Physiology of cold-acclimation in non-diapausing adults of Pyrrhocoris apterus (Heteroptera)

Abstract

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 coldacclimation, 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 regu lation 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.

Photoperiod, diapause and cold-hardiness

“…Two-week exposure of non-diapause adults of P. apterus to a low temperature of +4°C resulted in 73% mortality, while all diapause individuals survived a four-week exposure to the same temperature and only 13% mortality was recorded after six weeks (Hodkova, unpubl.). The time of survival at a subzero temperature of -5°C in adults of P. apterus acclimated at warm temperature of 26°C was much longer in diapause (Lt50 = 28.6 days, ) than in non-diapause (Lt50 = 7.8 days, Slachta et al, 2002a) adults, although the SCP was lower than -5°C in both groups of insects. While cold acclimation resulted in a substantial increase in the survival at subzero temperatures in diapause adults (Lt50 at -5°C increased to > 50 days, , non-diapause adults showed only a slight increase in survival in approximately 50% of the population (Slachta et al, 2002a).…”

“…The time of survival at a subzero temperature of -5°C in adults of P. apterus acclimated at warm temperature of 26°C was much longer in diapause (Lt50 = 28.6 days, ) than in non-diapause (Lt50 = 7.8 days, Slachta et al, 2002a) adults, although the SCP was lower than -5°C in both groups of insects. While cold acclimation resulted in a substantial increase in the survival at subzero temperatures in diapause adults (Lt50 at -5°C increased to > 50 days, , non-diapause adults showed only a slight increase in survival in approximately 50% of the population (Slachta et al, 2002a). Thus, similar to the supercooling capacity, the survival at low temperatures is enhanced in two steps: (1) during the induction of diapause, (2) during cold acclimation.…”

“…Achaearanea tepidariorum (Therid., Araneae) Hodkova & Hodek, 1994Slachta et al, 2002aHodkova et al, 1999Kostal & Simek, 2000 SCC Nakata, 1998), in the braconid A. ervi, the survival of diapause mummies at -10°C was only twice as great (LT50 : 10 days vs. 5 days) (Langer & Hance, 2000). When diapause was induced in the third instar larvae of the tortricid Adoxophyes orana by short-day photoperiod at a relatively high temperature of 20°C, survival at -5°C was much higher than in non-diapause larvae reared at a long-day photoperiod at 20°C (Table 2).…”

“…In our team, we have partly followed the global trend and studied both the role of cryoprotectants (Kostal & Simek, 2000;Slachta et al, 2002a, b) and changes in phospholipids in cell membranes (Hodkova et al, 1999(Hodkova et al, , 2002Slachta et al, 2002a;Kostal et al, 2003). However, due to our earlier discovery of biphasic cold hardening in P. apterus (Hodkova et al, 1992;Hodkova & Hodek, 1994) we have continued our eco-physiological studies on cold-hardiness.…”

How insects survive the cold: molecular mechanisms—a review

“…This remodelling of cell membrane lipids in response to changes in temperature is termed homeoviscous adaptation (HVA). HVA at low temperatures has been studied in several insects: Pyrrhocoris apterus (Slachta et al 2002); Drosophila species (Ohtsu et al 1998), Eurosta solidaginis (Bennett et al 1997), Delia antiqua (Kayukawa et al 2007), Chymomyza costata (Koštál et al 2003) and Sarcophaga crassipalpis (Michaud and Denlinger, 2007). In the C. costata example the transition to diapause was accompanied by an increase in the molar proportion of molecular species containing palmitic/linoleic (16/18.2) fatty acids esterified to sn-1/sn-2 positions of glycerol.…”