COLD-HARDINESS OF A LABORATORY COLONY OF LONE STAR TICKS (ACARI, IXODIDAE)

The cold-hardiness of a lone star tick, Amblyomma americanum (L.), lab oratory colony was characterized. Fed and unfed larvae, fed and unfed nymphs, and unfed adults did not survive exposure to -17 degrees C for 7 d. After an 8-d exposure to -10 degrees C, adults tolerated cold be tter than immatures and unfed specimens fared better than fed ticks. E xposing unfed 6-wk-old (postmolt) adult males and females to -15 degre es C for increasing intervals up to 2 h suggests that males were more tolerant to cold than were females. Half of all adults were alive 3 d after the 2-h low-temperature treatment. Males may have survived becau se of a significantly higher hemolymph osmotic pressure, although the solute concentration increased for both sexes after a 2h exposure to 0 degrees C. Acclimation to 5 degrees C for 7 d had no influence on sup ercooling points for unfed males and females, engorged nymphs and larv ae, and eggs. None of the life stages survived supercooling, which str ongly suggests that this species is freeze intolerant. Intolerance of immature stages to chilling may be a limiting factor in tile northern distribution of lone star ticks in North America.