Insecticidal activity of (2n-octylcycloprop-1-enyl)-octanoic acid (I) against three Coleopteran stored product insects from Sterculia foetida (L.)

Abstract

The insecticidal activities of the extracts, fractions, and pure compound of Sterculia foetida (L.) seeds were investigated against three major stored product pests, namely, Sitophilus oryzae (L.), Callosobruchus chinensis (L.), and Tribolium castaneum (H.), through contact and fumigation bioassay. Responses varied with test chemicals, insect species, exposure times, and doses individually. The biologically active constituent of the S. foetida seeds was characterized as a cyclopropene fatty acid structurally elucidated as (2n-octylcycloprop-1-enyl)-octanoic acid (I) by spectroscopic analysis. The filter paper application of, (2n-octylcycloprop-1-enyl)-octanoic acid (I) at 0.2 mg/cm² caused 100% mortality to all test insects 2 days after treatment (2 DAT). Among the chromatographic fractions, only the pure hexane-eluted fraction caused 100% mortality at 0.3 mg/cm² to S. oryzae and C. chinensis 2 DAT, while the dose required to obtain the same percentage of mortality with the crude seed extract was 0.6 mg/cm². Under all treatment conditions, T. castaneum exhibited less susceptibility, taking longer than the other insects to show symptoms of toxicity. In terms of fumigant activity, the compounds appeared to be more effective in a vapor form against all the three insects in closed containers compared with open containers. These results suggest that the insecticidal activities of the test compounds were attributable to contact mode of action, although there was also significant fumigant toxicity. The results indicate that the bioactive compound isolated from S. foetida could act as a potent insecticide against S. oryzae, C. chinensis, and T. castaneum populations.