Cold Shock Resistance Research Articles

Periclase-magnesium aluminate spinel ceramics filter with excellent purification efficiency on molten steel prepared from Mg(OH)2: Effect of fused MgO content

Reticulated ceramic filters are widely used in the field of steel purification to improve the quality of steel products. In this work, periclase-magnesium aluminate spinel ceramic filters with microporous MgO coating were fabricated by using Mg(OH)2 as raw material. The effect of fused MgO content on the microstructures, mechanical properties and filtration capacity of filters on Al2O3 inclusions in molten steel was comparatively studied. The results indicate that the particle packing and liquid phase sintering cooperated to promote the formation of neck connections between microporous MgO particles, which increased the cold compressive strength and thermal shock resistance of the filters. Furthermore, the results from the immersion test in molten steel demonstrate that an appropriate amount of high-temperature liquid phase and the relatively microporous structure of filter skeleton were favorable for filters to filtrate Al2O3 inclusion in molten steel. Overall, the filter with 30 wt% fused MgO had the best comprehensive performance with a cold compressive strength of 0.68 MPa, a residual retention of cold compressive strength after three thermal shock recycles of 79.07 % and a filtration efficiency of 79.06 % in reducing the total oxygen content of the steel.

Enhanced mechanical properties of novel Al2O3-based ceramic filter by using microporous corundum-spinel and nano-Al2O3 powders

In this work, the novel Al2O3-based ceramic filter prepared by replacing dense Al2O3 raw material with microporous corundum-spinel raw material is proposed and enhanced. The effects of nano-Al2O3 powder content (0, 2.5, 5 and 7.5 wt%) on the rheological properties of the slurries, microstructures, pore characteristics and mechanical properties of the filters were investigated. When the nano-Al2O3 powder content increased from 0 to 5 wt%, the rheological properties of the slurries were optimized, resulting in a larger thickness diameter and uniform distribution of the filter skeleton. The nano-Al2O3 powder with a high reactivity accelerated the diffusion mass transfer rate of ions and increased the sintering driving force, thus promoting the development and growth of the spinel grains. It also led to the formation of more spinel neck connections between the microporous corundum-spinel particles, which enhanced the cold compressive strength and thermal shock resistance of the filters, while the pore size slightly increased due to the spinel volume expansion between the particles. When the nano-Al2O3 powder content further reached 7.5 wt%, the yield stress of the slurry increased markedly due to the agglomeration phenomenon, leading to an uneven distribution of the filter skeleton and a lower cold compressive strength of the filter. Overall, the mechanical properties of the novel Al2O3-based ceramic filters were greatly enhanced by the addition of 5 wt% nano-Al2O3 powder. The filter skeleton had a bulk density of 2.19 g/cm3 and an apparent porosity of 41.8%. The novel Al2O3-based ceramic filter also exhibited a high cold compressive strength of 2.37 MPa and an excellent thermal shock resistance. It contained a rougher surface structure compared to existing filters and has the potential for better purification efficiency on molten metal in the future.

Restructuring-diffusion mechanism of calcium alumino-titanate in CaAl12O19–MgAl2O4–Al2O3 castables

Calcium alumino-titanate (CAT), a secondary material obtained from ferrotitanium slag, was used as a hibonite source to prepare CaAl 12 O 19 –MgAl 2 O 4 –Al 2 O 3 castables. The restructuring effect of CAT aggregate was compared by replacing tabular alumina aggregates with CAT aggregates of different particle sizes. The effects of CAT particle size on cold mechanical strength and thermal shock resistance of CaAl 12 O 19 –MgAl 2 O 4 –Al 2 O 3 castables were studied. The results showed that CAT aggregates with particle size of 5–3 or 3–1 mm led to more internal cracks or pores and reduced the cold mechanical strength of the castable samples fired at 1600 °C for 3 h. The use of CAT aggregates with particle size of 1–0 mm led to the formation of a well-bonded CAT aggregate and matrix, improving the cold mechanical strength and thermal shock resistance of the castable samples fired at 1600 °C for 3 h. The enhancement mechanism of fine CAT aggregates in this process was proposed based on the sintering of the matrix–aggregate interface with the formation of Ca(Al, Mg, Ti) 12 O 19 .

