Binary mixture efficacy of NeemAzal and Plectranthus glandulosus leaf powderagainst cowpea and maize weevils
The aim of this study was to determine the insecticidal efficacy of mixture of NeemAzal a commercial neem product and Plectranthus glandulosus leaf powder against Callosubruchus maculatus and Sitophilus zeamais. Mixed at various proportions (100 + 0, 75 + 25, 50 + 50, 25 + 75 and 0 +100%, these powders were tested on adult mortality, inhibition of offspring production and their persistence on C. maculatus and S. zeamais. All the mixed NeemAzal and P. glandulosus caused significant mortality to adult C. maculatus and S. zeamais. No significant difference was observed among the mixed powders that were subjected to the three mixture proportions regarding the mortality they caused to the weevils. The mixed 75% NeemAzal + 25% P .glandulosus of powder led to a higher mortality (100%) of both insect species, three (5 g/kg) days post exposure. The three days LC50 values decreased with ascending proportion of NeemAzal in the mixture from 3.21 g/kg (25% NeemAzal + 75% P. glandulosus) to 0.24 g/kg (75% NeemAzal + 25% P. glandulosus) in S. zeamais. In C. maculatus, the opposing effect was observed. The number of F1 progeny produced reduced significantly (P ≤ 0.01) in both insect species with the mixture proportion of botanicals. The mixtures reduced better the adult progeny production than the botanicals applied alone. The 75% P. glandulosus + 25% NeemAzal persisted well on grains up to 180 days for all dose levels. Powder from NeemAzal and P. glandulosus leaves stand as good candidates to protect maize and cowpea against the infestation of S. zeamais and C. maculatus respectively during storage. Mixing these products could not be advantageous since the binary mixture gave similar result as when they were applied alone.