Cowpea (Vigna unguiculata (L.) Walp) field infestation by the bruchids (Coleoptera: Bruchidae) in the northern Senegal: preliminary biological and ecological data

Abstract

Objective: The objective of this study is to assess, firstly, the effects of distance between the maturing cowpea field and attics storage and secondly the degree of varietal resistance to bruchid infestation Methodology and Results: This study was carried out in the northern Senegal. Three cowpea varieties were used: the Mame Fama, the Baye Ngagne and the Ndiaga Aw. For each cowpea variety, two distances between cowpea fields and cowpea store were considered: one cowpea field situated closer and another one farther from cowpea store. Three cowpea samples were collected and then the level of infestation was calculated. The cowpea pods were preserved in the laboratory to identify the emerging species. Results showed that there was a significant effect of field distances to cowpea store on the eggs laid by weevils (P = 0.02). The number of eggs laid also varied with the cowpea variety. Insects preferred laying their eggs more on the Baye Ngagne cowpea variety than the others. But, the highest rate for emerging species is found on the Mame Fama cowpea variety. The main emerging species identified were Bruchidius atroilineatus (Pic) and Callosobruchus maculatus (F). Conclusion and application: This preliminary study proved that the level of cowpea infestation in the field varied with the proximity of the field to store and cowpea varieties. The Ndiaga Aw cowpea variety was the most resistant one or the least preferred by weevils. Therefore, it is necessary to widely extend this study to more cowpea fields and more cowpea varieties in order to identify some cowpea varieties which will be more resistant to bruchids than others, and make them accessible for cultivators who face many problems for the conservation of their cowpea crops. Key words: Cowpea, Senegal, bruchids, Bruchidius atrolineatus, Callosobruchus maculatus.