Evolution of reproductive traits have no apparent life-history associated cost in populations of Drosophila melanogaster selected for cold shock resistance

BackgroundIn insect species like Drosophila melanogaster, evolution of increased resistance or evolution of particular traits under specific environmental conditions can lead to energy trade-offs with other crucial life-history traits. Adaptation to cold stress can, in principle, involve modification of reproductive traits and physiological responses. Reproductive traits carry a substantial cost; and therefore, the evolution of reproductive traits in response to cold stress could potentially lead to trade-offs with other life-history traits. We have successfully selected replicate populations of Drosophila melanogaster for increased resistance to cold shock for over 33 generations. In these populations, the ability to recover from cold shock, mate, and lay fertile eggs 24 h post cold shock is under selection. These populations have evolved a suite of reproductive traits including increased egg viability, male mating ability, and siring ability post cold shock. These populations also show elevated mating rate both with and without cold shock. In the present study, we quantified a suite of life-history related traits in these populations to assess if evolution of cold shock resistance in these populations comes at a cost of other life-history traits.ResultsTo assess life-history cost, we measured egg viability, mating frequency, longevity, lifetime fecundity, adult mortality, larva to adult development time, larvae to adults survival, and body weight in the cold shock selected populations and their controls under two treatments (a) post cold chock and (b) without cold shock. Twenty-four hours post cold shock, the selected population had significantly higher egg viability and mating frequency compared to control populations indicating that they have higher cold shock resistance. Selected populations had significantly longer pre-adult development time compared to their control populations. Females from the selected populations had higher body weight compared to their control populations. However, we did not find any significant difference between the selected and control populations in longevity, lifetime fecundity, adult mortality, larvae to adults survival, and male body weight under the cold chock or no cold shock treatments.ConclusionsThese findings suggest that cold shock selected populations have evolved higher mating frequency and egg viability. However, there is no apparent life-history associated cost with the evolution of egg viability and reproductive performances under the cold stress condition.

Research on Performance and Safety of Composite Inorganic Phase-Change Materials (NaNO3/SiO2/C) under Low-temperature Cold Shock

This article studies the cold shock resistance and safety performance of NaNO3/SiO2/C composite inorganic phase-change thermal storage materials at extremely low temperatures. A low-temperature cold shock test system is built, and the composite inorganic phase-change thermal storage materials of different raw material particle sizes are carried out through the static cold shock and dynamic cold shock at − 40, − 60, − 80 and − 196 °C. The changes in quality, volume, surface morphology phase and thermal properties of the phase-change thermal storage materials are respectively analyzed by means of characterization methods such as scale, vernier caliper, DSC, SEM, and XRD. The results show that the thermal performance of phase-change thermal storage materials with different particle sizes is only 1.97-8.89%, especially under cryogenic shock at − 196 °C. The cold shock resistance is better with the increase in particle size. The physical properties, chemical properties and thermal storage capacity of the material under impact are basically stable, and it has good cold shock resistance. The cold shock of the two methods does not affect the thermal storage function of the material and does not cause thermal energy waste, and the safety performance is better.

A comparative study on seminal attributes of Sirohi and Beetal bucks

A total of 126 ejaculates, 21 from each of six bucks comprising three Beetal and three Sirohi bucks, collected by artificial vagina were used to study various semen characteristics. The semen characteristics viz., ejaculate volume, mass activity, initial sperm motility, live sperm, sperm concentration, sperm number per ejaculate, cold shock resistance index, live intact acrosome and sperm abnormalities were studied by conventional methods. The overall mean values of different characteristics of fresh semen in Beetal and Sirohi bucks for ejaculate volume, mass activity, initial sperm motility, live sperm, sperm concentration, sperm number per ejaculate, cold shock resistance index, live intact acrosome, head abnormalities, mid piece abnormalities, tail abnormalities and sperm with proximal and distal cytoplasmic droplet were 1.08 ± 0.05 and 1.18 ± 0.04 ml, 3.71+ and 3.92+, 82.94 ± 0.73 and 84.60 ± 0.61 per cent, 85.57 ± 0.52 and 86.03 ± 0.48 per cent, 3356.73 ± 83.06 and 3176.94 ± 53.92 million per ml, 3595.17 ± 122.08 and 3669.00 ± 126.42 million, 6.72 ± 0.22 and 6.77 ± 0.20 per cent, 85.18 ± 0.39 and 84.05 ± 0.41 per cent, 1.65 ± 0.13 and 1.50 ± 0.12 per cent, 0.25 ± 0.02 and 0.30 ± 0.03 per cent, 2.73 ± 0.18 and 2.53 ± 0.13 per cent, 0.43 ± 0.03 and 0.48 ± 0.04 per cent and 0.86 ± 0.12 and 0.61 ± 0.04 per cent respectively. The different semen characteristics did not differ significantly between breeds; however, the differences between bucks within the breed were significant for ejaculate volume, live intact acrosome, mid piece abnormalities, tail abnormalities and sperm with distal cytoplasmic droplet.

