CHOLESTERYL ESTERS ON THE BODY SURFACES OF THE CAMEL TICK, HYALOMMA-DROMEDARII (KOCH, 1844) AND THE BROWN DOG TICK, RHIPICEPHALUS-SANGUINEUS (LATREILLE, 1806)

Cholesteryl esters were found to constitute a major component of the l ipids coating the body cuticle of females of the camel tick, Hyalomma dromedarii and the brown dog tick, Rhipicephalus sanguineus. One or mo re cholesteryl esters, alone or in combination, have been shown to ser ve as the mounting sex pheromone of several species of ixodid ticks. C onsequently, knowledge of these compounds is important for an understa nding of the mating behavior of these ticks. Based on thin layer chrom atography, cholesterol and cholesteryl esters were the most abundant n eutral lipids found on the body surfaces of fed females of these two s pecies. Analysis using HPLC demonstrated significant quantities of the following compounds, tentatively identified as cholesteryl esters (ex pressed in micrograms per female equivalent), in H. dromedarii: Choles teryl acetate 18.2; cholesteryl laurate, 6.8; cholesteryl linoleate, 2 4.8; cholesteryl oleate, 12.9; cholesteryl palmitate, 0.3; and cholest eryl stearate 1.7. In contrast, the same method revealed only 3 choles teryl esters in extracts of females of R. sanguineus: Cholesteryl acet ate, 2.0; cholesteryl linoleate, 8.5; and cholesteryl oleate, 3.0. In both species, two unidentified peaks, with the spectral characteristic s of cholesteryl esters, were also observed. Identification of the cho lesteryl esters was confirmed: by (1) positive bioassay results with c onspecific (H. dromedarii) males and heterospecific (Dermacentor varia bilis) males: (2) similarity of ultraviolet spectra between identified sample peaks and authentic standards: and (3) demonstration of choles terol and the corresponding free fatty acid following enzymatic digest ion of each of the HPLC-separated fractions containing the different c holesteryl esters. Comparisons with the cholesteryl ester composition of the mounting sex pheromone of other metastriate Ixodidae are discus sed. These findings, along with studies reported previously, suggest t hat differences in the mounting sex pheromones of ixodid ticks are an important factor in minimizing heterospecific matings in nature.