BEHAVIOURAL RESPONSES OF Callosobruchus maculatus (FABRICIUS) TO THREE VOLATILE ORGANIC COMPOUNDS OF COWPEA

Abstract

In this study, a Y-tube olfactometer was used to investigate the behavioural responses of C. maculatus to three volatile organic compounds (VOCs) (hexanal, decanal and menthol). Ethanol was used to prepare different concentrations of VOCs and it (ethanol) also serve as the control. A preliminary test was carried out on the olfactory response of C. maculatus to individual VOCs at concentrations of 10, 20 and 30 μgg-1 in order to determine the attraction of C. maculatus to the compounds. Further studies was carried out at lower concentrations of 0.1, 0.2, 0.3μgg-1 of the VOCs to better understand the individual effect of the VOCs on C. maculatus. Different mixing ratios (1:3, 1:1 and 3:1) of two of the most effective VOCs at concentration of 0.1-0.3 μgg-1 were used to determine the synergetic effects of the compounds on C. maculatus. The preliminary test results showed that the insects were confused, and there was a significant difference (P<0.05) between the VOCs and control except for females tested with decanal. The decision time required by C. maculatus tested with hexanal (9.17 mins) and decanal (7.97 mins) was not significantly different (P>0.05). The percentage of C. maculatus that respond positively to VOCs at 10-30 μgg-1 was very low when compared with the percentage of the insects that showed no response (up to 100%). However, at concentrations of 0.1-0.3 μgg-1, the percentage of C. maculatus attracted to VOCs showed that there were significant difference (P<0.05) when compared with the result of the control (ethanol) for both sexes. Similarly, the highest and the lowest percentages of positive attraction were elicited by hexanal and menthol, respectively at concentrations of 0.1-0.3 μgg-1. Both hexanal and decanal also showed higher percentages of attraction than menthol. Also, hexanal, decanal and their mixtures at different ratios caused the attraction of more C. maculatus females than the males. The percentage attraction of C. maculatus to the mixtures of hexanal and decanal was higher than the individual VOCs. The various results obtained in this study showed that the mixture of hexanal and decanal could be used as effective bait for the management of C. maculatus, the notorious pests of cowpea seeds in Nigeria.