Evaluation of common cocklebur Xanthium strumarium leaf extract as post-harvest grain protectant of black gram against pulse beetle Callosobruchus chinensis (Coleoptera: Bruchidae) and isolation of crude compound

The pulse beetle Callosobruchus chinensisL. is considered the most important stored grain pest of black gram Vigna mungoHepper in Bangladesh and other tropical and subtropical countries. Bioactive compounds derived from plants can be used to control of the pulse beetle as a potential alternative to synthetic insecticides. Therefore, aqueous extracts of common cocklebur Xanthium strumariumL. leaf was examined for insecticidal properties against C.chinensis. The extracts showed toxicity, repellent properties, inhibited fecundity and adult emergence of the insects, and protected grains. Insect mortality was accounted highest (72.6%) with 4% extract at 4 days after treatment. The beetles showed highest repellency rate (58.0%) with 4% concentration at 1 hour exposure; however insect repellency decreased with time. The beetles exerted the lowest fecundity and grain damage and produced the lowest number of offspring when they were reared on grains treated with 4% extract. The insecticidal compounds present in common cocklebur leaf were extracted in chloroform and ethanol, and isolated by thin layer chromatography (TLC) and spectral studies (¹H-NMR and IR), which identified the presence of aromatic ester, n-hexyl salicylate or o-hydroxy-n-hexyl-benzoate and a long-chain ketone. Therefore, naturally occurring X.strumarium and its derivatives may be potential components for integrated management of C.chinensis.