Gynandropsis gynandra essential oil and its constituents as tick (Rhipicephalus appendiculatus) repellents

The repellency of the essential oil of the previously reported anti-tick pa sture shrub Gynandropsis gynandra and identified constituents of the oil we re evaluated against the livestock tick, Rhipicephalus appendiculatus. In a tick-climbing repellency bioassay, the oil of G. gynandra exhibited a repe llency effect which at the highest treatment levels was higher than that of the commercial arthropod repellent N,N-diethyltoluamide. Twenty eight comp ounds were identified in the G. gynandra oil by GC, GC-MS and coinjection w ith authentic samples. Carvacrol was found to occur in largest quantity (29 .2%), followed by trans-phytol (24.0%), linalool (13.3%), trans-2-methylcyc lopentanol (7.2%) and beta-caryophyllene (4.4%). m-Cymene, nonanal, 1-alpha -terpineol, beta-cyclocitral, nerol, trans-geraniol, carvacrol, beta-ionone , trans-geranylacetone and nerolidol were the most repellent components aga inst R. appendiculatus. Methyl isothiocyanate which occurred in the G. gyna ndra oil at a relative percentage of 2.1 and which was not tested in the bi oassay due to its toxicity may also contribute significantly to the repelle ncy of the oil. The repellency of the oil of G. gynandra supported earlier findings by other workers that G. gynandra repelled R. appendiculatus ticks . (C) 1998 Elsevier Science Ltd. All rights reserved.