Effects of Insecticidal Efficacy of Securidaca longepedunculata (Polygalaceae) Powder Root Bark Extracts Against Sitophilus zeamais (Curculionidae) for Pest Control in the far North Region of Cameroon

Currently, farmers are misusing synthetic pesticides to control stored food pests. These pesticides have harmful effects both for the consumers and for the environment. When harvesting their cereals, some farmers use several methods to reduce pest pressure during storage. This study investigated the use of powdered formulations of the bark of Securidaca longepedunculata combined with the fruit mantis of Acacia nilotica against Sitophilus zeamais. For this purpose, a granulometric study of powder particles was performed to determine the sieve mesh intervals in order to obtain different powdery extracts. These extracts, at varying proportions, were each used to formulate bioinsecticides that were assessed with respect to insecticidal activity on the different developmental stages of S. zeamais. Furthermore, an acute toxicity study of the most promising aqueous extract was carried out on rats. The granulometric particles size analysis permitted selection of the particle size between 400 and 100 µm. The findings of the qualitative characterization of the secondary metabolites from the different fractions showed the presence of total polyphenols, flavonoids, tannins, alkaloids and saponins. Each formulated fraction at different doses (3, 5 and 8 g/kg) resulted in mortality rates (60, 80 and 90%) that were higher than that of the negative control (without S. longepedunculata powder, 5.2%) but lower than positive control (treated with the reference pesticide, 100%) at a significant difference of (P < 0.05). The insecticidal activity was dose-dependent and time-dependent. The large particles induced lower mortality compared to the small particles. However, the 8 g/kg dose of the 100 and 200 µm fraction resulted in higher mortality rates (86.2-90%) during the experimental periods (5, 35 and 90 days). No clinical signs of toxicity or mortality of rats, as well as no changes in body weight, were observed with S. longepedunculata root bark aqueous extract at a dose of 2000 mg/kg. This study suggests the potential use of the formulated powder from the roots of S. longepedunculata as an alternative to synthetic insecticides in the fight against S. zeamais. Key words: Securidaca longepedunculata, Acacia nilotica, Sitophilus zeamais, synthetic pesticides, toxicity