Corn volatiles as attractants for northern and western corn rootworm beetles (Coleoptera: Chrysomelidae: Diabrotica spp)

Synthetic corn volatiles and selected analogs were tested in commercial corn fields for attractiveness to feral northern (NCR, Diabrotica barberi) and western corn rootworm beetles (WCR, D. virgifera virgifera). Two new attractants, geranylacetone and a-terpineol, were identified among corn terpenes and compared at four stages in crop development with the phenylpropanoid standards cinnamyl alcohol and 4-methoxy-cinnamaldehyde, with each component at 30 mg/trap. Dose-response relationships (0.1-100 mg/trap) and efficacy of two-component blends (30 mg/component) Cere also examined. More beetles were captured on traps baited with (+)- than (-)-alpha-terpineol, but the difference was statistically significant only for WCR. Captures with geranylacetone or (+)-alpha-terpineol were directly proportional to the logarithm of the attractant dose. WCR females were attracted to as little as 0.1 mg of either compound. WCR males required greater than or equal to 1.0 mg of (+)-alpha-terpineol and were not attracted to geranylacetone at any dose. NCR required greater than or equal to 0.3 mg of either attractant and showed less marked response differences between the sexes than did WCR. Geranylacetone and cinnamyl alcohol were equally effective attractants, whereas (+)-alpha-terpineol was significantly less attractive to WCR but more attractive to NCR than was 4-methoxycinnamaldehyde. Corn terpenes and phenylpropanoid standards produced similar seasonal response patterns in that captures tended to rise in each case as the season progressed, except during silking when no compound was attractive. Mixing corn terpenes or phenylpropanoid standards synergized responses of WCR females, but (+)-alpha-terpineol suppressed attraction of NCR females to geranylacetone.