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First published online March 22, 2004
Journal of Experimental Biology 207, 1509-1521 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00923

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On the nature of pre-freeze mortality in insects: water balance, ion homeostasis and energy charge in the adults of Pyrrhocoris apterus

V. Kotál^1,*, J. Vambera² and J. Bastl³

¹ Institute of Entomology, Academy of Sciences, eské Budjovice, Czech Republic
² Faculty of Biological Sciences, University of South Bohemia, eské Budjovice, Czech Republic
³ Agricultural Faculty, University of South Bohemia, eské Budjovice, Czech Republic

^* Author for correspondence (e-mail: kostal{at}entu.cas.cz)

Accepted 4 February 2004

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 LD<SD<SDA. As a result, the rates of counteractive outward movement of K⁺, and of the E_K dissipation, decreased in the same order. The least chill-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.

Key words: chill tolerance, diapause, water loss, ion gradient, pre-freeze mortality, Heteroptera, Pyrrhocoris apterus

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