Critical thermal limits,temperature tolerance and water balance of a sub-Antarctic caterpillar,Pringleophaga marioni (Lepidoptera: Tineidae)

Thermal tolerance, supercooling point, water balance and osmoregulatory ability of Pringleophaga marioni Viette (Lepidoptera: Tineidae) are investigated in this study. Field-fresh larvae had a mean CT(Min) (cold stupor) of -0.6 degrees C and a mean CT(Max) (heat coma) of 38.7 degrees C. The mean supercooling point of field-fresh individuals was -5.0 degrees C. Caterpillars showed 100% survival of freezing to -6.5 degrees C, but at -12 degrees C mortality rose to 100%. Survival of a 30h exposure to -6.0 degrees C was 80%, but declined to 30% in the 6-12h interval at -7.5 degrees C. No caterpillars survived for longer than 12h at -9.0 degrees C. Survival of high temperatures (35 degrees C and above) was poor. Tolerance of water loss (46% of fresh mass) and rates of water loss (1% fresh massh(-1)) were similar to those found in other mesic insects. P. marioni larvae were incapable of metabolizing lipids to replenish lost water and showed no haemolymph osmoregulatory ability. It is suggested that the preponderance of freeze tolerance in high-latitude southern hemisphere species may be associated with their occurrence in moist habitats, and that the "freeze tolerance" category be re-examined in the light of the range of strategies adopted by such arthropods.     

Cold hardiness,supercooling ability and causes of low-temperature mortality in the soft tick,Argas reflexus,and the hard tick,Ixodes ricinus (Acari: Ixodoidea) from Central Europe

Seasonal supercooling points (SCPs=temperature of crystallization) and cold hardiness were investigated in the indigenous hard tick, I. ricinus, and in A. reflexus, a soft tick introduced to Central Europe from the South. Both species proved to be freeze-susceptible as well as highly susceptible to inoculative freezing. None of the postembryonic developmental stages of either species showed any distinct seasonal pattern of SCP. Unexpectedly, the introduced A. reflexus exhibited a distinctly higher degree of cold hardiness in terms of lower lethal temperature (LT(50): 24h exposure) as well as lethal time (T(50): time of survival at -10.1 degrees C) than I. ricinus. Engorged I. ricinus larvae as well as engorged summer acclimatized A. reflexus larvae showed some mortality at temperatures well above the SCP. This mortality was generally expressed as a failure of the following stage to eclose properly. A 10-day cold acclimation at +3 degrees C eliminated that kind of mortality in summer acclimatized A. reflexus larvae, but not in I. ricinus larvae. It was frequently observed that freezing of ticks resulted-possibly via leakage from the midgut-in a subsequent reddish brown discoloration of the ticks after thawing. Taking into account that discoloration was an indication of previous freezing, it was concluded, that after long-term exposure (for >/=30 days) at -10.1 degrees C, a temperature well above the SCP, some tick mortality could be observed that was not caused by previous freezing. Weighing experiments clearly demonstrated, that the level of dehydration was not critical for survival of A. reflexus during long-term cold exposure, even at low RH. This indicates, that cold-related factors other than freezing and dehydration were detrimental to this species.     

Effects of summer frost exposures on the cold tolerance strategy of a sub-Antarctic beetle

The sub-Antarctic beetle Hydromedion sparsutum (Coleoptera, Perimylopidae) is common locally on the island of South Georgia where sub-zero temperatures can be experienced in any month of the year. Larvae were known to be weakly freeze tolerant in summer with a mean supercooling point (SCP) around -4 degrees C and a lower lethal temperature of -10 degrees C (15min exposure). This study investigated the effects of successive freezing exposures on the SCP and subsequent survival of summer acclimatised larvae. The mean SCP of field fresh larvae was -4.2+/-0.2 degrees C with a range from -1.0 to -6.1 degrees C. When larvae were cooled to -6.5 degrees C on 10 occasions at intervals of 30min and one and four days, survival was 44, 70 and 68%, respectively. The 'end of experiment' SCP of larvae surviving 10 exposures at -6.5 degrees C showed distinct changes and patterns from the original field population depending on the interval between exposure. In the 30min interval group, most larvae froze between -6 and -8 degrees C, a depression of up to 6 degrees C from the original sample; all larvae were dead when cooling was continued below the SCP to -12 degrees C. In the one and four day interval groups, most larvae froze above -6 degrees C, showing no change as a result of the 10 exposures at -6.5 degrees C. As with the 30min interval group, some larvae froze below -6 degrees C, but with a wider range, and again, all were dead when cooled to -12 degrees C. However, in the one and four day interval groups, some larvae remained unfrozen when cooled to -12 degrees C, a depression of their individual SCP of at least 6 degrees C, and were alive 24h after cooling. In a further experiment, larvae were cooled to their individual SCP temperature at daily intervals on 10 occasions to ensure that every larva froze every day. Most larvae which showed a depression of their SCP of 2-4 degrees C from their day one value became moribund or died after six or seven freezing events. Survival was highest in larvae with SCPs of -2 to -3 degrees C on day one and which froze at this level on all 10 occasions. The results indicate that in larvae in which the SCP is lowered following sub-zero exposure, the depression of the SCP is greatest in individuals that do not actually freeze. Further, the data suggest that after successive frost exposures in early winter the larval population may become segregated into two sub-populations with different overwintering strategies. One group consists of larvae that freeze consistently in the temperature range from -1 to -3 degrees C and can survive multiple freeze-thaw cycles. A second group with lower initial SCPs (around -6 degrees C), or which fall to this level or lower (down to -12 degrees C) after freezing on one or more occasions, are less likely to freeze through extended supercooling, but more likely to die if freezing occurs.     