Cold-Shock Resistance of Activated Sludge Microorganisms Strengthened by a Static Magnetic Field

Cold-Shock Resistance of Activated Sludge Microorganisms Strengthened by a Static Magnetic Field

Effects of sintering temperature and V2O5 additive on the properties of SiC-Al2O3 ceramic foams

In this study, a series of SiC-Al2O3 ceramic foams (SACFs) were fabricated from the powders of commercial silicon carbide and fused white corundum by polymeric foam replication method combined with reaction sintering process. Effects of sintering temperature (1250 °C-1350 °C) and addition amounts of V2O5 (0–3 wt%) on the sintering properties and post-sintering properties of as-prepared SACFs such as appearances, microstructures, phase compositions, apparent porosity, bulk density, cold compressive strength and thermal shock resistance have been investigated. During the sintering process, SiC was oxidized in air and formed SiO2, then part of as-formed SiO2 reacted with Al2O3 to produce Al6Si2O13 ceramic phase. The mechanical properties of as-prepared SACFs were found to be remarkably increased due to the increase of the sintering temperature and the introduction of V2O5. The phase transformation towards mullite was also found to be promoted, and the mullitization temperature was reduced because of the formation of Si-rich liquid phase due to the addition of V2O5. The improvements in sintering properties, cold compressive strength and thermal shock resistance of as-prepared SACFs were attributed to the formation of mullite and silica ceramic bonding phases in the ceramic matrix during the sintering process in air. The SACFs doped with 1 wt% V2O5 and sintered at 1450 °C for 2 h, achieved their maximum cold compressive strength of 2.45 MPa, and the apparent porosity was still 69.08%.

Cholesterol-loaded cyclodextrin improves ram sperm cryoresistance in skim milk-extender

Cholesterol-loaded cyclodextrin (CLC) is known to improve ram sperm cryosurvival. This study expands on previous research to: (1) determine the mechanism by which CLC improves ram sperm cryosurvival and (2) compare the efficiency of a novel, skim milk-based extender containing CLC to a traditional egg yolk-based extender. Hypothesis #1 was that CLC enhances membrane cholesterol content to increase the resistance of ram sperm to cold and osmotic stress, thereby improving cryosurvival. We first assessed the ability of fresh sperm treated with CLC to withstand cold shock. Second, fresh sperm were treated with CLC to evaluate their tolerance to osmotic stress. Third, to confirm that cholesterol is incorporated into the sperm using CLC, we quantified sperm cholesterol. To test Hypothesis #2 that CLC is most effective in a medium without competing cholesterol, we compared sperm cryosurvival and fertility in skim milk-based extender containing CLC versus in a traditional egg yolk-based freezing extender without CLC. Our data confirmed that CLC treatment improves ram sperm cold shock and osmotic stress resistance, and augments sperm cholesterol content. Semen in skim milk-based extender containing CLC prior to freezing, had more motile sperm with intact acrosomes after thawing compared to semen in egg yolk-based extender. In contrast, sperm plasma membrane integrity and in vivo fertility of the semen cryopreserved in the skim milk-based extender with CLC did not differ from semen that was cryopreserved in egg yolk-based extender. Further research is warranted to combine CLC with other cryoprotection strategies or to modify the insemination protocol.

The effect of oxidative stress on gene expression of Shiga toxin-producing Escherichia coli (STEC) O157:H7 and non-O157 serotypes

