Abstract
<p>Laboratory study was carried out to investigate the efficacy of hymenopteran parasitoids, (<em>Dinarmus basalis</em> and <em>Choetospila elegans)</em> parasitization of <em>Callosobruchus maculatus</em> on cowpea (<em>Vigna unguiculata</em>) seeds in the Department of Crop Science, University of Calabar, Nigeria. Treatments were the inoculation of <em>D. basalis</em> (sole), <em>C. elegans</em> (sole), a mixture of <em>D. basalis</em> and <em>C. elegans</em> into infested cowpea seeds and the control which received no parasitoids. The introduction of parasitoids was repeated at 3 d interval, and all treatments were replicated 3 times. Result indicated that early introduction of the parasitoids caused significantly (P ? 0.05) higher mortality of <em>C.maculatus</em> than late introduction. Mix culture of both parasitoids was significantly more efficacious than sole culture. The emergence of each parasitoid and the mortality of <em>C. maculatus</em> in sole culture showed a highly significant (P ? 0.01) positive relationship (r = 0.487) between <em>C. maculatus</em> and <em>D. basalis</em> but non-significant (P ? 0.05) though positive association (r = 0.289) with <em>C. elegans</em>. A multiple regression analysis between <em>C. maculatus </em>mortality and the emergence of the two parasitoids in mix culture also indicated a highly positive significant (P ? 0.01) relationship (R = 0.751, R<sup>2</sup> = 0.564). Pearson Correlation analysis also showed a significant (P ? 0.05) positive association (r = 0.464, and 0.401) between <em>C. maculatus</em> mortality and emergence of <em>C. elegans</em> and <em>D. basalis</em> in mix culture, respectively. However, a non significant (P ? 0.05) negative relationship (r = -0.336) was observed between the two parasitoids in their emergence in mix culture, but <em>D. basalis</em> contributed more to the mortality of <em>C. maculatus</em> than <em>C. elegans</em>. Data from this study showed that <em>D. basalis</em> and <em>C. elegans</em> have potentials to be deployed as biological control entities in the management of <em>C. maculatus</em> as a part of the integrated pest management strategies of storage pests in the tropics.</p>
Highlights
Cowpea [Vigna unguiculata (L.) Walp.] is one of the most widely adapted, versatile and nutritious grain legumes, and has been consumed by humans since the earliest practice of agriculture in developing counties of Africa, Asia and Latin America, where it is especially valuable as a source of dietary proteins as well as vitamins and minerals (Singh et al, 2003; Langyintuo et al, 2003; Ukeh & Udo, 2008)
Data from this study showed that D. basalis and C. elegans have potentials to be deployed as biological control entities in the management of C. maculatus as a part of the integrated pest management strategies of storage pests in the tropics
Data from this study showed that adult C. maculatus started to emerge at 20 days after oviposition while the parasitoids emerged from 12 days after inoculation in each experimental culture
Summary
Cowpea [Vigna unguiculata (L.) Walp.] is one of the most widely adapted, versatile and nutritious grain legumes, and has been consumed by humans since the earliest practice of agriculture in developing counties of Africa, Asia and Latin America, where it is especially valuable as a source of dietary proteins as well as vitamins and minerals (Singh et al, 2003; Langyintuo et al, 2003; Ukeh & Udo, 2008). The cowpea beetle, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) is a tropical insect that develops in the seeds of Vigna unguiculata (L.) Walpers (Zannou et al, 2003). According to IITA (1989) C. maculatus consumes 50-90% of cowpea in storage annually throughout tropical Africa. The bruchid infestation affects seed quality, market value and can reduce cowpea seed viability to 2% after three months of storage (Ofuya & Credland, 1995; Ukeh et al, 2011).
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