Response of 20 varieties of cowpea (Vigna unguiculata (L.) Walp) to Bruchidius atrolineatus P. and Callosobruchus maculatus F. (Coleoptera-Bruchidae)

Doumma, A.; Liman, A.I.; Toudou, A.; Alzouma, I.

Cahiers Agricultures 15(2): 187-193


ISSN/ISBN: 1166-7699
Accession: 004469040

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B. atrolineatus and C. maculatus (Coleoptera-Bruchidae) are the most important pests of cowpea beans, V. unguiculata. In the Sahel, cowpea infestation by these two bruchid species starts in the field when the plant begins to bear fruit and continues through storage, resulting in substantial damage if no control action is taken. In this study, we examine the reaction of 20 cowpea cultivars to these two bruchid species in the Sahelian zone of Niger. The field trial was carried out with a random block system with 4 repetitions. At maturity, 100 pods were harvested of each cultivar and distributed in two parallelepipedal dishes, 50 pods by dish. We counted the eggs, emergence holes, and number of bruchids. Field and storage results showed satisfactory response for some of the cultivars tested, that is, low levels of bruchid infestation. Initial field infestation was generally very low, although cultivars such as 049-84, 050-84 and TN5-78, with more than 69 bruchid eggs, were relatively infested. The global result during storage showed TN5-78, TN3-78, 057-84 and IT90K372-1-2 were the most heavily infested cultivars, with an average of more than 124 eggs per pod. On the other hand, 034-84, 048-84, 019-84, 078-84, 063-84, and 041-84 had less than one egg per pod during storage. The analysis of the evolution of bruchids' egg-laying activity showed that the number of eggs, very low at the beginning of storage, increased markedly during storage. It nonetheless varied according to cultivar. It was highest for TN5-78, IT90K372-1-2, 057-84, 028-84, and 022-84, and very low for 034-84, 041-84, and 019-84. Results were the same for the emergence of adults. There were very few adult bruchids at the beginning of storage, but the number increased considerably in all batches. Again, however, it varied according to cultivar. It was highest for 028 -84, TN5-78, IT 90K372-1-2, 057-84, TN3-78 and 022-84, and lowest for 078-84, 034-84, 048-84, 041-84, 063-84, 019-84, TN121, and 050-84 during the overall storage period, with less than one emergence hole per pod. For some cultivars, the number of adult bruchids was not proportional to the number of eggs deposited. Comparison of rate of emergence and number of eggs deposited according to cultivar showed, for example, that of 028-84, which received fewer eggs than TN5-78, had a relatively higher emergence rate. This suggests that the cultivars tested do not all have the same mechanism of resistance. The use of resistant cultivars appears a promising method for protecting cowpeas from bruchid attacks.