Ecology of mountain pine beetle (Coleoptera : Scolytidae) cold hardening in the intermountain west

The mountain pine beetle, Dendroctonus ponderosae Hopkins, spends the major ity of its life cycle within the phloem of pine trees, experiencing exposur e to temperatures below -30 degrees C in many parts of their expansive rang e. To better understand cold tolerance capabilities of this insect, seasona l patterns of cold-hardiness, as measured by supercooling points in the lab oratory, were compared with seasonal patterns of host tree phloem temperatu res at several geographic sites for 2 beetle generations. Larvae were found to be intolerant of tissue freezing, and supercooling points measured appe ar to be a reasonable estimate of the lower limit for survival. Of the comp ounds analyzed, glycerol was found to be the major cryoprotectant. No diffe rences in supercooling points were found among instars or between larvae co llected from the north and south aspect of tree boles. Both phloem temperat ures and supercooling points of larvae collected from within the phloem wer e found to be different among the geographic sites sampled. Mountain pine b eetle larvae appear to respond to seasonal and yearly fluctuations in micro habitat temperatures by adjusting levels of cold hardening.