Studies on the critical water mass, rehydration capability and potential, acute chill tolerance and supercooling point of Argas (Persicargas) walkerae (Acari: Argasidae).
The critical water mass, defined as the water mass remaining in a dehydrated tick in the non-ambulatory state, differed only slightly between light and heavy mass groups of Argas walkerae and averaged 23.6% and 23.2%, respectively, in males and 28.4% and 28.0%, respectively, in females. All ticks survived dehydration to 50%, 75% or 100% of their critical water mass, and 95% of them rehydrated during their subsequent incubation at 95% relative humidity (RH) and 28 degrees C for 14 days and regained their ambulatory status. Unfed adults were able to balance water loss frequently over a period of several months. When ticks were repeatedly dehydrated at 0% RH for 14 days, females and males suffered 50% mortality after 16 and 19 cycles of de- and rehydration, respectively, over a period of 278 days and 337 days, respectively. Water itself was not attractive to either dehydrated or non-dehydrated ticks and drinking was not observed. After submergence in water for 3 days, most of the dehydrated adult ticks gained mass. Judged by 50% mortality, larvae tolerated short-term extreme chilling to -24 degrees C, nymphs 1 to -22 degrees C, nymphs II to -20 degrees C, females and males to -19 degrees C. None survived tissue freezing. At a chilling rate of 0.3 degrees C/min, mean supercooling points (SCP) ranged from -25.9 degrees C in eggs to -16.5 degrees C in unfed females. The SCP of all other stages was significantly higher than that of eggs. Mean SCPs of unfed adult ticks dehydrated to 50% or 75% of their critical water mass were significantly lower than that of fully hydrated ticks. The SCPs of ticks acclimated by several weeks exposure to 0 degrees C or to 38 degrees C were significantly lower than those of adult ticks kept constantly at 28 degrees C.
Stark
U
U
Institute for Comparative Tropical Medicine and Parasitology, University of Munich, Germany.
Gothe
R
R
D000818:Animals; D003080:Cold Temperature; D003681:Dehydration; D005260:Female; D008297:Male; D016019:Survival Analysis; D013987:Ticks / Q000502:physiology*; D013997:Time Factors; D014867:Water
D014867:Water