Monoterpenes as Effective Biocides for Sitophilus oryzae Linnaeus and Lipaphis erysimi (Kalt.)

Various pure monoterpenes and essential oils, including limonene-free citrus oil (LFC), ocimene, dihydrotagetone, carvone, a-terpineol, terpenyl acetate, and linalool were tested for their toxicity and repellency against Sitophilus oryzae (rice weevil) and Lipaphis erysimi (mustard aphid). All the compounds showed varying degrees of toxicity on both the insect pests. LFC exhibited the highest repellent activity against L. erysimi (93.33%), followed by carvone (76.66%) and a-terpenyl acetate (73.33%). LFC and carvone also caused 100% aphid mortality within 12 h, with similar efficacy of linalool (90.0%) and a-terpenyl acetate (90.0%). For S. oryzae, ocimene, linalool, and dihydrotagetone produced 100% mortality after 15 days of the treatment of the stored grains. It is the first study to examine the toxicological effects of isolated pure monoterpenes, ocimene, dihydrotagetone, and a fraction of citrus oil LFC on rice weevils and mustard aphids. The strong effectiveness of LFC indicated that the insecticidal activity of citrus oil is not solely attributed to its main component, limonene; the minor compounds also play a crucial role in its insecticidal properties.. KEYWORDS :Insecticidal activity, Limonene, Lipaphis erysimi, Monoterpene, Sitophilus oryzae, Repellency