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

摘要

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℃ and 60 - 65% RH) against the pulse beetle - Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) infestation of stored 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), 0.5/0.4%, 1/0.8%, 1.5/1.2% and 2/1.6% (wt/wt) concentration. Ten pairs or 35 adult beetles (zero to three days old) 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 the analysis of variance (ANOVA). The number of eggs laid, number of adult beetles (F_1) emerged and percentage grain damage significantly (P<0.05) reduced compared to the untreated control, whilst percentage adult mortality increased on treated cowpea grains of both Borno Brown and Borno White. The mean values of all the parameters were generally lower or higher at the highest test concentration, 2/1.6% (wt/wt), respectively. Progeny development of C. maculatus was significantly (P<0.05) longer on cowpea grains of both cultivars treated with A. sativum oil and A. sativum oil plus C. annum powder than on those treated with C. annum powder as well as untreated control. In summary, these results indicate the relatively high potential of A. sativum oil and A. sativum oil plus C. annum powder as cowpea grain protectants against C. maculatus infestation especially at higher rates over C. annum powder that proved less effective.