Abstract
To find a new and safe alternative to conventional insecticides, we evaluated the fumigant toxicity of eight Lamiaceae essential oils and their constituents against the adult rice weevil Sitophilus oryzae. Of the eight species tested, hyssop (Hyssopus offcinalis), majoram (Origanum majorana), and Thymus zygis essential oils showed strong fumigant toxicity against S. oryzae adults at 25 mg/L air concentration. Constituents of active essential oils were analyzed by gas chromatography coupled to flame ionization detector (FID) and gas chromatography-mass spectrometry. A total of 13, 15, and 17 compounds were identified from hyssop, majoram, and Thymus zygis essential oils, respectively. Pinocamphone and isopinocamphone were isolated by open column chromatography. Among the test compounds, pinocamphone and isopinocamphone showed the strongest fumigant toxicity against S. oryzae. Sabinene hydrate, linalool, α-terpineol, and terpinen-4-ol exhibited 100% fumigant toxicity against S. oryzae at 3.9 mg/L air concentration. The measured toxicity of the artificial blends of the constituents identified in hyssop, majoram, and Thymus zygis oils indicated that isopinocamphone, terpine-4-ol, and linalool were major contributors to the fumigant toxicity of the artificial blend, respectively.
Highlights
IntroductionSeveral synthetic pesticides, including organophosphate, pyrethroids, or gaseous pesticides, have been widely used for the control of rice weevils [2]
The rice weevil, Sitophilus oryzae (L.) is a serious insect pest of stored cereals around the world [1].Several synthetic pesticides, including organophosphate, pyrethroids, or gaseous pesticides, have been widely used for the control of rice weevils [2]
We evaluated the fumigant toxicity of eight Lamiaceae plant essential oils and their constituents against the rice weevil S. oryzae to find new alternatives for conventional pesticides
Summary
Several synthetic pesticides, including organophosphate, pyrethroids, or gaseous pesticides, have been widely used for the control of rice weevils [2]. They could be obtained by steam distillation and contain many bioactive compounds with fumigant toxicity against insect pests of stored cereals [1,2,3,4,5]. Another advantage of plant essential oils and their constituents is high volatility [6,7,8]. The high volatility of plant essential oils and their constituents reduces concern for their residues on stored grains
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