Feeding and respiratory gas exchange in the American dog tick, Dermacentor variabilis

This study investigated the effect of blood feeding on respiratory gas exchange in the dog tick Dermacentor variabilis. Adult male and female ticks were fed on bovine hosts from 1 to 11days. Females fed slowly for the first 6days and then rapidly engorged on blood 2-3days prior to dropping from the host. Ticks were removed at daily intervals during feeding, weighed and CO(2) emission measured at 25 degrees C using flow-through respirometry. During feeding, females (N=39) showed a 100-fold gain in mass from 5.78+/-1.05mg to 541.15+/-18.60mg while standard metabolic rate (Vdot;co(2)) increased from 0.179+/-0.030&mgr;lh(-1) in unfed ticks to 87.32+/-5.72&mgr;lh(-1) in fully engorged ticks. CO(2) release prior to feeding was highly discontinuous with discrete spiracular bursts of CO(2) emission approximately every 30min. For CO(2) emission measured in detached partially or completely fed ticks, burst frequency became more and more rapid as feeding progressed and changed to continuous sustained CO(2) output during rapid engorgement. In contrast to females, male ticks (N=20) showed little change in mass and maintained discontinuous CO(2) throughout the 11day attachment period on the host. The switch from discontinuous to continuous CO(2) release and presumed increase in respiratory water loss in female ticks is correlated to an increase in metabolic expenditure associated with blood meal digestion rather than any factor relating directly to maintenance of water balance.