Die isolering en identifisering van die hondafwerende faktor in die kutikulêre afskeiding van die geelhondebosluis, Haemaphysalis leachi

[摘要] ENGLISH ABSTRACT:When in close contact with the Yellow Dog Tick, Haemaphysalis leachi, dogs showclear signs of disgust or even nausea. It is accepted that the secretion is produced bythe tick in order to prevent the dog from removing the tick from its body with itsteeth, thereby increasing the chances for the tick's survival.The composition of this secretion was studied in order to identify the chemicalcompounds responsible for the repellent action of the secretion.Because of the dog's keen sense of smell, the tick only needs to produce minutequantities of this repellant, which significantly complicated the detection of thedifferent components by conventional GC-methods. Several sampling and sampleenrichment methods were explored, including solvent extraction, SPME sampleenrichment, adsorption on active charcoal, cryoprecipitation, sorption in a phasecoatedopen tubular trap, as well as solventless sampling, in order to determine whichmethod would ensure an appropriate amount of sample for gas chromatographicdetection.Two of these sampling methods yielded acceptable results: The first method consistedof rinsing irritated female ticks with dichloromethane and, after concentrating thesample by evaporation, GC-MS analysis using normal splitless injection. The secondmethod entailed collecting secretions by wiping irritated ticks with glass micro fibrefilter paper after which the paper was inserted directly into the inlet liner of the GCMSsystem, where thermal desorption of the volatile constituents of the secretionpreceded gas chromatographic separation and mass spectral detection.Live dogs were needed for the evaluation of the isolated material to determinewhether the samples had an aversive effect on them. The extract was separated intodifferent fractions, which were further separated into subfractions. After eachseparation process, all the fractions were tested for efficacy in order to determinewhich fraction contained the active components, narrowing down the number of candidate target compounds. It was concluded that a combination of aldehydes,namely hexanal, heptanal, octanal, nonanal, decanal, undecanal and dodecanal, isresponsible for the dog repelling action of the secretion.In most cases the semiochemicals of insects and mammals are secreted in a morecomplex matrix to ensure prolonged activity. For this reason some of the othercompounds in the complex cuticular secretion of this tick species were also identifiedduring the course of this study.

[发布机构] Stellenbosch University