Herbivore-induced sorghum volatiles mediate attraction of Cotesia flavipes: roles of DMNT and (Z)-3-hexenyl acetate in tritrophic chemical communication

Abstract

Abstract Herbivore-induced plant volatiles (HIPVs) influence chemical communication among plants, herbivores, and natural enemies and contribute to indirect plant defense. Previous work by our group characterized volatile emissions from sorghum following simulated herbivory and identified DMNT and (Z)-3-hexenyl acetate among consistently induced compounds, but their behavioral activity toward the stem-borer parasitoid Cotesia flavipes was not determined. Four-week-old sorghum (Sorghum bicolor L. Moench) plants were mechanically wounded and treated with Chilo partellus larvae oral secretions. Head-space volatile were analyzed by GC–MS, and female C. flavipes were tested in Y-tube olfactometer assays using volatile extracts from induced and non-damaged plants and their two-component blend. At 24 h, mean emissions of DMNT, (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, and linalool were numerically higher in induced plants than controls; because replicate-level inferential statistics were unavailable, these differences are interpreted descriptively. In Y-tube assays, 28/40 (70.0%) females selected DMNT over hexane (χ2 = 6.40, df = 1, P = 0.011), 30/40 (75.0%) selected (Z)-3-hexenyl acetate (χ2 = 10.00, df = 1, P = 0.002), and 35/42 (83.3%) selected their blend (χ2 = 18.67, df = 1, P < 0.001). Females also preferred induced-plant extracts, with 33/45 (73.3%) selecting them over non-damaged extracts (χ2 = 9.80, df = 1, P = 0.002). These findings demonstrate laboratory behavioral activity of candidate sorghum HIPVs toward C. flavipes. However, they do not establish field sufficiency, concentration-dependent responses, or synergistic interactions. DMNT and (Z)-3-hexenyl acetate therefore represent candidate semiochemicals warranting further validation under ecologically realistic conditions.