The supercooling ability of ticks (Acari, Ixodoidea).

The supercooling capacity of nine laboratory-held species of ticks originating from different geographical areas, as well as five field-collected species from Germany, was investigated. All but one tick species showed mean supercooling points between about -17 and -23 degrees C, suggesting that the capacity to supercool to temperatures of < or = -17 degrees C might be an inherent property of many tick species unrelated to their geographic origin. Photoperiod did not influence the mean supercooling point in any of the species and there was also no distinct seasonal pattern of supercooling in seasonally acclimatized Dermacentor marginatus. Thus, the supercooling ability was independent of the presence/absence of diapause. The finding of thermal hysteresis in D. marginatus hemolymph raises the question of whether or not anti-freeze proteins are involved in the supercooling capacity of that species. An interspecies comparison revealed a weak negative correlation between relative water content and supercooling point of the ticks and an even weaker correlation between body mass or body water mass and the supercooling point. Since the ticks exhibited low supercooling points both before and shortly after feeding, the blood used as food should lack potent ice nucleators.