Mechanism and Characteristics of Coxal Fluid Excretion in the Argasid Tick Ornithodorus Moubata

Adult ticks (Omithodorus moubata Murray, Acari, Argasidae) were fed on human blood at 37 °C in a beaker covered with chicken skin. 14C-labelled inulin and 3–0[14CH3]glucose were rapidly cleared from haemolymph to coxal fluid ; the coxal tubule appeared not to reabsorb either substance. Glucose was reabsorbed from tubular fluid via a phlorrhizin-sensitive mechanism. Reabsorption of amino acids varied between o and 90 % but was greatest for those amino acids which were scarce in the meal. During normal feeding conditions, there was positive correlation between haemocoelic hydrostatic pressure and rate of coxal fluid excretion. Unilateral cannulation of a coxal organ so as to eliminate back pressure of a valve at the coxal orifice led to a twofold increase in rate of coxal fluid production compared to the contralateral side. The above data confirm that coxal fluid excretion occurs by a filtration resorption mechanism.