THE SUPERCOOLING ABILITY OF TICKS (ACARI, IXODOIDEA)

The supercooling capacity of nine laboratory-held species of ticks ori ginating from different geographical areas, as well as five field-coll ected 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 less th an or equal to - 17 degrees C might be an inherent property of many ti ck species unrelated to their geographic origin. Photoperiod did not i nfluence the mean supercooling point in any of the species and there w as also no distinct seasonal pattern of supercooling in seasonally acc limatized Dermacentor marginatus. Thus, the supercooling ability was i ndependent 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 c orrelation between relative water content and supercooling point of th e ticks and an even weaker correlation between body mass or body water mass and the supercooling point. Since the ticks exhibited low superc ooling points both before and shortly after feeding, the blood used as food should lack potent ice nucleators.