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ABSTRACT
Studies on the repellent and insecticidal potential of the invasive alien plant, Mimosa diplotricha C. Wright ex Sauvalle (Mimosaceae) are non-existent, hence this study evaluated the repellency and insecticidal activities of the leaf and stem powders of the weed against the maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) under laboratory conditions. Maize grains infested with the adults of S. zeamais were exposed to three concentrations viz. 1.5g, 2.5g and 3.5g of M. diplotricha leaf and stem powders for 3 hours after which percentage repellency was calculated. Also, adult weevils were exposed to grains treated separately with one of three concentrations (1.5g, 2.5g and 3.5g) of the leaf and stem powders of M. diplotricha at different exposure periods. Percentage survival was recorded every 24 hours over a 120-hour period. The leaf and stem powders of M. diplotricha exhibited some degrees of repellency against S. zeamais, although the repellent activity was a function of both concentration and exposure time. Following a 3-hour exposure period, the 3.5g of the leaf (53%) and stem (58%) powders exhibited the highest repellent activity against S. zeamais. Although the leaf and stem powders of M. diplotricha plants exhibited some degrees of mortality against S. zeamais, it was observed to be concentration and exposure time dependent. At a the highest concentration (3.5g), the leaf and stem powders of M. diplotricha accounted for only 28% mortality (72% survival) of S. zeamais after a 120-hour exposure period. Although this study demonstrated the repellent and insecticidal activities of the leaf and stem powders of M. diplotricha against S. zeamais, for the first time, it however suggests that the plant powders tested possesses poor insecticidal activities against the weevil, hence studies on the efficacy of the leaf, stem or root extracts of the plant are recommended.
