Abstract
The essential oil of Stachys riederi var. japonica (Family: Lamiaceae) was extracted by hydrodistillation and determined by GC and GC-MS. A total of 40 components were identified, representing 96.01% of the total oil composition. The major compounds in the essential oil were acetanisole (15.43%), anisole (9.43%), 1,8-cineole (8.07%), geraniol (7.89%), eugenol (4.54%), caryophyllene oxide (4.47%), caryophyllene (4.21%) and linalool (4.07%). Five active constituents (acetanisole, anisole, 1,8-cineole, eugenol and geraniol) were identified by bioactivity-directed fractionation. The essential oil possessed fumigant toxicity against maize weevils (Sitophilus zeamais) and booklice (Liposcelis bostrychophila), with LC50 values of 15.0 mg/L and 0.7 mg/L, respectively. Eugenol and anisole exhibited stronger fumigant toxicity than the oil against booklice. 1,8-Cineole showed stronger toxicity, and anisole as well as eugenol exhibited the same level of fumigant toxicity as the essential oil against maize weevils. The essential oil also exhibited contact toxicity against S. zeamais adults and L. bostrychophila, with LC50 values of 21.8 µg/adult and 287.0 µg/cm2, respectively. The results indicated that the essential oil of S. riederi var. japonica and its isolates show potential as fumigants, and for their contact toxicity against grain storage insects.
Highlights
Maize weevil (Sitophilus zeamais Motsch.) has a nearly cosmopolitan distribution
Monoterpenoids represented 19 of the 40 compounds, corresponding to 41.18% of the whole oil, while 15 of the 40 constituents were sesquiterpenoids (23.86% of the crude essential oil). This is the first documentation of the chemical composition of the essential oil of S. riederi var. japonica aerial parts
The results are quite different from several essential oils derived from Stachys species, which is found in China
Summary
Maize weevil (Sitophilus zeamais Motsch.) has a nearly cosmopolitan distribution. Occurring throughout the warmer parts of the world, it is one of the most destructive primary insect pests of stored cereals [1]. Repeated use of those fumigants/insecticides for decades has led to resurgence of stored-product insect pests, sometimes resulting in the development of resistance [8,9]. Japonica) is a perennial, rhizomatous herb distributed only in some areas of China (e.g., Anhui, Fujian, Hebei, Henan, Jiangsu, Jiangxi, Liaoning, Inner Mongol, Shandong, and Zhejiang province), and Russia and Japan. It is distributed in wet areas of ravines and riverbanks, and was used in Chinese traditional medicine for tonsillitis, sore throats, and dysentery [13]. This paper deals with the isolation and structure determination of bioactive constituents from the essential oil, as well as their insecticidal activities
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