Attractants of the Brown Ear Tick, Rhipicephalus Appendiculatus, Found in Cow Ear Washes

Abstract

The brown ear tick, Rhipicephalus appendiculatus, is a very important tick species in Africa since it is the vector of Theileria parva, the protozoan that causes East Coast Fever (ECF), in cattle. ECF is usually a fatal disease with a mortality rate of 90% and over. In animals that survive, productivity is reduced, weight loss is marked and the hide is damaged. Tick-borne diseases have conventionally been controlled by acaricides, but these imported chemicals are generally too expensive for third world countries. Alternative methods of tick control are therefore a dire necessity. Modern methods of control seek to utilise semiochemicals or their synthetic analogues in the manipulation of pest populations by modifying arthropod behaviour or disrupting normal physiological processes ofthe same. ln this study, the chemical cues suspected to be present on the ear pinna, which is the predilection site for the adult R. appendiculalus were collected. A comparison between two solvents used for this collection revealed that methanol was more superior to hexane. Hexane was however preferentially used because of its ease of evaporation. When comparing bioassay responses of whole samples tested against females and males, it was clearly evident that the ticks were attracted to some component(s) in the sample. The female ticks registered higher readings than the male at all dose applications and were subsequently used. The extracts were separated into basic (Fraction S), neutral (Fraction R), acidic (Fraction Q) and phenolic / enolic (P) fractions. Bioassays that were carried out using each of these fractions revealed attractancy only in Fraction P. V The compounds in this fraction were analysed by gas chromatography and electron impact mass spectrometry. El-MS spectra were used to tentatively identify compounds by comparison with NIST/NBS mass spectral library of standards. Confirmation of this identification was then achieved by retention time comparison of authentics as well as peak area enhancement by co-injection with commercially available synthetic standards. The compounds identified from Fraction P were phenol, 2-hydroxybenzaldehyde, 4-methylphenol, 4-hexen-3-one, 4-ethylphenol and .3-ethylphenol. Ofthese compounds, the authentic samples ofthe last two were bioassayed against female ticks at (loses of 0.0001, 0.001, 0.01, 0.1, 1.0, 10.0 and 100.0 pg per application but failed to show any attractancy. The other three phenolics are compounds that have been documented severally in the past as attractants of this tick. It is no wonder therefore that the inner ear of the cow pinna_ a site that contains phenol, 4-methylphenol and 2-hydroxybenzaldehyde should be attractive to the brown ear tick, R. appendiculalus. The potential of using these kairomones for tick control, which res0urce—po0r farmers in third world countries need to reduce costs on imported commercial acaricides, is highlighted.