Abstract
The cowpea beetle, Callosobruchus maculatus Fab. is an economically important pest of stored grain and causes serious damage to stored peas. The application of pesticides has been the generic control measure due to its effectiveness, affordability and ease of application. However, due to the apparent health and environmental consequences with pesticides, stakeholders are advocating for an alternative management approach that has less social and environmental impact and is more sustainable. Consequently, this study examined the attraction of mated female to volatile blends collected from pods of cowpea plants (Borno-brown and black-eyed cultivars) at three developmental stages developing podsie; 15-17 days after anthesis (daa), fully developed pods (18-20 daa) and mature pods (> 20 daa). The beetles’ responses to the pods’ odour were determined using a two-arm olfactometer, and gas chromatography-mass spectrometry (GC-MS) was used to identify and quantify the volatile compounds collected from the pods. The results showed that female C. maculatus attraction increased with the pod’s age, and that the composition and abundance of volatile compounds varied between cowpea cultivars and the pod’s developmental stage. These findings form an important bases towards developing alternative approach for the management of bruchids.
 Key words: volatile compounds, cowpea plants, GC-MS, pod’s developmental stage, days after anthesis
Highlights
This study examined the attraction of mated female Callosobruchus maculatus to volatile blends collected from pods of cowpea plants (Borno-brown and black-eyed cultivars) at three developmental stages developing podsie; 15-17 days after anthesis, fully developed pods (18-20 daa) and mature pods (> 20 daa)
The results showed that female C. maculatus attraction increased with the pod’s age, and that the composition and abundance of volatile compounds varied between cowpea cultivars and the pod’s developmental stage
Beetle Response to Headspace Volatile Compounds Olfactometer bioassays with natural samples of pod volatiles from Borno-brown beans showed that samples from developing pods ( 2 = 0.051, df = 1, p = 0.820) and fully developed pods ( 2 = 0.170, df = 1, p = 0.679) did not elicit responses from mated females of C. maculatus
Summary
Walp) is an important food and cash crop to farmers (mainly, cowpea growers in tropical regions) and exporting nations. Its production is facing serious pest infestations, especially, from the cowpea bruchid, Callosobruchus. The gravid females of this storage beetle lay eggs on pods of cowpea plant in the field (Taylor and Agbaje, 1974; Ouedraogo and Huignard, 1981; Djossou, 2006; Kebe and Sembene, 2011), and the egg-laden pods are harvested, kept in storage where cross infestations and re-infestations continue. Farmers have to spray pesticides on their harvest to control the pest attack without understanding the consequences of their actions. The risks associated with pesticide usage have been well documented, and has triggered legislation banning its use, and the need for new, safer pest control methods
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