INSECTICIDAL POTENCY OF SOME INDIGENOUS PLANT EXTRACTS AGAINST RICE WEEVIL, Sitophilus oryzae (L.) (CURCULIONIDAE: COLEOPTERA)

Abstract

Experiments were conducted to study the bioefficacy of some indigenous plant extracts against rice weevil, Sitophilus oryzae L. in the laboratory of the Department of Entomology, Hajee Moharnimad Danesh Science and Technology University (HSTU), Dinajpur during the period from April to October 2012. The petroleum ether —" of seed of ata (Annona reticulata) and castor (Ricinus communis), leaf of karabi (Nerium olender), marigold (Calendula officinalis) and nishinda (Vitex negundo) at 0.5, 1.0 and 1.5 % concentration were evaluated for their repellent, direct toxic and residual effects against rice weevil. The results showed that all five plants extracts were effective in checking insect infestation and had different toxic, residual and repellent effects against rice weevil. Among the tested plant extracts, ata seed extract showed the highest toxic effect (64.18 % mortality) and lowest number of F1 adult (7.75 %) emergence but castor seed extract showed the lowest toxic effect (21.66 % mortality) and highest number of F1 adult (18.08 %) emergence. Mortality percentage was also found directly proportional to the level of concentrations of plant extracts and to the exposure period. The repellent effect of ata, castor, karabi, nisinda and marigold extracts showed that the five plant extracts had moderate repellent action on rice weevil. Ata seed extract also showed the highest repellency (49.45 %) while castor seed extract provided the lowest repellency (33.62 %). Residual effect of ata seed extract was also higher than all other plant extracts. Considering all the concentration and efficacy, the order of toxicity of plant extracts was ata » karabi » marigold » nishinda >» castor.