Characterization of Cattle Anal Odour Blend Responsible for Repellency against Rhipicephalus Appendiculatus, the Vector of East Coast Fever
Kariuki, Margaret Wangechi
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East Coast fever (ECF) is one of the most devastating livestock diseases in east, central and southern Africa, and remains the major health hindrance to the development and improvement of the livestock industry. Although synthetic chemical acaricides have made a tremendous impact over the years in the control and management of the vectors on livestock, ticks have developed resistance to most of them In addition, these chemicals are toxic to non-target organisms. Previous on-host behavior studies of adult R. appendiculatus showed preference to feed mainly inside and around the ear of their hosts. Combination of a repellent blend from the anal region and attractive blend at the ear has been sho-wn to play natural "push" and "pull" roles, respectively, to guide these ticks to the cattle ears. The present study aimed at characterizing and evaluating the constituents and blend in cattle anal odour responsible for repelling adults of brown ear tick. The anal odours, and for comparison, odours emanating from fresh dung were analyzed by gas chromatography-linked mass spectrometry (GC-MS). The individual constituents were identified by comparing their mass spectra with those in the National Institute of Standards and Technology (NIST) libraries. The major constituents of the anal odour were diisobutylphthalate (41.27%), o-xylene (9.2%), 4-hydroxy-4-methyl-2- pentanone (4.6%), 4-methyl-2-methoxyphenol (4.3%), ethyl benzene (2.7%), 2,6,6- trimethyl-[IS(la,~,5a)]bicycloheptanes (0.6%), 5-ethoxydihydro-2(3H)-furanone (0.5%), 3-methylene-2-pentanone, (0.5%), 5-methyl-2-phenyl-1H-indole (0.4%), and 3-pentanone (0.2%). Three compounds namely 4-hydroxy-4-methyl-2-pentanone, N- (3-methyl-l-oxobutyl)-alanine methyl ester and 2,4-dimethyl-benzo[h ]quinoline) were common in both anal and dung odours. The repellency of odours, selected constituents, blends and DEET was evaluated using two choice climbing assay. The anal and fresh dung odour had comparable repellence (RD50 2.7 and 2.9, respectively). Of the individual compounds tested, 4-methyl-2-methoxyphenol was found to be most repellent (RD75 =0.56) while 3-pentanone was least active (RD75 = 622.7). The two blends evaluated were more repellent than the anal and dung odours. One of the blends (made up of 4-methyl-2-methoxyphenol, 3-pentanone, 3-methyl-2- pentanone, and 4-hydroxy-4-methyl-2-pentanone) tested gave RD75 of 0.032. The other blend (without 3-pentanone) was more repellent (RD75= 0.019; P ::S 0.05, SNK). In addition, of the analogues tested, 2,4-dimethylphenol was most repellent (RD75= 0.0089) while 3,4-methylenedioxytoluene was inactive. The study lays down the groundwork for characterizing compounds and/or blends with potent repellence against the Brown Ear Tick on cattle.