Repellency of Plant Essential Oils to Key Coleopteran Stored Grain Insects of Rice

Laboratory studies were conducted to assess the repellant effects of three essential oils from plants viz., orange, eucalyptus and cinnamon oils against four major coleopteran stored grain insect pests of rice viz., Sitophilus oryzae, Oryzaephilus surinamensis, Rhyzopertha dominica, and Tribolium castaneum. The % repellency (PR) and index of repellency (RI) were observed to range from 10 to 100% and 0.00 to 0.90, respectively. Eucalyptus oil @ 5% showed maximum repellent action against Tribolium castaneum, registering PR and RI values of 93.33 (F=0.921), 100 (F=1.66), 100 (F=3.772) and 0.07, 0.00 and 0.00, respectively at 3, 6 and 12 hrs after treatment and were found significantly superior over rest of the treatments. Chemical profiling of tested oils through GCMS showed presence of 2- 3 chemical constituents amounting to >90 % of total composition of oil. The results highlight the repellency effects of the essential oils and indicate that these can be ecofriendly ones for the post-harvest protection of rice.