Understanding the survival mechanisms used by Shiga toxin-producing Escherichia coli (STEC), including O157:H7 and non-O157 serotypes, is important for minimizing contamination of fresh produce and occurrence of foodborne outbreaks. Recent outbreaks linked to leafy green vegetables and sprouted seeds have prompted researchers to focus on investigating decontamination strategies. Several studies showed that hydrogen peroxide (H2O2) treatment has been effective in reducing pathogens on fresh produce. As such, the effect of hydrogen peroxide on stress-associated and virulence gene expression in six STEC isolates was investigated in this study. Logarithmic phase cells of E. coli O157:H7 (EDL933) and non-O157 serotypes, including E. coli O26:H11 (EC20070549), O103:H2 (EC19970811), O104:H4 (NML#11-3088), O111:NM (EC20070546) and O145:NM (EC19970355) were exposed to 2.5mM H2O2 for 40min and gene expression was evaluated using quantitative real-time PCR. Different patterns of gene expression were observed in E. coli O157:H7 and non-O157 serotypes. Particularly, Shiga toxin gene stx2 was upregulated in O157:H7, but not in O104:H4. Moreover, stx1 was significantly upregulated in STEC O157:H7, but only slightly upregulated Stx1-positive non-O157 serotypes. However genes related to motility (fliC) and intimin gene (eae) were downregulated in most strains. Stress-associated sodA gene encoding manganese superoxide dismutase was significantly upregulated in all serotypes. The dps gene coding for non-specific DNA binding protein was upregulated in O145:NM, O111:NM, O103:H2 and O26:H11. However genes related to cold shock (cspC) and acid resistance (gadW) were significantly downregulated in all strains tested. The results of this study provide a basic understanding of the oxidative stress impact on survival and virulence of non-O157 serotype STEC strains.

Influence of selected factors on bovine spermatozoa cold shock resistance

The objectives of this study were to determine the effects of sire, extender, and addition of Low Density Lipoprotein (LDL) to extenders used on the percentage rate of spermatozoa survival after cold shock. Two groups of extenders were compared: without LDL addition (control variants) and LDL enriched (experimental variants). Three extenders were used: AndroMed®, Bioxcell®, and Triladyl®. Experimental variants included 4–8% LDL addition into the AndroMed® and Bioxcell® extenders, and 6–10% LDL addition into the Triladyl® extender. In total, 12 samples of fresh semen were collected from 4 bulls during a period of 8 weeks. Bovine spermatozoa cold shock resistance (1 ± 1 °C, 10 min) was evaluated by the percentage rate of live sperm using eosin-nigrosine staining immediately and after heat incubation (37 ± 1 °C, 120 min). The results showed the effect of sire as important and individual differences between selected sires in their sperm resistance against cold shock were confirmed. AndroMed® and Bioxcell® were found to be providing better protection of bull semen to cold shock compared to Triladyl® due to lower decline of live sperm proportion. Our results detected a positive effect of LDL addition on sperm resistance against cold shock, especially on lower decrease of live sperm percentage rate after 120 min of the heat test (P < 0.05). Further studies are needed to assess the optimal concentration of LDL in various kinds of extenders as well to state ideal time and temperature conditions for ensuring LDL reaction with sperm.

Preparation and properties of Al2O3–MgAl2O4 ceramic foams

In this work, a series of alumina (Al2O3)–magnesium aluminate (MgAl2O4) ceramic foams (AMCFs) were fabricated from powders of fused white corundum and magnesia (MgO) by a polymeric foam replication method combined with a reaction sintering process. The effects of MgO content and sintering temperature on the sintering properties and post-sintering properties of the AMCFs such as phase composition, appearance, microstructure, cold compressive strength and thermal shock resistance have been investigated. During the sintering process, MgO reacted with Al2O3 to form MgAl2O4 ceramic phase, which contributed to the improvement in sintering properties, cold compressive strength and thermal shock resistance of the AMCFs. The AMCFs doped with 8wt% MgO and sintered at 1450°C for 2h displayed high cold compressive strength of 0.89MPa, good sintering properties and thermal shock resistance. Although their apparent porosities were about 87%, the cold compressive strength of as-prepared foam was about 1.3 times higher than that of commercial Al2O3 foam.

Effect of cholesterol-loaded cyclodextrins on bull and goat sperm processed with fast or slow cryopreservation protocols

Cholesterol-loaded cyclodextrins (CLC) added to the sperm before cryopreservation enhance sperm quality after freeze-thawing in several cold shock-sensitive species, including cattle and goats. However, all studies conducted to date have used conventional protocols, in which sperm are cooled slowly to 5°C before freezing. As cholesterol plays a significant role in sperm cold shock resistance, it is possible that CLC-treated sperm can withstand cooling damage when the sperm are not cooled slowly to 5°C before freezing. In this study, we determined whether CLC-treated goat (1 mg CLC/120×106 sperm) and bull (2 mg CLC/120×106 sperm) sperm quality, after thawing, was different for sperm frozen using conventional protocols (including a slow cooling phase to 5ºC) and protocols in which the sperm were frozen from room temperature, without cooling the sperm slowly to 5°C before freezing. CLC-treated sperm exhibited higher percentages of plasma membrane-intact sperm than control sperm when cryopreserved using conventional protocols. In addition, CLC treatment enhanced both sperm motility and plasma membrane integrity when sperm were frozen directly from room temperature. However, this treatment did not fully prevent the damage of the sperm after cooling rapidly and subsequent freezing, as the sperm quality was lower than that presented by the samples frozen using the conventional protocol. The results are promising, but studies to optimize the protocols for freezing sperm directly from room temperature need to be conducted, as well as studies to determine how cryopreserving sperm in this manner affects other sperm functions.

