Ventilation in the adults of Amblyomma hebraeum and A. marmoreum (Acarina, Ixodidae), vectors of heartwater in Southern Africa

Abstract

The objective of this study was to establish the major features of respiratory gas exchange in unfed adults of the ticks Amblyomma hebraeum and A. marmoreum, both vectors of heartwater in Southern Africa. Carbon dioxide emission of ticks was measured at 25 °C using flow-through respirometry in order to determine standard metabolic rate (SMR) and the temporal pattern of gaseous emission. For both species, SMR was extremely low and approximately 100 fold less than that predicted for an insect of equivalent body mass. Ventilation in inactive ticks was discontinuous and characterized by periodic bursts of CO₂ emissions during spiracular opening. The main selective advantage of this type of ventilation is believed to lie in a reduction of respiratory water loss. The periodicity of CO₂ bursts was less frequent in A. marmoreum (every 2.5 h) compared to A. hebraeum (every1.5 h) suggesting that A. marmoreum is more efficient at conserving respiratory water loss. It is suggested that future research into water balance physiology of ticks should address the role of ventilatory patterns in determining off-host survival and habitat associations.