Abstract

Chill tolerance (time of survival at -5°C) increased in non-diapausing (reproducing) adults of Pyrrhocoris apterus after a gradual, 4-week-long decrease in ambient temperature from 25° to 0°C. The level of chill tolerance attained after cold-acclimation was considerably lower than that in similarly cold-acclimated diapausing adults. Some physiological changes accompanied the cold-acclimation, irrespective of developmental state (diapause vs. reproduction). They were: A decreased oxygen consumption, loss of body water, an increased haemolymph osmolality, an increased proportion of phosphatidylethanolamines vs. a decreased proportion of phosphatidylcholines in membrane phospholipids, and an increased proportion of linoleic vs. a decreased proportion of oleic acid in phosphatidylethanolamines. Such changes could contribute to the limited potential for cold-acclimation found in non-diapausing insects. Other physiological changes appeared to require the induction of diapause prior to cold-acclimation. They were: Down regulation of ice nucleators resulting in a lowering of the individual supercooling point, synthesis and accumulation of specific winter polyols, an increased proportion of palmitic acid in membrane phospholipids; and regulation of the concentrations of Na+ and K+ in the haemolymph. The potential contributions of these changes to the cold hardiness of P. apterus are discussed.

Highlights

  • It is accepted widely that mechanisms of insect cold hardiness are numerous, diverse, often speciesspecific and work in integration (Baust & Rojas, 1985; Lee & Denlinger, 1991; Danks, 1996; Somme, 1999; 2000)

  • The photoperiodic induction of diapause and/or exposure to low temperatures results in a restructuring of the phos­ pholipid composition of the biological membranes of P. apterus, which may contribute to cold hardiness (Hodkováetal., 1999)

  • In this study we show that the level of chill tolerance is much lower in non-diapausing individuals of P. apterus than in diapausing individuals

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Summary

Introduction

It is accepted widely that mechanisms of insect cold hardiness are numerous, diverse, often speciesspecific and work in integration (Baust & Rojas, 1985; Lee & Denlinger, 1991; Danks, 1996; Somme, 1999; 2000). Their mean supercooling point (SCP, approximately -13°C) is about 4°C lower than that of non-diapausing adults and may decrease further to a minimum of between -16° and -21°C upon exposure to declining, but still relatively high, ambient temperatures above 5°C (Hodková & Hodek, 1997; Košťál & Šimek, 2000).

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