Effect of Smoke from Senna Siamea (Lambk) on Sitophilus Zeamais (Motschulsky) in Stored Maize

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The use of botanical protectants in traditional management of storage pests in the tropics cannot be overemphasized. Earlier studies on the use of smoke from twigs of Senna siamea (Lambk) (Syn. Cassia Siamea) revealed that the smoke minimized insect pest damage and prevented the growth of some storage fungi. The objective of the study was to evaluate the insecticidal, repellence, persistence and fungicidal properties of the smoke on maize in smoke fumigation chambers. In a completely randomized design, clean and whole-grained shelled and dehusked Obatanpa maize variety was infested and fumigated against the various developmental stages of Sitophilus zeamais (Motshulsky) « (Coleoptera:Curculionidae). The differences in numbers of the weevil that emerged when maize containing the different developmental stages of the weevil was fumigated, were not significant. The smoke did not exhibit any significant insecticidal effect on the insects on dehusked (intact) cobs. Increasing the duration of fumigation from 1 hour to 4 hours, had no significant effect on the insects on shelled maize. Fumigating undehusked cobs, for 1, 2, 3 and 4 hours and sampled at 1, 4, and 8 weeks after fumigation, showed significant reduction in infestation and damage when compared with unfumigated maize for all the durations of fumigation. To assess the repellency of the smoke, a modified Mohan and Field (2002) technique was used. Plastic bottles; measuring 20 cm x 5 cm (height and base diameter respectively) with holes created at an interval of 1 cm were used. The set - up was replicated three times with 300 g of maize fumigated for 4 h. The greatest number of the weevil was repelled during the 1st hour of exposure with decreasing numbers at 24h and 48 h. Three hundred grams of shelled maize was also fumigated for 4 h and assessed for contact toxicity. Mortality was recorded at 1, 24 and 48 hours after fumigation. The fumigated maize grains did not exhibit'any contact toxicity on the pest. Fumigating the adult Szeamais for 1 or 4 hours did not kill the weevils. Obatanpa maize variety, fumigated for 1, 2, 3 and 4 hours, were evaluated for their health status using the Blotter method. There were no significant differences in the incidence of Aspergillus flavus, Fusarium verticelloides and Penicillium sp after * fumigation. Although the fumigated maize had no contact toxicity and the smoke did not kill the fumigated weevils, the fumigation exhibited a repellent activity on S. zeamais. The twigs of S. siamea can therefore be used in traditional post harvest systems where fire is set under maize barns and platforms. Burning the twigs under such structures will result in the pest been repelled by the smoke.