Water Relations of the Ticks Rhipicephalus Appendiculatus Neumann, 1901 and Rhipicephalus Pulchellus Gerstacker, 1873

Abstract

Fully hydrated, newly moulted, unfed nymphs and adults of Rhipicephalus pendiculatus and R. pulchellus were exposed to . controlled relative humidities (RH) of 0%, 20%, 33%, 55%, 62%, 75%, 85% and 96% at 18°c, 23°c, 27 0 C and 310 c. Changes in weight of individual adults and nymphs, determined at regular intervals in batches of 50, resulted from water loss and water gain were found to be balanced near 85% RH, which is therefore t he critical equilibrium humidity (CEH ) . It was found that the weight changes were independent of temperature. Longevity was shortened at RHs below the CEH and water loss .was most rapid at 33%, 20% and 0% RHs and was therefore the limiting factor to their survival. Mortality curves were constructed for each humidity. They showed an LD50 at 0% RH of about 6.5 days for female R. pendiculatus 6.8 days for female R.~lche llus and about 9.4 days for males of the two species. Water vapour uptake from a near saturated atmosphere was studied using males and females of both. species , and covering various parts of the body with paraffin wax (M.P . 44-45°c). It was.shown that mouth-parts are major site of water vapour uptake. Invesitigation of the lipid content of unfed - adults of both species showed that lipid reserves were insufficient on oxidation to provide enough water to contribute significantly to replacing water losses. Cuticular permeability in both live and dead ticks at different rates of desiccation showed a curvilinear relationship to temperature. Females showed significantly greater water losses than males' of the same. species . Between species, R.pulchellus females consistently showed ,. a significantly lower rate of water loss than R.appendiculatus females. These findings help in explaining the distribution of the two species in nature, where R. pulchellus shows a preference for markedly arid habitats compared to R. appendiculatus.