International Journal of Agriculture and Medicinal Plants Volume 1(1): 16-25, 2020 To cite this article: Sultana A, Bachchu MAA, Ara R, Bhuyain MMH and Moniruzzaman M. 2020. Comparative toxicity study of leaf, bark and stem extracts of eucalyptus against Sitophilus oryzae L. (Curculionidae: Coleoptera). Intl. J. Agric. Med. Plants. 1(1): 16-25. Comparative toxicity study of leaf, bark and stem extracts of eucalyptus against Sitophilus oryzae L. (Curculionidae: Coleoptera) Ayrin Sultana, Md Adnan Al Bachchu*, Roushan Ara, Mohammad Mosharof Hossain Bhuyain and Md Moniruzzaman 1 Department of Entomology, Hajee Mohammad Danesh Science and Technology University, Dinajpur 5200, 1 Department of Agricultutre, Fulbari Womans College, Dinajpur, Bangladesh. Research article Article history Received: 27.09.2020 Accepted: 20.12.2020 Published: Online: 31.12.2020 *Corresponding author: adnan@hstu.ac.bd www.isciencepub.com ABSTRACT Comparative toxicity of the extract of eucalyptus leaf, bark and stem as a botanical insecticides against rice weevil, Sitophilus oryzae L., the most common and destructive insect in all types of rice storage in Bangladesh, was evaluated based on toxicity, repellency and residual activity in the laboratory conditions (28±3°C and 70±5% RH). The extract was prepared with methanoic solvents and applied in four doses (0.5, 1.0, 1.5 and 2.0%) with control. Extracts from all three parts had toxic effects against rice weevil but the extracts of the eucalyptus stems showed the highest (mortality, 34.53%) toxic effect while extract of leaves showed the lowest (mortality, 11.20%) effect. The lower LD50 values of the stem extract also showed the highest toxic effects against rice weevils. In the residual toxicity test, the stem extract also showed the lowest number of adult emergence (36.53) and the highest percent of infestation inhibition (67.42%), but the highest number of adult emergence was recorded in the control (78.33) treatment. Among the tested plant parts of eucalyptus, the stem extract showed the highest repellent effect (73.33%) and the leaves extract was the lowest (56.33%). All levels of extract had direct toxicity, residual and repellent effects, but the highest response was obtained using 2.0% and the toxicity increased in proportion to the level of concentration. Considering the toxicity, residual and repellency effects, toxicity were found in the order of stem>bark>leaf. We therefore, suggest that the stem extract of eucalyptus are promising for environment friendly management practices against stored grain pests. Keywords: Eucalyptus, residual toxicity, repellency effect, Sitophilus oryzae L. INTRODUCTION More than 600 species of Coleopteran pests attack stored products which cause quantitative and qualitative losses (Rajendran and Sriranjini 2008). Among the stored product pests, the rice weevil, Sitophilus oryzae L. (Coleoptera: Curculionidae) are the common and most destructive pest of the stored raw cereal grains in the world. Such types of insects are very active in warm and humid areas especially in Bangladesh. It is well known that both the adults and grubs are serious pests of stored grains and stored products such as rice, wheat, maize, sorghum, barley, lentil, biscuits, dried potatoes, cornflower, beans, pumpkin seeds, millets, etc (Hanies 1991). Infestation with the rice weevil also indirectly quality loss the grains by the encourage of mould growth and growth of other insect populations (Rees 2004). The estimated damage caused by these pests measured about 5 to 10 % in the temperate zone and 20 to 30 % in the tropical zone (Haque et al. 2000). To reduce the loss of grains in stores due to this notorious pest, rice weevil and other important stored product pests, several of devices, principles, and management practices are taken by the people of many