The effects of acclimation on thermal tolerance, desiccation resistance and metabolic rate in Chirodica chalcoptera (Coleoptera: Chrysomelidae)

Despite much focus on species responses to environmental variation through space and time, many higher taxa and geographic areas remain poorly studied. We report the effects of temperature acclimation on thermal tolerance, desiccation rate and metabolic rate for adult Chirodica chalcoptera (Coleoptera: Chrysomelidae) collected from Protea nerifolia inflorescences in the Fynbos Biome in South Africa. After 7 days of acclimation at 12, 19 and 25 degrees C, critical thermal maxima (mean+/-s.e.: 41.8+/-0.2 degrees C in field-fresh beetles) showed less response (<1 degrees C change) to temperature acclimation than did the onset of the critical thermal minima (0.1+/-0.2, 1.0+/-0.2 and 2.3+/-0.2 degrees C, respectively). Freezing was lethal in C. chalcoptera (field-fresh SCP -14.6 degrees C) and these beetles also showed pre-freeze mortality. Survival of 2 h at -10.1 degrees C increased from 20% to 76% after a 2 h pre-exposure to -2 degrees C, indicating rapid cold hardening. Metabolic rate, measured at 25 degrees C and adjusted by ANCOVA for mass variation, did not differ between males and females (2.772+/-0.471 and 2.517+/-0.560 ml CO2 h(-1), respectively), but was higher in 25 degrees C-acclimated beetles relative to the field-fresh and 12 degrees C-acclimated beetles. Body water content and desiccation rate did not differ between males and females and did not respond significantly to acclimation. We place these data in the context of measured inflorescence and ambient temperatures, and predict that climate change for the region could have effects on this species, in turn possibly affecting local ecosystem functioning.     

Cold hardiness of the fly pupal parasitoid Nasonia vitripennis is enhanced by its host Sarcophaga crassipalpis

Supercooling points (SCPs) and low temperature survival were determined for diapausing and nondiapausing larvae of the ectoparasitoid Nasonia vitripennis. Neither nondiapausing nor diapausing larvae could survive tissue freezing. The SCP profiles were nearly identical for nondiapause-destined (-27 degrees C) and diapausing larvae (-25 degrees C), but these values were not indicative of the lower limits of tolerance in either type of larvae: larvae were killed by chilling at temperatures well above the SCP. Diapausing larvae could withstand low temperature exposures 3-8 times longer than their nondiapausing counterparts. Low temperature survival was enhanced in diapausing and nondiapausing larvae by their encasement within the puparium of the host flesh fly, SARCOPHAGA CRASSIPALPIS: the LT(50)s determined for nondiapausing and diapausing larvae enclosed by fly puparia were 2-3 times higher than values calculated for larvae removed from the puparia. Additional low temperature protection was gained through acquisition of host cryoprotectants during larval feeding: nondiapausing parasitoid larvae that fed on diapausing flesh fly pupae with high levels of glycerol were able to survive exposure to a subzero temperature 4-9 times longer than wasps reared on nondiapausing fly pupae that contained lower quantities of glycerol. Alanine may also contribute to the cold hardiness of N. vitripennis, as evidenced by the fact that larvae feeding on diapausing fly pupae both contained higher concentrations of alanine and exhibited greater cold hardiness. The results thus demonstrate that several critical features of cold hardiness in the wasp are derived from biochemical and physical attributes of the host.     

