Influence of Duration of Storage of Insecticidal Plant Oil and Oil-treated seeds on the Efficacy of Neem Seed Oil in the Control of Callosobruchus maculatus (F.) Infesting Stored Cowpeas

MAINA, Y.T. and LALE, N.E.S.

The effect of duration of storage of insecticidal plant oil after extraction and oil-treated seeds prior to infestation on efficacy of neem (Aradirachta indica) seed oil (NSO) in the management of Callosobruchus maculatus (F.) infesting cowpeas in tropical storage was investigated in two separate experiments. In the first experiment, the influence of five durations (0, 7, 12, 26 and 82 months) of storage after extraction on the potency of three dosages (0.04, 0.08 and 0.16 ml) of NSO in controlling C. maculatus was tested using 20g of cowpeas. At the dosage of 0.04 ml/20g seed, there was no significant difference in the mean numbers of eggs laid on cowpeas treated with NSO that had been stored for the indicated periods. For the dosages of 0.08 and 0.16 ml/20 g seed. the mean numbers of eggs laid on cowpeas treated with oil that had been stored for 82 months were significantly higher than those laid on cowpeas treated with NSO that was extracted and applied immediately or oil that was stored for 7 or 12 months before application. There were no significant differences in t.he potency of NSO of the different storage periods in suppressing progeny development. At each age of NSO, significantly fewer C. maculatus adult progenies developed in cowpeas treated with the three dosages of oil than in the untreated seeds and no adult progeny developed in cowpeas treated with 0.16 ml of NSO. Similar trends were observed for percentage of seeds damaged by C. maculatus. In the second experiment, the influence of time interval between application of NSO and infestation of treated cowpeas with C maculatus was investigated. With only an occasional exception, duration of storage of NSO-treated cowpeas prior to infestation had no significant effect on the potency of the oil to reduce C. maculatus adult progeny development especially at the dosages of 0.08 and 0.16 m1/20 g seed. No adult progeny developed and no damage occurred in cowpeas that were infested immediately after treatment with the dosage of 0.16 ml/20 g or in seeds that were infested one month after treatment with oil.

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