Deterrent Effects of Alstonia boonei Oil on Oviposition and Progeny Development of Callosobruchus maculatus (Fab.) [Coleoptera: Bruchidae].

BACKGROUND: Botanicals insecticides has remained the major weapons amongst tropical zones farmers to combat hexapods infestation of stored cowpea seeds in lieu of expensive synthetic chemical insecticides that have toxic effects on our environment. OBJECTIVES: Deterrence of cowpea bruchid oviposition and emergence on seeds treated with Cheese wood, Alstonia boonei stem bark oil extracted with different solvents was evaluated in dual- and multiple-choice laboratory tests at 28+2oC and 75+5% relative humidity. METHODS: Four rates of oil (1%, 2%, 3% and 4%) or the solvents and an untreated control treatment were replicated four times in Complete Randomized Design. RESULT: The results of the dual-choice test shows that cowpea bruchid laid fewer eggs on cowpea seeds treated with petroleum ether and n–hexane oils of A. boonei stem bark oil compared to the other solvent treated seeds and untreated seeds. The numbers of eggs laid on cowpea seeds treated with 1.0 % oil extracted with methanol, ethanol, acetone, petroleum ether and n-hexane were 3.75 3.00 6.25, 2.25 and 2.00 respectively while the corresponding values for solvents-treated seeds were 9.00, 11.50, 12.50, 6.75 and 4.25, respectively. Generally, oviposition decreased as the concentration (1%, 2%, 3%, 4%) of the oils increased. The results of the multiple choice test shows that untreated cowpea seeds had significantly higher number of eggs than treated seeds. Among the latter, those treated with n– hexane had least numbers of eggs. The numbers of eggs laid on cowpea seeds treated with 2% oil extracted with methanol, ethanol, acetone, petroleum ether and n-hexane were 3.25, 4.00, 7.00, 2.00 and 1.50, respectively. The number of egg laid decreased as the concentration (1%, 2%, 3%, 4%) of the oils increased. Methanol, ethanol, petroleum ether and n-hexane extracts completely inhibited the progeny development of C. maculatus in dual and multiple choice tests. CONCLUSION: A. boonei stem barkoil can control cowpea bruchid infestation on stored cowpea by deterring oviposition and suppressing development.