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Summary: PHYSIOLOGICAL AND CHEMICAL ECOLOGY
Cold Tolerance of Four Species of Bark Beetle (Coleoptera:
Scolytidae) in North America
MARIŽA J. LOMBARDERO, MATTHEW P. AYRES, BRUCE D. AYRES,1
AND JOHN D. REEVE2
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755
Environ. Entomol. 29(3): 421Đ432 (2000)
ABSTRACT We investigated the overwintering biology of four temperate-latitude bark beetles:
Dendroctonus frontalis Zimmermann, Ips pini (Say), I. grandicollis (Eichhoff), and I. perroti Swaine.
All four species were freeze-susceptible. However, there was variation within and among species in
overwintering biology that related to their geographic distribution. D. frontalis and southern pop-
ulations of I. grandicollis continued to reproduce and develop under the bark of their host plants
throughout the winter and did not show any seasonal adjustments in their lower lethal temperatures:
mean supercooling point SD 12.15 4.02 and 12.25 2.50 C. In contrast, northern
populations of I. grandicollis and I. pini employ a behavioral strategy in which adults migrate to the
forest soil, where they are insulated from temperature extremes by litter and snow. Furthermore,
adult supercooling points of both northern populations declined from about 13 C in summer to
about 17 C in early winter. A concomitant decline in lipid content suggests that lipid metabolism
may be involved in seasonal adjustments of cold tolerance in I. pini. An assortment of temperature
manipulations failed to provide any evidence of cold tolerance acclimation. Immatures, which
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