Identification of Larvicidal Constituents of the Essential Oil of Echinops grijsii Roots against the Three Species of Mosquitoes

The screening of Chinese medicinal herbs for insecticidal principles showed that the essential oil ofEchinops grijsiiHance 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%) andcis-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 ofE. grijsiiexhibited larvicidal activity against the fourth instar larvae ofAedes albopictus,Anopheles sinensisandCulex pipiens pallenswith LC50values 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 ofAe. albopictus(LC50= 0.34 μg/mL and 0.45 μg/mL, respectively) andAn. sinensis(LC50= 1.36 μg/mL and 5.36 μg/mL, respectively). The two isolated thiophenes also had LC50values against the fourth instar larvae ofC. pipiens pallensof 0.12 μg/mL and 0.33 μg/mL, respectively. The findings indicated that the essential oil ofE. grijsiiroots and the isolated thiophenes have an excellent potential for use in the control ofAe. albopictus,An. sinensisandC. pipiens pallenslarvae and could be used in the search for new, safer and more effective natural compounds as larvicides.Keywords:Echinops grijsii;Aedes albopictus;Anopheles sinensis;Culex pipiens pallens;larvicidal activity