ABSTRACTTrials were carried out in both screen house and field during 2014 cropping season at Samaru, Zaria to study the Economic Injury Levels (EIL) and to evaluate some cowpea varieties for field resistance to legume pod borer (Maruca vitrata (G.) Fab). First instar larvae of M. vitrata at levels 0 (no larvae were released), 5, 10, 15, 20, 25 and 0, 25, 50, 75, 100, and 125 were used to infest (SAMPEA 7) cowpea at flower bud initiation, 50 % flowering and 50 % podding in both screen house and field cages, respectively. The treatments were arranged in a Complete Randomized Design (CRD) and Randomized Complete Block Design (RCBD) replicated four times for screen house and field trials, respectively. Parameters assessed include, number of pods produced, damaged pods, weight of grains and the rate of association between larval density and grain weight. The result obtained showed decreased yield in cowpea with increase in number of larvae infested in both screen house and field cages. Infestation with 5 and 25 larvae per cage, caused decrease in yield from 549.75 kg ha-1 and 843.50 kg ha-1 in screen house while infestation with 25 and 125 larvae caused a decrease of 486.25 kg ha-1 and 222.50 kg ha-1 in field cages. The estimated Economic Injury Levels (EIL) in the screen house was 0.13, 0.14, 0.14, 0.13 and 0.15 when Cypermethrin, Dimethoate, Chlorpyriphos, Cypermethrin plus Dimethoate and Imidachloprid, respectively were sprayed to control Maruca. The corresponding values for field cages were 0.14, 0.15, 0.14, 0.14 and 0.16, for the respective insecticides. Twelve cowpea varieties were also assessed for resistance to Maruca vitrata using three sowing dates at two weeks interval. The experiments were laid out in Randomized Complete Block Design (RCBD) replicated three times. Based on the percentage pod damage, damage score for each variety was given resistance rating 1-5. The results showed that the first sowing date (early August) had less infestation by M. vitrata and differed significantly (p<0.05) from those sown in late August to early September. All the varieties sown early August to late August had less Maruca infestation and produced higher grain yields than those sown early September. Wild cowpea (Vigna dekendtiana) was highly resistant and differed significantly (P< 0.05) from the cultivated varieties, while SAMPEA 1, 4, 6, 9 and 10 were the most susceptible varieties with higher pod and seed damage and lower grain yields. SAMPEA 7, 8, 11, 12, 14, and15 were moderately resistant. None of the variety was resistant or highly susceptible to the Maruca vitrata attack. Therefore, highly resistant and moderately resistant varieties can be utilized by the farmers and in breeding programme for the management of pod borer as a component of IPM.
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