Cold hardiness of Habrobracon hebetor (Say) (Hymenoptera: Braconidae), a parasitoid of pyralid moths

The ectoparasitoid Habrobracon hebetor (Say) attacks stored-product infesting pyralid moths that are able to overwinter under extremely cold conditions. The extent to which H. hebetor can withstand these conditions is not known, but has important implications for the ability of H. hebetor to provide long-term suppression of these pests in temperate climates. We investigated basic cold hardiness aspects of a mutant eye-color strain of H. hebetor. Feeding larvae and adults of H. hebetor had supercooling points (SCPs) at temperatures higher than those of eggs and pupae. Mean SCPs of females and males were equivalent, as were those of naked and silk-encased pupae. Feeding on honey prior to being subjected to low temperatures significantly increased the SCP of adult females by approximately 8 degrees C. Mortality of pupae and adults increased significantly whenever the temperature dropped below the mean SCP, indicating that H. hebetor does not tolerate freezing. For pupae and adults exposed to -12 and -5 degrees C, the hourly mortality rate increased with time of exposure. Pupae and adults exposed to -12 degrees C for different time intervals showed high mortality after only 1d of exposure. At -5 degrees C, none survived 12d of exposure. A better understanding of how well this parasitoid tolerates low temperatures will be useful in evaluating its potential as a biological control agent of stored-product moths in temperate regions.     

Critical thermal limits, temperature tolerance and water balance of a sub-Antarctic kelp fly, Paractora dreuxi (Diptera: Helcomyzidae)

Paractora dreuxi displays distinct ontogenetic differences in thermal tolerance and water balance. Larvae are moderately freeze tolerant. Mean larval onset of chill coma was -5.1 degrees C, and onset of heat stupor was 35.5 degrees C. Larval supercooling point (SCP) was -3.3 degrees C with 100% recovery, although mortality was high below -4 degrees C. Starvation caused SCP depression in the larvae. Adults were significantly less tolerant, with critical thermal limits of -2.7 and 30.2 degrees C, no survival below the SCP (-9.6 degrees C), and no change in SCP with starvation. Moderate freeze tolerance in the larvae supports the contention that this strategy is common in insects from southern, oceanic islands. Fly larvae survived desiccation in dry air for 30 h, and are thus less desiccation tolerant than most other sub-Antarctic insect larvae. Water loss rates of the adults were significantly lower than those of the larvae. Lipid metabolism did not contribute significantly to water replacement in larvae, which replaced lost body water by drinking fresh water, but not sea water. Kelp fly larvae had excellent haemolymph osmoregulatory abilities. Current climate change has led to increased temperatures and decreased rainfall on Marion Island. These changes are likely to have significant effects on P. dreuxi, and pronounced physiological regulation in larvae suggests that they will be most susceptible to such change.     

Freeze mortality characteristics of the mold mite Tyrophagus putrescentiae, a significant pest of stored products

The mold mite Tyrophagus putrescentiae (Shrank) is a common pest of stored food products. Until recently, commodity and facility treatments have relied on acaricides and fumigants to control this mite. However, T. putrescentiae will cause infestations in areas where acaricide or fumigant use may be restricted, prohibited, or highly impractical. Because temperature is an essential factor that limits the survival of arthropod species, extreme temperatures can be exploited as an effective method of control. Making low-temperature treatments reliable requires better temperature-time mortality estimates for different stages of this mite. This was accomplished by exposing a representative culture (eggs, nymphs, and adults) of noncold-acclimated T. putrescentiae to subfreezing temperatures to determine their supercooling points (SCPs), lower lethal temperatures (LLTs) and lethal times (LTimes) at set temperatures. The results indicate that the adult and nymphal stages of T. putrescentiae are freeze intolerant; based on 95% CIs, the adult LLT90 of -22.5 degrees C is not significantly different from the SCP of -24.2 degrees C and the nymphal LLT90 of -28.7 degrees C is not significantly different from the SCP of -26.5 degrees C. The egg stage seems to be freeze tolerant, with an LLT90 of -48.1 degrees C, significantly colder by approximately 13.5 degrees C than its SCP of -35.6 degrees C. The LTime demonstrates that 90% of all mite stages of T. putrescentiae can be controlled within commodity or packaged product by freezing to -18 degrees C for 5 h. By achieving the recommended time and temperature exposures, freezing conditions can be an effective way of controlling mites and reducing chronic infestations.     

