Norwegian Journal of Entomology - Norsk entomologisk forening

temperatures were more fluctuating, but fell
slightly below 0 °C only once in a cold period just
before the snow appeared. Air temperatures at 8
cm above the surface frequently dropped below
0 °C from the end of September and down to -15
°C in the end of October. When the snow appeared
in the middle of October, temperatures below the
surface became stabilized at approximately 0
°C. The lowest measured temperature during the
winter was -0.7 °C. From the middle of October,
only minor differences were recorded by the three
thermocouples below the surface.
Cold hardiness
Long term survival
The beetles appeared to be highly chill tolerant.
Among adults exposed to 2 °C for 314 d, 58 %
survived (Table 1). Following feeding for four
weeks in the laboratory, 91 % of the remaining
beetles survived another exposure to 2 °C for 420
days. At –3 °C, more than 75 % of adult G. pallida
survived for 239 d (Table 1). Two-thirds of the
beetles survived for 191 d at –6 °C., while in a
sample of 12 specimens all were killed after 218
days at this temperature.
In contrast, the pupae were more susceptible to
long term exposure at low temperatures, and all of
them died during 57 d at 0 °C (Table 1).
Supercooling
The supercooling points of adult beetles collected
during the autumn and stored at 0 °C in the
laboratory, did not change significantly from
October to February (Table 2). In April the
SCPs were slightly lower than in December.
An ANOVA test did not show any significant
differences between the measurements from
October to February. Adults collected in their
reproductive phase in early June had a mean SCP
similar to those of the overwintering beetles. All
beetles were killed by freezing at temperatures
corresponding to their SCP.
The SCPs of 2. instar larvae collected from the
shrubs in July had a mean SCP within the same
range.
Table 1. Survival of adults and pupae of
Gonioctena pallida during long term exposure to
low temperatures.
Temp. Percent
°C n Days mortality
Adults
Pupae
2 46 314 42.3
23 1 420 91.3
-3 30 239 23.0
-6 12 127 0
12 191 33.3
12 218 100
0 129 57 100
1 Following feeding 4 weeks in the laboratory
Table 2. Mean supercooling points of adults and
larvae of Gonioctena pallida collected during the
summer and stored at 0 °C in the laboratory.
Stage Date n SCP±SD
Adult
Larvae
1 Tested shortly after collection
Norw. J. Entomol. 53, 5-9, 22 May 2006
June 1 12 -10.3±1.1
Oct 20 -9.7±3.2
Dec 15 -10.2±2.8
Feb 12 -9.3±3.9
Apr 11 -8.0±3.4
July 7 -9.7±1.9
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