MANAGEMENT OF MAIZE WEEVIL, Sitophilus zeamais (MOTSCH.) (CURCULIONIDAE: COLEOPTERA) BY WEED EXTRACTS AND A CHEMICAL INSECTICIDE

Abstract

The study was conducted to evaluate the efficacy of five indigenous weed extracts, viz. water hyacinth (Eichhornia crassipes), swamp smartweed (Polygonum coccineum), ariach (Cassia tora), wild capsicum (Croton bonplandianum) and hill glory bower (Clerodendrum viscosum) in hexane solvent and an insecticide lambda cyhalothrin for their toxicity, residual and repellent effects against the maize weevil, Sitophilus zeamais Motsch. (Curculionidae: Coleoptera) in the laboratories of the department of Entomology, HSTU, during May to December 2017. The 4 concentrations of weed extracts (0.5, 1.0, 2.0 and 3.0 % w/v) and 3 concentrations of lambda cyhalothrin (0.01, 0.1 and 0.2% w/v) along with a control were applied in bioassay. The results indicated that all the weed extracts had toxic, residual and repellent effect on maize weevil in storage. Among the weed extracts, the highest toxicity (53.33±7.90%) was found in wild capsicum whereas hill glory bower showed the lowest (21.35±4.59%). The order of the toxicity of the weed extracts were found as wild capsicum > swamp smartweed > water hyacinth > ariach > hill glory bower. Mortality percentages were directly proportional to the concentration level and hours after treatment (HAT). On the other hand the highest average mortality (84.44±2.94%) was found at the maximum concentration (0.2%) of lambda cyhalothrin but the lowest (54.44±4.84%) at the lower concentration (0.01%). All weed extracts showed good protection of maize seeds by reducing adult emergence and seed damage over control. Based on the adult emergence and seed damage the wild capsicum showed the highest residual toxicity whereas lambda cyhalothrin possessed 100% inhibition of adult emergence and seed damage. Hill glory bower showed the highest repellency (41.50±5.39%) while swamp smartweed was the lowest (26.33±5.84%). On the basis of repellency class, hill glory bower was in the repellency class III but the other extracts were in class II. In case of lambda cyhalothrin the mean repellency (41.33±4.81%) was found at 0.1% concentration of class III. Considering the toxic and residual effects, wild capsicum and for repellent effect bhat extracts were more effective against maize weevil. Beside this, lambda cyhalothrin was highly effective in showing toxic, residual and repellent effects against maize weevil