Cold-Hardiness and Supercooling Capacity in Diapausing and Nondiapausing Stages of the Cabbage Root Fly Delia radicum

Supercooling point (SCP) values and cold-hardiness were measured in individual ontogenetic stages of Delia radicum (Diptera:Anthomyiidae) in various physiological states (winter diapause, summer quiescence, and normal development). Winter diapause-destined mature third-instar larvae had a lower SCP (-9.9 degrees C) than their nondiapause counterparts (-5.2 degrees C), and more of them survived exposure to -10 degrees C for 5 h to pupariation and adult emergence. Values of SCPs were equal in both diapause and nondiapause states of prepupal and pupal stages. The lowest SCP (ca. -20 degrees C) was found in the stage of phanerocephalic pupa (PCP) regardless of the physiological state. The cold-hardiness of PCP corresponded with a low SCP value only in diapausing pupae stored for 80 days at 3 degrees C and in pupae which had terminated their diapause and whose further development was inhibited by storage at low temperatures (3 degrees C). Such pupae survived exposure to temperatures close to their SCP (14 days at -17 degrees C). However, this high cold-hardiness was only acquired after some time and/or exposure to 3 degrees C, as the PCP at the beginning of diapause showed significantly impaired cold-hardiness despite the fact that their SCP was low. The cold-hardiness of nondiapausing PCP did not correspond at all to that of low SCP, as no pupa survived the exposure to -17 degrees C for 1 day; survival rates at temperatures of -13.5 and -10 degrees C were also remarkably lower than those in diapausing pupae. Cold-hardiness in D. radicum was closely connected with the diapause syndrome but the changes in SCP value corresponded rather with the ontogeny of this insect. Copyright 1993, 1999 Academic Press.     

Relationship between supercooling point and mortality at low temperatures in Indianmeal moth (Lepidoptera: Pyralidae)

Indianmeal moth, Plodia interpunctella (Hübner), is classified as a freeze-intolerant organism and one of the most cold-tolerant stored-product pests. The objective of this study was to determine the relationship between mortality at low temperatures after minimum exposure and the supercooling point (SCP) for laboratory-reared P. interpunctella at different stages of development. This relationship also was analyzed for field-collected, cold-acclimated fifth instars. Mean SCP of laboratory-reared larvae (i.e., feeding stage) was consistently above approximately -16 degrees C. Mean SCP of laboratory-reared pupae and adults (i.e., nonfeeding stages) and field-collected, cold-acclimated fifth instars was consistently below approximately -21 degrees CP seemed to be the boundary between survival and death for larvae. However, it seemed that a 1-min exposure was not sufficient to cause larval mortality at the SCP. Alternatively, for both pupae and adults, the SCP seemed not to play an important role in their survival at low temperatures, with significant mortality observed at temperatures higher than the mean SCP. Adults were the most susceptible to low temperatures with no survival occurring at -20 degrees C, > 3 degrees C above its mean SCP. Results of this investigation demonstrate that P. interpunctella has a different response to low temperatures depending on stage of development and cold acclimation. Classifying P. interpunctella only as a freeze-intolerant organism disregards the occurrence of prefreeze mortality in this species. Therefore, a reclassification of this species (e.g., chill tolerant or chill susceptible) based on the extent of prefreeze mortality and the temperature and time of exposure at which it occurs is suggested.     

Desiccation stress at sub-zero temperatures in polar terrestrial arthropods

Cold tolerant polar terrestrial arthropods have evolved a range of survival strategies which enable them to survive the most extreme environmental conditions (cold and drought) they are likely to encounter. Some species are classified as being freeze tolerant but the majority of those found in the Antarctic survive sub-zero temperatures by avoiding freezing by supercooling. For many arthropods, not just polar species, survival of desiccating conditions is equally important to survival of low temperatures. At sub-zero temperatures freeze avoiding arthropods are susceptible to desiccation and may lose water due to a vapour diffusion gradient between their supercooled body fluids and ice in their surroundings. This process ceases once the body fluids are frozen and so is not a problem for freeze tolerant species. This paper compares five polar arthropods, which have evolved different low temperature survival strategies, and the effects of exposure to sub-zero temperatures on their supercooling points (SCP) and water contents. The Antarctic oribatid mite (Alaskozetes antarcticus) reduced its supercooling point temperature from -6 to -30 degrees C, when exposed to decreasing sub-zero temperatures (cooled from 5 to -10 degrees C over 42 days) with little loss of body water during that period. However, Cryptopygus antarcticus, a springtail which occupies similar habitats in the Antarctic, showed a decrease in both water content and supercooling ability when exposed to the same experimental protocol. Both these Antarctic arthropods have evolved a freeze avoiding survival strategy. The Arctic springtail (Onychiurus arcticus), which is also freeze avoiding, dehydrated (from 2.4 to 0.7 g water g(-1) dry weight) at sub-zero temperatures and its SCP was lowered from c. -3 to below -15 degrees C in direct response to temperature (5 to -5.5 degrees C). In contrast, the freeze tolerant larvae of an Arctic fly (Heleomyza borealis) froze at c. -7 degrees C with little change in water content or SCP during further cold exposure and survived frozen to -60 degrees C. The partially freeze tolerant sub-Antarctic beetle Hydromedion sparsutum froze at c. -2 degrees C and is known to survive frozen to -8 degrees C. During the sub-zero temperature treatment, its water content reduced until it froze and then remained constant. The survival strategies of such freeze tolerant and freeze avoiding arthropods are discussed in relation to desiccation at sub-zero temperatures and the evolution of strategies of cold tolerance.     

