Abstract
The bioactivity of Alstonia boonei De Wild (Apocyanaceae) against Callosobruchus maculatus (Fab.) (Coleoptera: Chrysomelidae) in stored cowpea seeds was evaluated in the laboratory by admixing leaf, stem bark and root powders of A. boonei with cowpea seeds at ambient temperature of 28+20C and 70+5% relative humidity. The powders were incorporated into 20g of cowpea seeds, Vigna unguiculata at 0.0% (control) 2.5%, 5.0%, 12.5% and 25.0% (w/w) concentration. The ability of the plant powders to protect cowpea seeds was assessed in terms of mortality rates after 24 - 96 hours post treatment, oviposition and adult emergence, percentage weight loss and damage after the first filial generation (F1). All the tested plant part powders significantly (P<0.05) reduce the longevity of adult C. maculatus on treated cowpea seeds. From the study, the plant powders could be ranked in order of effectiveness thus; stem bark > leaf > root. Alstonia boonei can be used as biopesticide against C. maculatus and its incorporation into traditional storage pest management is strongly recommended.
Highlights
Cowpea bruchid, Callosobruchus maculatus (Fab.) is a major pest of wide range of stored legume seeds especially of the cowpea, Vigna unguiculata (Ofuya 2001)
They were subsequently reared inside 1 litre Kilner jars, on uninfested cowpea seeds Vigna unguiculata variety Ife brown obtained from the Agricultural Development Programme (ADP), Ado Ekiti
Stem bark and root powders of Alstonia boonei tested at 5% level showed similar bioactivity against Callosobruchus maculatus after 96 hours of post treatment
Summary
Callosobruchus maculatus (Fab.) is a major pest of wide range of stored legume seeds especially of the cowpea, Vigna unguiculata (Ofuya 2001). In many countries of Western and Central Africa, cowpea is a major dietary staple. It is often the main source of protein for the families. Cowpeas are rapidly broken down by the cowpea weevil within three to five months in storage (Ajayi & Lale, 2000; Mbailao et al, 2006). The cowpea weevil causes heavy qualitative and quantitative losses. Preservation of the quality of the seeds for the following year is one of the worrying problems of farmers. The heavy post harvest losses and quality deterioration caused by storage pests is a major problem facing agriculture in developing countries such as Nigeria (Ashamo, 2007)
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