Insecticidal Activity of Alstonia boonei De Wild Powder against Cowpea Bruchid, Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae] in stored Cowpea Seeds

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.