and quantified by GC-MS and GC-FID analyses. Twenty-two compounds were identified in volatiles of undamaged plants and in 24-h and 120-h post-insect-feeding plant volatiles; whereas 21 components were detected in volatiles of mechanically damaged plants. With the exception of four compounds, 1-heptanol, 3-octanone, acetophenone and nerolidol, the emissions of all other compounds were significantly increased following insect attack. In all plants, phytol was predominant, followed by geranyl linalool and linalool. Only 2-hexanol was unique to mechanically damaged plants, and 1-octen-3-ol and farnesyl acetone were detected in volatiles of undamaged and insect-damaged plants, but not in volatiles of mechanically damaged plants. However, none of these volatile components, when tested individually, showed attraction to A. foveicollis in Y-shaped glass tube olfactometer bioassays. Aulacophora foveicollis elicited significant preference for the whole volatile blends from insect-damaged plants compared to those of undamaged plants, and volatiles from 120-h post-E. dodecastigma feeding plants were more attractive to A. foveicollis compared to those from conspecifically damaged plants. Furthermore, the finding that A. foveicollis responds to individual synthetic compounds, 1-heptanol, 3-octanol, linalool oxide, 1-octanol, nonanal, geranyl linalool and phytol, and provide a basis for new inventions on trapping tools for pest management strategies.