Evaluation of cowpea genotypes for resistance to the legume pod borer, Maruca Vitrata (Fabricius) (Lepidoptera: Pyralidae)

Abstract

16 cowpea varieties were screened for resistance to the legume pod borer, Maruca vitrata F. under natural infestation in the field. Plants were planted in a  randomized complete block design in three replicates; each plot consisted of four rows, 3m long. Spacing was 1.5m between plots and 0.75m between  rows. Intra- row spacing was 0.2m.Two weeks prior to planting experimental materials, a susceptible cultivar was planted perpendicular to every range of  rows within a plot to serve as a reservoir of the test insect, M.vitrata. Plants were sprayed with Monocrotophos at 200g a.i /ha once at the vegetative  stage and at the onset of flower bud initiation and later during podding to control other pests apart from Maruca. Larval density, flower damage, pod  damage, seed damage, pod load (a measure of the degree of successful pod production) and Index of pod evaluation (Ipe), calculated as [PL X (9-PD)], (a  measure of the varietal performance of the cowpea genotypes) were used to assess resistance in cowpea varieties. Significant variations were observed  in the level of resistance among the cowpea genotypes in the field. The findings show that Tvu 4578 is resistant while Tvu 1544, IT97K-499-35, IT93K452-1  and IT90K-76 show promising level of resistance. The probable factor contributing to resistance may be non- preference or host plant resistant factors.