Abstract

A study was carried out on the insecticidal effects of the powdered stem bark extract of Uvaria chamae and its ethanolic extract on three most devastating stored products pests (Coleopterous) in Nigeria, namely: Callosobruchus maculatus F. (Bruchidae), Rhizopertha dominica F. (Bostrichidae) and Sitophilus zeamais Motschulsky (Curculionidae). Graded concentrations of each formulation of the powdered bark and ethanolic extracts were in exposure chambers of each insect in laboratory bio-assays under ambient conditions (25±2°C). S. zeamais, R. dominica and C. maculatus were exposed to the following concentrations 0.00, 0.10, 0.20, 0.40, 0.80, and 1.60 mg/L grains in three replicates per treatment and control. The mortality of the insects was used to compute mean lethal concentration (LC₅₀) values by probit analysis. All the concentrations tested showed appreciable toxicity against each test insect species. The computed LC₅₀ values for powder formulation gave significantly (P≤0.05) higher toxicity against C. maculatus (1.281 g/kg) than either S. zeamais (2.145 g/kg) or R. dominica (5.189 g/kg). However, the ethanolic extract was more toxic on C. maculatus (0.134 mL/L), S. zeamais (0.173 mL/L) or R. dominica (0.359 mL/L). It was found that the higher the concentration of the ethanolic extract, the higher the mortality. The result implies that, U. chamae powdered and ethanolic stem bark extracts have potentials for use during storage of grains, ensuring food security, profit maximization and availability of seeds for the next planting season without being damaged by these test insect species. The presence of high concentration of steroids and terpenes may be responsible for the observed high insecticidal activity of the test extracts.

Key words: Bioassay, Callosobrochus maculatus, storage insect, Uvaria chamae.