Abstract
Experiments were carried out at the laboratory of the Entomology Division, Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh and Department of Chemistry, University of Dhaka, Dhaka, during the period from March 2010 to July 2014. The n-hexane, dichloromethane (DCM) and methanol extracts of leaf and seed/fruit of karanja, Pongamia pinnata (L.); mahogany, Swietenia mahogani Jacq.; neem, Azadirachta indica A. Juss and urmoi, Sapium indicum Willd. at 2.0, 4.0, 6.0, 8.0 and 10.0% (w/v) concentrations were evaluated for their insecticidal, repellent, antifeedant and residual effect against rice weevil, Sitophilus oryzae. Among the test plants, urmoi showed the highest toxic effect for rice weevil (mortality, 47.00%) at 72 hour after treatment (HAT). Among the solvents, dichloromethane extract showed more toxicity than other extracts. Comparing the extracts, the highest repellency was observed in urmoi extract on rice weevil (mean repellency, 53.04%). The results also showed that urmoi plant extract had the highest antifeedant effects on rice weevil having total coefficient of deterrency 126.52. Between neem seed and urmoi fruit extracts, the lowest number of F1 adult emerged (17.33), the least grain infestation rate (4.38%), and the highest inhibition rate (40.65%) was found in urmoi extract on rice grains at 20 days after treatment. The dichloromethane soluble urmoi fruit extract was fractionated by solvent-solvent partition into two parts; aqueous 90% methanol and n-hexane soluble parts. Both fractions were subjected to perform bioassay which showed insecticidal and feeding deterrent activity. The n-hexane soluble part extract showed highest mortality (100.00%) and total co-efficient of deterrency was 173.66 whereas 90% aqueous methanol part showed mortality (50.00%) and total co-efficient of deterrency was 150.89%. n-hexane soluble part on silica gel column chromatography yielded eleven fractions in varying amounts. Eleven fractions were subjected to perform bioassay which showed insecticidal and feeding deterrent activity. The HF-4 and HF-6 fractions extract showed mortality (40.00 and 50.00%, respectively) and total co-efficient of deterrency was (117.57 and 134.20, respectively). From the HF-4 and HF-6 active fractions four compounds (Ia, Ib, Ic and II) were isolated. The structures of the four active compounds were determined by FTIR, High Resolution NMR spectroscopic methods including H-H and C-H COSY, HSQC, HMBC and LC-MS\MS. Names of the isolated active compounds are Ia-Dibutyl phthalate, Ib-Butylpentyl phthalate, Ic-Dipentyl phthalate and II-[2-ethyl-4-butyl-8-methoxycarbonyl] octyl [2-ethyl-4-propyl-8-hydroxycarbonyl] octyl phthalate. These isolated compounds may be used as a source of developing botanical insecticides for insect pests.