Host seed type and volatile compound abundance level mould host location and preference behaviours in Callosobruchus maculatus (Fabricius, 1775) (Coleoptera: Chrysomelidae)

Abstract

Dry seeds of cowpea, an important food, and cash crop to farmers, are heavily infested by Callosobruchus maculatus (Fabricius, 1775) during storage, causing huge economic loss. As a result, farmers spray pesticides on their harvest to control the pest attack with little consideration for the consequences of their actions. Due to health and environmental concerns associated with pesticide applications, farmers, marketers, and end-users are seeking alternative safer routes to handling this infestation problem. Thus, this study investigated the response of mated female C. maculatus to odour cues from different bean types using two-arm and four-arm olfactometers. The volatile organic compounds from the preferred beans (Borno brown and black-eyed beans-cultivars of Vigna unguiculata Walper, 1843 and adzuki bean - Vigna angularis (Willdenow) Ohwi & Ohashi, 1969), were analysed using gas chromatography-mass spectrometry (GCMS) techniques and headspace volatile organic compounds were tested in 2-arm olfactometer with the view to identifying possible attractants or deterrents that could be used in effective control of storage pest. The results indicated that (a) the female C. maculatus responded discriminatorily to odour stimuli from the bean types tested, (b) eighteen volatile compounds were present in the bean types tested and (c) the volatile compounds identified varied in abundance profile. These suggest that host location and selection behaviours by female C. maculatus are moulded by the types and concentrations of the volatile compounds present in the beans.