Interrelation between Surface Wax Alkanes from Red Kidney Bean (Phaseolus vulgaris L.) Seeds and Adzuki Bean Weevil [Callosobruchus chinensis (F.)] (Coleoptera: Bruchidae)

Abstract

Background: Callosobruchus chinensis (Fabricius) (Coleoptera: Bruchidae) is one of the major insect pests of Phaseolus vulgaris L. grains, commonly known as rajma seeds, in Europe and Asia including India. Infestations of these insects destroy majority of legume seeds including rajma which causes a great economic loss. Hence, a proper sustainable pest management measures are necessary for storage of rajma seeds. For this, the study aims to identify and quantify the n-alkane profile from the surface waxes of rajma seeds and their role as olfactory cue in C. chinensis. Individual synthetic alkane followed by the synthetic blends mimicking rajma seed surface wax n-alkanes as olfactory cue was also evaluated.Methods: Collected rajma seeds were solvent extracted to isolate surface waxes. The extract then fractioned by thin-layer chromatography and followed by gas chromatography-mass spectrometry analyses to purify, quantify and identify n-alkanes.Result: Rajma seeds’ surface waxes analysis revealed 18 n-alkanes between n-C15 and n-C33. The predominant alkanes were n-octacosane and n-hexadecane. n-Octadecane was the least abundant alkane in seeds. Total alkane content was 3502.67±12.82µg from 100 g (number 200 ± 5.13) seeds. Adult female C. chinensis elicited attraction towards the surface wax alkanes at concentrations of 0.5, 1, 2, 4 and 6 seed(s) equivalent of rajma seed(s) in the Y-tube olfactometer bioassay, but the highest attraction was observed at 6 seeds equivalent. Hence, a synthetic alkane blend resembling of 6 seeds equivalent, present in seeds’ surface wax alkane or a combination of nine (which elicited positive response) synthetic alkane blend resembling 6 seeds equivalent could be used as lures in developing baited trap in insect pest management programme.