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 20degreesC. 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.