Evaluation of Ricinus communis Extracts as a Biopesticide for Nisotra gemella Control

The efficacy of the extracts of leaves of castor (Ricinus communis) on flea beetle (Nisotra gemella), ravaging sorrel (Hibiscus sabdariffa), was performed in the laboratory of Phytochemistry of the Faculty of Sciences (Loyola University of Congo). The insects were captured on the leaves of Hibiscus sabdariffa in the field using plastic jars.

Toxicity tests were conducted in laboratory conditions in Petri dishes at a temperature of 28 ± 1°C. The results of the preliminary toxicity test of the total extracts showed a mortality of 100% for the petroleum ether extracts, 31.33% for the ethanolic extract, and 0% for the total aqueous extract, after 24 hours of exposure. The petroleum ether extracts was chosen for further investigations.

Different concentrations of the total petroleum ether extract were applied on filter paper (1%: 0.53 ml / cm²; 0.1%: 0.05 ml / cm²; 0.05%: 0.03 ml / cm²) caused 100% mortality for the dose of 0.53 ml / cm² in the interval of 9 and 10 hours; 0.05 ml / cm² caused 100% mortality after 15 -16 hours. An interval of 19 to 20 hours was necessary to cause 100 % mortality using the concentration of 0.03 ml / cm². No mortality was recorded in control plates (petroleum ether).

The same doses were used to evaluate the repellent effect. It was observed a low insect activity with an average rate of 39.5%. The thin layer chromatography enabled the identification of 10 spots (petroleum ether and ethyl acetate/ 5:1) and 8 spots (Petroleum ether and ethyl acetate/ 9:1).