title: Activity studies of sesquiterpene oxides and sulfides from the plant Hyptis suaveolens (Lamiaceae) and its repellency on Ixodes ricinus (Acari: Ixodidae).
abstract: Hyptis suaveolens (Lamiaceae), a plant traditionally used as a mosquito repellent, has been investigated for repellent properties against nymphs of the tick Ixodes ricinus. Essential oils and volatile compounds of fresh and dried leaves, from plants originating from Laos and Guinea-Bissau, were identified by GC-MS and tested in a tick repellency bioassay. All the essential oils were strongly repellent against the ticks, even though the main volatile constituents differed in their proportions of potentially tick repellent chemicals. (+)/(-)-sabinene were present in high amounts in all preparations, and dominated the emission from dry and fresh leaves together with 1,8-cineol and α-phellandrene. 1,8-Cineol and sabinene were major compounds in the essential oils from H. suaveolens from Laos. Main compounds in H. suaveolens from Guinea-Bissau were (-)-sabinene, limonene and terpinolene. Among the sesquiterpene hydrocarbons identified, α-humulene exhibited strong tick repellency (96.8 %). Structure activity studies of oxidation or sulfidation products of germacrene D, α-humulene and β-caryophyllene, showed increased tick repellent activity: of mint sulfide (59.4 %), humulene-6,7-oxide (94.5 %) and caryophyllene-6,7-oxide (96.9 %). The substitution of oxygen with sulfur slightly lowered the repellency. The effects of the constituents in the oils can then be regarded as a trade off between the subsequently lower volatility of the sesquiterpene derivatives compared to the monoterpenes and may thus increase their potential usefulness as tick repellents.
authors.affiliation: Department of Bioenviroment, Faculty of Agriculture, Yamagata University, 1-23 Wakaba-Machi, Tsuruoka, Yamagata, 997-8555, Japan.|Ecological Chemistry Group, Department of Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Ashitani
authors.affiliation: Medical Entomology Unit, Department of Systematic Biology, Evolutionary Biology Centre (EBC), Uppsala University, SE-752 36, Uppsala, Sweden.
authors.forename: S S
authors.initials: SS
authors.lastname: Garboui
authors.affiliation: Ecological Chemistry Group, Department of Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology, SE-100 44, Stockholm, Sweden. fredrikschubert@hotmail.com.
authors.forename: F
authors.initials: F
authors.lastname: Schubert
authors.affiliation: Ecological Chemistry Group, Department of Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.|National University of Laos (NOUL), Vientiane, Laos.
authors.forename: C
authors.initials: C
authors.lastname: Vongsombath
authors.affiliation: Section of Organic Chemistry, Institute of Technology, 50411, Tartu, Estonia.
authors.forename: I
authors.initials: I
authors.lastname: Liblikas
authors.affiliation: Ecological Chemistry Group, Department of Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Pålsson
authors.affiliation: Ecological Chemistry Group, Department of Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology, SE-100 44, Stockholm, Sweden.|Section of Organic Chemistry, Institute of Technology, 50411, Tartu, Estonia.
authors.forename: A-K
authors.initials: AK
authors.lastname: Borg-Karlson
mesh_terms: D056810:Acaricides; D000818:Animals; D008401:Gas Chromatography-Mass Spectrometry; D006169:Guinea-Bissau; D031331:Hyptis / Q000737:chemistry*; D018884:Ixodes; D007812:Laos; D009822:Oils, Volatile; D010087:Oxides; D010936:Plant Extracts / Q000737:chemistry; D018515:Plant Leaves / Q000737:chemistry; D012717:Sesquiterpenes; D013440:Sulfides; D013983:Tick Control
chemical_list: D056810:Acaricides; D009822:Oils, Volatile; D010087:Oxides; D010936:Plant Extracts; D012717:Sesquiterpenes; D013440:Sulfides
keywords: Caryophyllene oxide; Caryophyllene sulfide; Essential oil; Hyptis suaveolens; Ixodes ricinus; Repellency