Abstract

Laboratory studies were conducted to study the effect of plant powders and acetonic extracts of four plants species Ruta chalepensis L., Eupatorium adenophorum (Spreng.)King & H.Rob., Ocimum sanctum L. and Zingiber officinale Rosc. against rice weevil, Sitophilus oryzae L (Coleoptera Curculionidae) infesting paddy grains. Among them, leaf powders of E. adenophorum, O. sanctum and R. chalepensis @ 5 g per 25 g of seeds, were significantly superior with cent percent adult mortality on 14 days after treatment . Insecticidal activity of acetonic extracts of the plants was assessed by seed treatment method, filter paper diffusion method (direct contact application) and fumigation methods. The insect responses towards the treatment depended on the type of plant, the time of exposure and the mode of application. Among them acetonic extracts of E. adenophorum, and R. chalepensis @ 3 % v/w were effective with cent percent adult mortality 3 days after treatment. E. adenophorum, and R. chalepensis @ 2 % also recorded cent percent adult mortality on 5 and 7 days after treatment, respectively, whereas O. sanctum @ 3 % recorded 100 percent mortality on 7 days after treatment. In a test with the filter paper diffusion method, E. adenophorum leaf extract showed 100% mortality within three days after treatment at 8.5 mg /cm, whereas, only 88.67% mortality was observed in R. chalepensis, 65.89% in Z. officinale and 61.67 % in O. sanctum at this dosage. E. adenophorum leaf extract having volatile toxic chemicals as indicated by 43.00 per cent adult mortality in fumigation bioassays.

Keywords: Ruta chalepensis, Eupatorium adenophorum, Ocimum sanctum, Zingiber officinale, Sitophilus oryzae, botanical insecticides