Bioefficacy of Allium sativum (L.) Oil and Capsicum annum Miller (Chili Pepper) Fruit Powder Against Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) Infestation in Stored Cowpea Grains

Abstract

The oil and fruit powder of Allium sativum Linn and Capsicum annum Miller (chili pepper) respectively and the combination of both were evaluated in the laboratory (30-35°C and 60-65% RH) against the pulse beetle, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) in cowpea grains. The bioactivity of these plant materials on C. maculatus oviposition, adult (F1) emergence, developmental period, percentage grain damage and percentage adult mortality were assessed on two cowpea grain cultivars (Borno Brown and Borno White) admixed (singly and in combination) at the rates of 0.0% (control) 0.4, 0.8, 1.2 and 1.6% and 0.0% (control), 0.5, 1, 1.5 and 2% (wt/wt) concentration respectively for the latter and other parameters. Except for toxicity test, where 35 adult beetles (zero to three days old) were used, ten pairs of beetles were introduced in each experimental jar for all the parameters tested. All tests were carried out in a complete randomized design (CRD) replicated four times and data generated were subjected to analysis of variance (ANOVA). The number of eggs laid, number of adult beetles (F1) emerged and percentage grain damage significantly (P<0.05) reduced, whilst percentage adult mortality increased on treated cowpea grains of both Borno Brown and Borno White compared to the untreated control. The mean values of all the parameters were generally lower or higher at the highest test concentration i.e., 2 or 1.6% (wt/wt), respectively. Progeny development of C. maculatus was significantly (P<0.05) longer on both cowpea grain cultivars treated with A. sativum oil and A. sativum oil plus C. annum powder to those treated with C. annum powder as well as untreated control. In summary, these results indicate the potential of A. sativum oil and A. sativum oil plus as cowpea grain protectants against C. maculatus infestation especially at higher rates over C. annum powder that proved less effective.