Effectiveness of binary combinations of Plectranthus glandulosus leaf powder and Hymenocardia acida wood ash against Sitophilus zeamais (Coleoptera: Curculionidae)

Combinations of botanicals could enhance biological activity against insects. This in turn, will reduce amount of botanical used in storage protection. In this issue, the bioassay was carried out on Sitophilus zeamais to assess the effectiveness of binary combinations of Hymenocardia acida wood ash and Plectranthus glandulosus leaf powder regarding adult toxicity, progeny inhibition, and reduction of damage and germination ability. Plectranthus glandulosus leaf powder, H. acida wood ash and their binary combinations significantly induced mortality of S. zeamais adult (P? 0.0001). The higher mortality rate was achieved by the highest content (40 g/kg) of H. acida wood ash (94.66%) and 25PG75HA (94.59%) within 14 days of exposure. The combinations of P. glandulosus leaf powder with H. acida at different proportions produced different interactions. The combination made up by 75% of P. glandulosus leaf powder with 25% of H. acida wood ash produced synergistic effect whereas that made up by 50% of each of two powders had antagonistic effect in weevil mortality. The three combinations of H. acida and P. glandulosus significantly reduced the progeny production. In term of inhibition of F1, the combination 25PG75HA revealed more effective than the two other. The grain damage and population increase were significantly reduced. In general, the non-infested maize grain had a good germination rate than the infested ones. The treatments did not have negative effect on seed germination. From These results, the two powders and their binary combinations could be used to reduce grain infestation by insect while taking in account the proportions of insecticidal powders implied in the combination.