SUMMARY Adults of the insect Pyrrhocoris apterus acquire chill tolerance through the process of autumnal acclimatization. Field and laboratory experiments were conducted to separate the triggering effects of low temperatures, desiccation and diapause progression on the physiological characteristics related to chill tolerance with emphasis on the restructuring of glycerophospholipid (GPL) composition. Changes in relative proportions of major molecular species of glycerophosphoethanolamines (GPEtns) and glycerophosphocholines (GPChols) in thoracic muscle and fat body tissues were followed using HPLC coupled to electrospray ionisation mass spectrometry. The increase in relative proportion of 1-palmitoyl-2-linoleyl-sn-GPEtn at the expense of 1,2-dilinoleyl-sn-GPChol was the most prominent feature of the complex change observed in both tissues during autumnal acclimatization in the field. The relative proportion of total GPEtns increased, while the proportion of total GPChols decreased. The relative proportion of unsaturated fatty acyls slightly decreased. A similar restructuring response was seen during acclimatization in the field and cold acclimation in the laboratory. By contrast, the GPL changes related to desiccation and diapause progression were relatively small, differed qualitatively from the cold-acclimation response, and were accompanied with no increase of chill tolerance. Other features of autumnal acclimatization, i.e. depression of supercooling capacity and accumulation of polyhydric alcohols,were also triggered solely by low temperatures.

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Abstract.  Diapausing adults of the red firebug, Pyrrhocoris apterus, were maintained in the laboratory at constant conditions of 20 °C and short days (LD 12 : 12 h) for 5 months. Spontaneous termination of diapause is seen in 0.4% of adults. At different times of diapause development, groups of adults were exposed to an 8‐week gradual cold treatment ending at 0 °C. Ribitol and sorbitol contents remain very low at constant 20 °C and their rapid accumulation only occurrs at temperatures below 5 °C. The capacity to accumulate ribitol in response to low temperature stimulus remains relatively stable but the capacity to accumulate sorbitol decreases to zero during the 5 months of diapause development. Glycogen (whole‐body and fat‐body reserves) accumulates relatively rapidly during the early phase (up to 1–2 months) and slowly depletes during the late phase of diapause development under constant conditions. Upon cold treatment, part of the glycogen reserve was depleted. The activities of most enzymes involved in polyol metabolism (namely glycogen phosphorylase, glucose‐6‐P dehydrogenase, phosphofructokinase, aldose reductase, polyol dehydrogenase and ketose reductase) increase relatively rapidly during the early phase of diapause development and, in the late phase, they either become stable or slowly decrease. Cold treatment has either no effect or results in a moderate increase in activity when applied in the early phase of diapause development but results in a more or less obvious decrease of enzymatic activity when applied in the late phase.

The earthworm, Dendrobaena octaedra, is a common species in the uppermost soil and humus layers of coniferous forests and tundra in temperate and subarctic regions. The species is freeze-tolerant and may survive several months in a frozen state. Upon freezing, glycogen reserves are rapidly converted to glucose serving as a cryoprotectant and fuel for metabolism. In the present study we investigated the induction of freeze-tolerance under field conditions, and sought to find relationships between temperature, glycogen and fat reserves, membrane phospholipid composition and the degree of freeze-tolerance. Freeze-tolerance was induced when worms had experienced temperatures below 5 degrees C for 2 weeks or more. Freeze-tolerance was linked to the magnitude of glycogen reserves, which also fluctuated with field temperatures being highest in autumn and winter. On the other hand fat reserves seemed not to be linked with freeze-tolerance at all. However, high glycogen alone did not confer freeze-tolerance; alterations in the membrane phospholipid fatty acid composition (PLFA) were also necessary in order to secure freeze-tolerance. The changes in PLFA composition were generally similar to changes occurring in other ectothermic animals during winter acclimation with an increased degree of unsaturation of the PLFAs.

Abstract. The activities of three enzymes involved in polyol biosynthesis (aldose reductase, AR; ketose reductase, KR; and polyol dehydrogenase, PDH) were studied in adult females of the linden bug, Pyrrhocoris apterus, collected from the field during 2005/2006. While the activities of three enzymes were low in reproductive females, activities greater by one or two orders were seen in reproductively arrested females. AR and KR showed similar seasonal trends in activity. Activities were low during diapause initation and later increased and stabilized during autumnal diapause development. Further increases of AR and KR activities were seen during low temperature quiescence and finally the activities sharply decreased during vernal resumption of direct development. The activity of PDH was relatively high (but fluctuating) during diapause, then decreased in quiescent insects and almost disapeared in reproductively active females. Insects collected in February were subjected to laboratory de-acclimation (exposure to high temperatures) followed by re-acclimation (exposure to low temperatures) which resulted in loss of activity in all three enzymes and no regain. High activities of AR, KR and PDH in reproductively arrested females thus conform well with their previously observed high capacity to synthesize and accumulate polyol cryoprotectants.