Influence of carrier solvent on the efficacy of neem (Azadirachta indica A. Juss) seed oil applied for the control of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Abstract

The influence of four carrier-solvents (acetone, ethanol, petroleum ether and hexane) on the efficacy of neem (Azadirachta indica A. Juss) seed oil applied at the rate of 0.04 ml/33 ml of cowpea seeds and tested on the cowpea seed bruchid, Callosobruchus maculatus (F.), was assessed under tropical storage conditions. Neem seed oil (NSO) applied in ethanol or hexane, on average, reduced egg-laying, percentage of seeds infested with bruchid eggs, adult progeny development and severity of seed damage (number of adult emergence holes per seed) significantly more than application of NSO in acetone or petroleum ether. Cowpea seeds treated with NSO applied in 0.4 or 0.6 ml of the carrier solvents were, on average, infested significantly less with bruchid eggs than seeds treated with NSO applied in 0.2 ml of the solvents. Adult progeny development decreased as the volume of solvents increased and no adult progeny developed in seeds treated with NSO applied in 0.8 ml of ethanol. Severity of seed damage was significantly lower (1.17) in seeds treated with NSO applied in 0.8 ml than in seeds treated with pure NSO (1.59). Application of NSO in hexane reduced the percentage of seeds damaged by C. maculatus significantly more than application of the oil in petroleum ether and seed damage was lowest in batches of cowpea seeds treated with oil applied in 0.8 ml of the solvents.