Reproduction Retardant and Fumigant Properties in Essential Oils Against Rice Weevil (Coleoptera: Curculionidae) in Stored Wheat

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Abstract
Thirty-one naturally occurring essential oils of plant origin (1,000 ppm in acetone) were studied under laboratory conditions for reproduction retardant, fumigant toxicity, and grain protection capability against Sitophilus oryzae (L.). The volatile oil obtained from Pinus longifolia Roxburgh reduced the population of S. oryzae 37.51, 75.21, and 86.82% compared with controls of 30, 60, and 90 d after application, indicating the strong reproduction retardant property of the oil. In contrast, essential oils from Callicarpa macrophylla Vahl and Zanthoxylum alatum Roxburgh increased the insect population 1.5 and 2 times more than controls in 90 d, respectively; these oils showed significant growth promotion. Only Mentha citrate Ehrhart oil showed significant fumigant toxicity when applied to stored wheat grain. However, this effect lasted for only 30 d. Amomum subulatum Roxburgh, Artemisia maritime L., Cedrus deodara (Roxburgh) Loudon, and Z. alatum oils (30 d) and P. longifolia oil (60 d) protected wheat grains from damage. None of the oils, however, could protect wheat grain from damage throughout the entire study period (90 d). The lowest grain damage was observed when seeds were treated with P. longifolia and Cymbopogon winterianus Jowitt oils. Isolation of active principles from these biologically active essential oils may be a new natural source of insect control agents.