Inhibitory, reductive, and repellent activities of hexane, acetone, and methanol extracts from Plectranthus glandulosus leaves against Callosobruchus maculatus

Abstract

This study evaluates the inhibitory, reductive, and repellent activities of hexane, acetone, and methanol extracts from the leaves of Plectranthus glandulosus against Callosobruchus maculatus, a pest of cowpea. The extracts were obtained through fractionation and tested for their effectiveness in reducing the population growth of C. maculatus and the mass loss of seeds. After 7 days of infestation, dead insects were removed and the living ones reintroduced. The seeds were kept in the laboratory until the total emergence of the first progeny. To evaluate damage and losses, the seeds were stored for three months. A linear olfactometer was used for the repellency test. The results show that the extracts inhibited the growth of C. maculatus and significantly reduced their populations. At a dose of 5 g/kg, a reduction of 100±0.00% in the progeny of C. maculatus was observed. The hexane, acetone, and methanol extracts achieved 100%, 84.41±2.31%, and 80.11±2.11% reduction of the F1 progeny of C. maculatus, respectively, with the dose of 5 g/kg. Hexane extracts were particularly effective, inducing class V repellency at a dose of 10 g/kg. Extracts from P. glandulosus can be used as natural insecticides for crop protection, particularly cowpea, due to their secondary metabolites possessing proven inhibitory and repellent properties at low doses.