The influence of freeze duration on postfreeze recovery by caterpillars of Pyrrharctia isabella (Lepidoptera: Arctiidae): when is survival enough to qualify as recovery?

J Exp Zool A Comp Exp Biol. 2006 Jul 1;305(7):570-5. doi: 10.1002/jez.a.300.


The effects of freeze exposure at -4.5 degrees C for as long as 6 weeks on long-term postfreeze survival and body fluid composition were investigated in caterpillars (woolly bears) of the arctiid moth Pyrrharctia isabella. Woolly bears routinely survived the initial postfreeze period with little difference between the 1-week (100%) and 6-week (95%) freeze treatments. Caterpillars in the latter treatment, however, reached the pupal stage almost one half as often as woolly bears in the 1-week freeze treatment. The success rate for adult emergence was not different for pupae from the two treatments (ca. 50%). Woolly bears responded to cold acclimation by accumulating glycerol to levels exceeding 300 mM although this was not augmented by extending the acclimation period to 6 weeks. There was a significant (P<0.05) rise in hemolymph [K+] during the first week of the freeze (23.4-37.8 mM), which then remained stable over the remainder of the 6-week freeze period. Hemolymph [Na+] did not change from the prefreeze level over the course of the freeze treatment. Body water content showed a modest rise during the course of the freeze treatment but the underlying cause for this change was uncertain. Prolonged freeze exposure had a major impact on long-term survival of the woolly bears but this was not reflected by any instability in body fluid composition. Moreover, short-term recovery was not an effective indicator of the tolerance of P. isabella caterpillars to prolonged freezing.

MeSH terms

  • Adaptation, Physiological
  • Animals
  • Cryoprotective Agents / analysis
  • Freezing
  • Hemolymph / chemistry
  • Larva / physiology
  • Longevity
  • Moths / growth & development*
  • Moths / physiology*
  • Pupa / physiology
  • Seasons
  • Survival Analysis
  • Time Factors


  • Cryoprotective Agents