Potential of seed dusts of Jatropha curcas L., Thevetia peruviana (Pers.), and Piper guineense Schumach. against the maize weevil, Sitophilus zeamais (Motschulsky, 1855) (Coleoptera: Curculionidae) in storage of corn grain

A laboratory evaluation was carried out to determine the efficacy and phytochemical composition of powdered seeds of Physic nut Jatropha curcas , Yellow oleander Thevetia peruviana and West African black pepper Piper guineense at different dosages (2.5, 5.0, 7.5 and 10.0 g) for the management of Sitophilus zeamais . Treatments were mixed with 50 g of maize and infested with 10 adult S. zeamais in 200 ml air-tight glass vials and kept under ambient conditions (25-30°C and 70-90 RH) for a period of 28 days in August 2015. The trial was laid out in a completely randomized design in four replicates. Results from data analyses showed that treated maize grains in storage recorded significantly (P < 0.05) higher mean mortality levels of adult S. zeamais than the untreated controls. However, there were no significant differences in mean mortality of the weevil at 7, 14, 21 and 28 DAT, except on those stored only for 1 DAT. Batches treated with higher doses (10.0, 7.5, 5.0 g) suffered a higher total mortality of adult S. zeamais ; this was significantly (P < 0.05) higher compared with treatments using smaller dosages (2.5 and 0.0 g). Phytochemical analysis of treatments revealed high levels of alkaloids, tannins and phenols in all the plant extracts. The flavonoid contents were also high in Piper guineense and Permethrin, but lower in Jatropha curcas and Thevetia peruviana . These compounds are known to possess insecticidal properties that may have been responsible for the mortality of Sitophilus zeamais.