Abstract
The screening of Chinese medicinal herbs for insecticidal principles showed that the essential oil of Echinops grijsii Hance roots possessed significant larvicidal activity against mosquitoes. The essential oil was extracted via hydrodistillation and its constituents were determined by gas chromatography-mass spectrometry (GC-MS) analysis. GC-MS analyses revealed the presence of 31 components, with 5-(3-buten-1-yn-1-yl)-2,2′-bithiophene (5-BBT, 27.63%), α-terthienyl (α-T, 14.95%), 1,8-cineole (5.56%) and cis-β-ocimene (5.01%) being the four major constituents. Based bioactivity-directed chromatographic separation of the essential oil led to the isolation of 5-BBT, 5-(4-isovaleroyloxybut-1-ynyl)-2,2′-bithiophene (5-IBT) and α-T as active compounds. The essential oil of E. grijsii exhibited larvicidal activity against the fourth instar larvae of Aedes albopictus, Anopheles sinensis and Culex pipiens pallens with LC50 values of 2.65 μg/mL, 3.43 μg/mL and 1.47 μg/mL, respectively. The isolated thiophenes, 5-BBT and 5-IBT, possessed strong larvicidal activity against the fourth instar larvae of Ae. albopictus (LC50 = 0.34 μg/mL and 0.45 μg/mL, respectively) and An. sinensis (LC50 = 1.36 μg/mL and 5.36 μg/mL, respectively). The two isolated thiophenes also had LC50 values against the fourth instar larvae of C. pipiens pallens of 0.12 μg/mL and 0.33 μg/mL, respectively. The findings indicated that the essential oil of E. grijsii roots and the isolated thiophenes have an excellent potential for use in the control of Ae. albopictus, An. sinensis and C. pipiens pallens larvae and could be used in the search for new, safer and more effective natural compounds as larvicides.
Highlights
IntroductionMosquitoes are carriers, or vectors, for some of humanity’s most deadly illnesses, and they are public enemy number one in the fight against global infectious disease
Beyond the nuisance factor, mosquitoes are carriers, or vectors, for some of humanity’s most deadly illnesses, and they are public enemy number one in the fight against global infectious disease.Mosquito-borne diseases cause millions of deaths worldwide every year with a disproportionate effect on children and the elderly in developing countries [1]
The yield of yellow essential oil of E. grijsii roots was 0.46% (v/w based on dry weight) while its density was measured to be 0.92 g/mL
Summary
Mosquitoes are carriers, or vectors, for some of humanity’s most deadly illnesses, and they are public enemy number one in the fight against global infectious disease. Mosquito-borne diseases cause millions of deaths worldwide every year with a disproportionate effect on children and the elderly in developing countries [1]. The common house mosquito (C. pipiens pallens) is the major vector of wuchereriasis and epidemic encephalitis B, which cause millions of deaths every year, especially in India and Africa [3,4,5]. There is a critical need for the development of alternatives to synthetic insecticides Essential oils and their constituents have been recommended as alternative sources for insect control, predominantly because some are selective, biodegrade to nontoxic products, and have minimal impacts on non-target organisms and the environment [6]. A literature survey has shown that there is no report on larvicidal activity of the essential oil of E. grijsii roots against mosquitoes, we decided to investigate larvicidal activity of the essential oil against the three mosquitoes and isolate any active constituent compounds from the essential oil using bioactivity directed fractionation
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