Exp Appl Acarol. 2015 Sep 18. [Epub ahead of print]
Activity studies of sesquiterpene oxides and sulfides from the plant Hyptis suaveolens (Lamiaceae) and its repellency on Ixodes ricinus (Acari: Ixodidae).
Ashitani T1,2, Garboui SS3, Schubert F4, Vongsombath C2,5, Liblikas I6, Pålsson K2, Borg-Karlson AK2,6.
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.
