Cold-hardiness of a laboratory colony of lone star ticks.

Abstract

The cold-hardiness of a lone star tick, Ambylomma americium (L.) laboratory colony was characterized. Fed and unfed larvae, fed and unfed nymphs, and unfed adults did not survive exposure to -17C for 7 d. After an 8-d exposure to -10C, adults tolerated cold better than immatures and unfed specimens fared better than fed ticks. Exposing unfed 6-wk old (post mold) adult males and females to -15C for increasing intervals up to 2 hrs suggests that males were more tolerant to cold then were females. Half of all adults were alive 3 d after the 2-h low-temperature treatment. Males may have survived because of a significantly higher hemolymph osmotic pressure, although the solute concentration increased for both sexes after a 2-h exposure to 0C. Acclimation to 5C for 7 d had no influence on supercooling points for unfed males and females, engorged nymphs and larvae, and eggs. None of the life stages survived supercooling, which strongly suggests that this species is freeze-intolerant. Intolerance of immature stages to chilling may be a limiting factor in the northern distribution of lone star ticks in North America.