Locomotor activity of Drosophila melanogaster in high temperature environments: plastic and evolutionary responses

Regular exposure to a given stressor poses selective pressure towards increased resis- tance. In high temperature environments this can be mediated through physiological and biochemi- cal adjustments that lead to increased resistance to heat coma. Such adjustments may influence com- plex traits such as locomotor activity through cascading effects. Alternatively, changes in locomotor activity may change the exposure to the stressor and, thereby, the importance of the physiological and biochemical adjustments. In this experiment we analysed how selection for heat shock resistance may affect locomotor activity at high temperatures in Drosophila melanogaster. We compared 2 lines selected for heat shock (HS) and cold shock (CS) resistance at 4 constant high temperatures (28 to 38°C). We also tested the importance of heat shock protein (Hsp) expression by comparing locomotor activity at the same temperatures of a heat-sensitive mutant line (Hsf 0 ), where the heat shock factor (Hsf) is non-functional at high temperatures, with that of a rescued mutant line (Hsf + ) with a functional Hsf re-inserted. At moderately stressful temperatures (28 and 34°C), flies from the Hsf 0 line were more active than flies from the Hsf + line, whereas this was reversed at higher temperatures. In the selection lines, the CS flies were more active at 28°C but this was reversed at 34 and 36°C, whereas no difference was observed at the most stressful temperature (38°C). This suggests that the lines selected for increased cold tolerance were more stressed at moderately high temperatures and, there- fore, more active in the attempt to escape the stress, whereas at higher temperatures, their locomotor activity was more compromised than in flies from the lines selected for increased heat resistance.

ATP analysis of boar sperm, with or without cold shock resistance, by various preservation methods

ATP analysis of boar sperm, with or without cold shock resistance, by various preservation methods

REPRODUCTIVE DIAPAUSE AND LIFE-HISTORY CLINES IN NORTH AMERICAN POPULATIONS OF DROSOPHILA MELANOGASTER

Latitudinal clines are widespread in Drosophila melanogaster, and many have been interpreted as adaptive responses to climatic variation. However, the selective mechanisms generating many such patterns remain unresolved, and there is relatively little information regarding how basic life-history components such as fecundity, life span and mortality rates vary across environmental gradients. Here, it is shown that four life-history traits vary predictably with geographic origin of populations sampled along the latitudinal gradient in the eastern United States. Although such patterns are indicative of selection, they cannot distinguish between the direct action of selection on the traits in question or indirect selection by means of underlying genetic correlations. When independent suites of traits covary with geography, it is therefore critical to separate the widespread effects of population source from variation specifically for the traits under investigation. One trait that is associated with variation in life histories and also varies with latitude is the propensity to express reproductive diapause; diapause expression has been hypothesized as a mechanism by which D. melanogaster adults overwinter, and as such may be subject to strong selection in temperate habitats. In this study, recently derived isofemale lines were used to assess the relative contributions of population source and diapause genotype in generating the observed variance for life histories. It is shown that although life span, fecundity and mortality rates varied predictably with geography, diapause genotype explained the majority of the variance for these traits in the sampled populations. Both heat and cold shock resistance were also observed to vary predictably with latitude for the sampled populations. Cold shock tolerance varied between diapause genotypes and the magnitude of this difference varied with geography, whereas heat shock tolerance was affected solely by geographic origin of the populations. These data suggest that a subset of life-history parameters is significantly influenced by the genetic variance for diapause expression in natural populations, and that the observed variance for longevity and fecundity profiles may reflect indirect action of selection on diapause and other correlated traits.

