Semiochemical modulation of host preference of Callosobruchus maculatus on legume seeds

Host preference of Callosobruchus maculatus (F.) on seeds of three legume cultivars, Ife-brown and black-eyed cowpeas [Vigna unguiculata L. (Walp)], and soybean (Glycine max L.), was investigated. Mated female C.maculatus showed high (90-95%) attraction to the three legume cultivars in Y-tube bioassays. However, the weevils discriminated among the cultivars in four-choice tests and showed greater attraction to Ife-brown cowpea (50%) than to soybean (30%) and black-eyed cowpea (15%). Coupled gas chromatography-electroantennography (GC-EAD) and GC-MS analyses of the headspace volatile organic compounds (VOCs) emitted by the legume seeds identified 2-ethyl hexanol as the principal EAD active component. Emission of 2-ethyl hexanol was two-fold greater in Ife-brown cowpea (~0.54μgg^-1 seeds) compared with black-eyed cowpea (~0.23μgg^-1 seeds) and soybean (~0.21μgg^-1 seeds). Synthetic 2-ethyl hexanol attracted 68% of female C.maculatus at 0.01μg dose in Y-tube bioassays. These results demonstrated that host preference in C.maculatus is odor-mediated, and identified 2-ethyl hexanol as a potential attractant for C.maculatus.