Preference of flight morph of Callosobruchus maculatus (Coleoptera: Chrysomelidae) for three plant legumes

Abstract

AbstractWe studied host discrimination in flight morph ofCallosobruchus maculatus(F.) among the legume plants Ife-brown (IB) and black-eyed (BE) cowpea,Vigna unguiculata(L. Walp), soybean (SB), andGlycine max(L.) and analysed legume volatiles towards developing an attractant forC. maculatus. Olfactometry studies were conducted to investigate attraction of mated 3–4-day-old femaleC. maculatusto legume plants with the green pod (PGP), green pods (GP), plant with the ripened pod (PRP), ripened pod (RP), and plant without pod (PWP). We also assessed the response of beetles to phenological stages of the most attractive legume. In Y-tube bioassays,C. maculatusshowed greater attraction to individual legumes at three phenological stages: PGP (73–93%), PRP (80–100%), and RP (63–93%) compared with PWP (6–36%). In four-choice bioassays,C. maculatuspreferred IB at all stages to other legumes. SB had an insignificant attraction on the beetle. The RP of IB was the most attractive part of the plant. Gas chromatography (GC) and GC–mass spectrometry (GC–MS) analyses of volatiles emitted by RP of the legumes revealed a variation in the compositions of odour blends. Benzaldehyde was found in the volatiles of IB and BE with a higher emission in IB. Octanone was detected only in IB. The two compounds were undetected in SB volatiles. These results reveal that in addition to infesting cowpea plants at RP stage as reported in previous studies,C. maculatuscould also infest cowpea plants at the GP stage.