On the nature of pre-freeze mortality in insects: water balance, ion homeostasis and energy charge in the adults of Pyrrhocoris apterus
2004
SUMMARY Three acclimation groups [i.e. non-diapause (LD), diapause (SD) and
diapause, cold-acclimated (SDA)] of the adult bugs Pyrrhocoris
apterus differed markedly in their levels of chill tolerance. Survival
time at a sub-zero, but non-freezing, temperature of –5°C (Lt50)
extended from 7.6 days, through 35.6 days, to >60 days in the LD, SD and
SDA insects, respectively. The time necessary for recovery after chill-coma
increased linearly with the increasing time of exposure to –5°C, and
the steepness of the slope of linear regression decreased in the order
LD>SD>SDA. The capacity to prevent/counteract leakage of
Na + down the electrochemical gradient (from haemolymph to
tissues) during the exposure to –5°C increased in the order
LDchill-tolerant insects (LD) showed the highest rate of
body-water loss. Most of the water was lost from the haemolymph compartment.
The ability to regulate a certain fraction of ion pools into the hindgut fluid
was the highest in the SDA group, medium in the SD group and missing in the LD
group. The adenylate energy charge in the fat body cells was constant in all
three groups. The total pools of ATP, ADP and AMP, however, decreased in the
SD and SDA groups but remained constant in the LD group. The inability of
insects to maintain ion gradients at sub-zero temperature is discussed as an
important cause of pre-freeze mortality.
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