ISOLATION AND CHARACTERIZATION OF THE INSECTICIDAL FRACTION FROM LEAF EXTRACTS OF Tithonia diversifolia A. Gray

Abstract

The different fractions of the acetone extract of Tithonia diversifolia A. Gray leaves were separated by preparative layer chromatography after precipitation of pigments and more polar constituents with lead acetate. The insecticidal fraction was identified through insect bio-assay using Dysdercus cingulatus Fab., Tribolium castaneum Herbsr. and Sitophilus zeamais Motsch. The median lethal dose (LD50) of the active fraction was obtained for these species and for Plutella xylostella L. and Spodoptera exempta Walker. The toxicity of the semi-purified isolate was only 24.47% less toxic (LD50 = 1.3657 mg/g) than malathion (LD50 = 1.0972 mg/g) to P. xylostella, but was much less toxic than the said insecticide to the other test species. The toxicity of the isolate to P. xylostella was comparable with values obtained for synthetic insecticides used for this insect. Characterization of the active fraction suggested the presence of a gamma-lactone with a hydroxyl group attached to the ring or to an alkyl substituent. Unsaturation may be present in the ring itself, or external to the ring, alpha to the carbonyl.