Comparison of Motility, Acrosome, Viability and ATP of Boar Sperm with or without Cold Shock Resistance in Liquid Semen at 17째C and 4째C, and Frozen-thawed Semen

This study was designed to analyze boar sperm to compare motility, acrosome morphology, viability and ATP by various preservation methods between Duroc boar A with cold shock resistance sperm and Duroc boar B with cold shock sensitivity sperm. Semen volume, sperm concentration, motility and normal acrosome between Duroc boar A and B did not show any differences within 2 h after collection. There were no differences in sperm motility and normal acrosome between boar A and B at 1 day of preservation at 17°C and 4°C, respectively. However, sperm motility and normal acrosome from 2 day of preservation at 17°C and 4°C, respectively, were higher for boar A than boar B. The frozen-thawed sperm motility and normal acrosome were higher for boar A than boar B. The sperm viability and ATP concentration according to storage period of liquid semen at 17°C and 4°C were higher for boar A than boar B. Also, the sperm viability and ATP concentration of frozen-thawed semen were higher for boar A than boar B. In conclusion, we found out that the original quality of boar semen with cold shock resistance sperm played an important role.

Differential cold-shock resistance among acclimated European mussel populations

To study differential cold-shock resistance of marine mussel populations (Mytilus spp.) from different climatic regions in Europe, we sampled 12 populations, ranging from 43 to 58°N. Minimum critical temperatures for aerobic metabolism (CTmin) were determined before and after 3 months of common acclimatization in an outdoor mesocosm. Additionally, chill coma in response to cold shock was used to test for differences in physiological plasticity between the translocated populations. The CTmin followed a steep cline, being positively related to the ambient temperatures before translocation (p < 0.0001), and became similar between populations after 3 months in the outdoor mesocosms (p > 0.05). Differential chill coma responses separated the populations into two groups that were also geographically separated by the English Channel. The southern populations showed a much stronger and faster sensitivity to chill than the northern populations, indicating differential physiological adaptation between the two groups. The results are discussed in relation to the genetic background and climatic isolation of the populations.

The influence of developmental stage on cold shock resistance and ability to cold-harden in Drosophila melanogaster

Thermal sensitivity and ability to rapidly cold- and heat-harden may change during ontogeny. This study reports how inherent cold tolerance and ability to rapidly cold-harden change across eight developmental stages in both genders of Drosophila melanogaster using a similar experimental approach for all stages. Inherent cold tolerance was estimated as LT50 by assaying cold shock survival over a wide range of temperatures (-16 to 5 degrees C). Rapid cold-hardening (RCH) was applied by cooling from 25 to 0 degrees C at -0.25 degrees C min(-1) followed by 1 h at 0 degrees C. Individuals were cold shocked either directly or after RCH to estimate the effect of RCH. We found large variation in cold tolerance among developmental stages and minor differences between genders. Eggs were most tolerant followed by adults, pupae and larvae. In the light of this and other studies it is suggested that there is a general pattern of stage specific thermal stress resistance in Drosophila. The capacity to rapidly cold-harden was found in both sexes of larval, pupal and adult stages, though some developmental stages showed negative or neutral effects of RCH which was probably due to the cost associated with the hardening treatment in these cold susceptible stages. The early presence of RCH indicates that the mechanisms behind hardening are not stage specific and that RCH may be an ecologically important trait in early stages of ontogeny.

The influence of developmental stage on cold shock resistance and ability to cold-harden in Drosophila melanogaster

Thermal sensitivity and ability to rapidly cold- and heat-harden may change during ontogeny. This study reports how inherent cold tolerance and ability to rapidly cold-harden change across eight developmental stages in both genders of Drosophila melanogaster using a similar experimental approach for all stages. Inherent cold tolerance was estimated as LT 50 by assaying cold shock survival over a wide range of temperatures ( - 16 to 5 ∘ C ) . Rapid cold-hardening (RCH) was applied by cooling from 25 to 0 ∘ C at - 0.25 ∘ C min - 1 followed by 1 h at 0 ∘ C . Individuals were cold shocked either directly or after RCH to estimate the effect of RCH. We found large variation in cold tolerance among developmental stages and minor differences between genders. Eggs were most tolerant followed by adults, pupae and larvae. In the light of this and other studies it is suggested that there is a general pattern of stage specific thermal stress resistance in Drosophila. The capacity to rapidly cold-harden was found in both sexes of larval, pupal and adult stages, though some developmental stages showed negative or neutral effects of RCH which was probably due to the cost associated with the hardening treatment in these cold susceptible stages. The early presence of RCH indicates that the mechanisms behind hardening are not stage specific and that RCH may be an ecologically important trait in early stages of ontogeny.