Studies on the critical water mass and the rehydration potential of unfed adult Dermacentor marginatus and D. reticulatus ticks (Acari: Ixodidae).

In unfed adult Dermacentor marginatus and D. reticulatus ticks survival and capability to restore water balance after loss of high percentages of exchangeable body water were investigated. Furthermore, it was examined how frequently dehydrated ticks of these species were able to rehydrate by uptake of atmospheric water vapour. The critical water mass, defined as the water mass remaining in a tick at the nonambulatory state, differed between light and heavy weight groups and averaged 62.4 and 55.8%, respectively, of the total body water of fully hydrated ticks in females, and 54.4 and 51.1%, respectively, in males of D. marginatus. In D. reticulatus, the corresponding figures were 55.9 and 54.7% in females and 52.1 and 52.7% in males. All ticks survived dehydration to 50, 75 or 100% of the critical water mass, and 96.7% of the D. marginatus ticks and 95.8% of the D. reticulatus ticks compensated water losses during subsequent incubation at 95% relative humidity (r.h.) and 20 degrees C. Unfed females and males of both Dermacentor spp. were capable to balance water loss very frequently over a period of several months. When ticks were repeatedly dehydrated at 0% r.h. for 7 days and rehydrated at 95% r.h. and 20 degrees C, females and males of D. marginatus reached the 50% mortality after 22 and 29 cycles of de- and rehydration, respectively, during 211 and 285 days, respectively. In D. reticulatus, 50% of females and males survived 23 and 17 cycles, respectively, during 248 and 186 days, respectively. Rehydration weights were as high or even higher as those of ticks kept at permanent 95% r.h.

Studies on survival and water balance of unfed adult Dermacentor marginatus and D. reticulatus ticks (Acari: Ixodidae).

The water content, the survival time at various relative humidities (r.h.) and the critical equilibrium activity of unfed adult Dermacentor marginatus and D. reticulatus ticks were investigated at a constant temperature of 20 degrees C. It was also examined whether these ticks use liquid water to compensate water loss. Both Dermacentor spp. showed no significant differences in water content in relation to body mass. The mean water content of D. marginatus and D. reticulatus was 54.6% and 54.7%, respectively, in females and 56.3% and 57.0%, respectively, in males. The survival time of unfed adults prolonged with decreasing saturation deficits. On average, males survived longer than females and D. marginatus ticks survived mostly longer than D. reticulatus ticks. The 50% mortality period ranged between 40 d at 33% r.h. and 420 d at 95% r.h. in D. marginatus, and between 43 d at 33 r.h. and 366 d at 95% r.h. in D. reticulatus. The critical equilibrium activity of unfed adults was estimated to be 0.84 for both species and was independent of sex. When dehydrated adult D. marginatus and D. reticulatus ticks were offered liquid water, only a few slightly gained weight while most further lost weight. Liquid water was not attractive for dehydrated or non-dehydrated ticks and drinking was not observed. After submerging in water for 2 d, most of the dehydrated ticks had gained weight.