Influence of Maize Grain Moisture Content on the Insecticidal Efficacy of Wood Ash, Leaf Powder and Diatomaceous Earth Against Maize Weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Background: Sitophilus zeamais Motschulsky is one of the most important maize pests in developing countries. The application of natural insecticidal powders like inert materials and leaf powders are amongst the many approaches that are used during storage to limit grain losses and are promoted in developing countries. Many factors affect the efficacy of insecticidal powder including the grain moisture content. Materials and Methods: The effect of maize moisture content on the efficacy of Hymenocardia acida Tulasne and Acacia polyacantha Willdenow wood ash, fossilshield (diatomaceous earth) and Plectranthus glandulosus Hook f. leaf powder on adult mortality, progeny inhibition, population suppression and damage reduction of S. zeamais after storage was assessed. Results: The results showed that, at a given dosage within the same period, the mortality of S. zeamais adult decreased when the grain moisture content increased. H. acida, A. polyacantha and P. glandulosus leaf powder at their highest content (40 g kgG1) and fossilshield (2 g kgG1) caused respectively 90, 77.50, 61.25 and 100% mortality at 11% moisture content after 14 days exposure while at 17% moisture content, 56.25, 46.25, 35 and 87.50% mortality was recorded for the respective products. The progeny production was weakly inhibited by the different powders when the grain moisture content increased. Maximum suppression of population as well as the reduction of damage was observed at the lowest moisture content (11%). Conclusion: The studied products are efficient to control infestation by S. zeamais, but their efficacy decreased by the rise of grain moisture content. Therefore for a better grain storage, good drying of maize grains combined with the application of botanical powders is recommended.