Diurnal variation in supercooling points of three species of Collembola from Cape Hallett, Antarctica

Daily changes in microclimate temperature and supercooling point (SCP) of Collembola were measured during summer at Cape Hallett, North Victoria Land, Antarctica. Isotoma klovstadi and Cryptopygus cisantarcticus (Isotomidae) showed bimodal SCP distributions, predominantly in the high group during the day and in the low group during the night. There were no concurrent diurnal changes in water content or haemolymph osmolality. By contrast, Friesea grisea (Neanuridae) had a unimodal distribution of SCPs that was invariant between daytime and nighttime. Isotoma klovstadi collected foraging on moss had uniformly high SCPs, which shifted towards the low group when the animals were starved for 2-8 h. When I. klovstadi was acclimated for five days with lichen or algae, SCPs were higher than if they were supplied with moss, while those that were starved (with free water or 100% relative humidity) displayed a trimodal SCP distribution. A variety of pre-treatments, including cold, heat, desiccation and slow cooling were ineffective at inducing SCP shifts in C. cisantarcticus or I. klovstadi. It is postulated that behavioural avoidance of low temperatures by vertical migration may be key in I. klovstadi's short-term survival of nighttime temperatures. These data suggest that the full range of thermal responses of Antarctic Collembola is yet to be elucidated.     

Cold tolerance in diapausing and non-diapausing stages of the flesh fly, Sarcophaga crassipalpis

ABSTRACT. Supercooling points (SCP) and low temperature tolerance were determined for larval, pupal and adult stages of Sarcophaga crassipalpis Macquart (Diptera: Sarcophagidae). No stage tolerates tissue-freezing. Ontogenetic changes in SCP profiles are similar for comparable developmental stages of diapause and non-diapause groups. Feeding larvae have SCPs near -7°C which decrease to -11°C in the postfeeding wandering phase of the final larval instar. The lowest SCPs are recorded for pupae at -23°C. The capacity to survive at -17°C varies with age of the diapausing pupae: 10-day-old pupae are less cold tolerant than pupae that have been in diapause for 45–80 days. Although the SCP of non-diapausing pupae is as low as in diapausing pupae, non-diapausing pupae are extremely sensitive to low temperature exposure and do not survive to adult eclosion when exposed to -17°C for as little as 20 min. The use of hexane to break pupal diapause has no effect on SCPs or low temperature tolerance.     

Cold hardiness of Apteropanorpa tasmanica Carpenter (Mecoptera: Apteropanorpidae)

There are very few investigations of cold hardiness in native Australian insects, and no such studies on insects from Tasmania. The Apteropanorpidae is a family of wingless Mecoptera endemic to Tasmania, comprising four described species that can be active in winter. In this study, we used infrared video thermography to investigate the physiological and behavioural responses of Apteropanorpa tasmanica to fast (0.3 degrees Cmin(-1)) and slow (0.03 degrees Cmin(-1)) rates of temperature reduction down to -10 degrees C. No adults survived cooling to -10 degrees C at either cooling rate. Mean supercooling points (SCPs) from fast cooling were -7.0 and -4.6 degrees C in 2002 and 2003, respectively. Ice nucleation always began in the abdomen, however, the position of nucleation within the abdomen varied between individuals. There was no relationship between SCP and body length, and no significant difference in SCPs between males and females. Stress-induced fast walking began when insects reached approximately -1.5 degrees C. Cooling rate did not affect the SCP or the temperature at which the behavioural stress response began. Adults survived for only short periods of time in the supercooled state; however they survived in the laboratory for up to 60 days at 4 degrees C, indicating their longevity at more favourable temperatures. Members of the Apteropanorpidae are adapted to the relatively warm, maritime climate currently influencing Tasmania.     

Phenotypic plasticity of thermal tolerances in five oribatid mite species from sub-Antarctic Marion Island

The extent to which phenotypic plasticity might mediate short-term responses to environmental change is controversial. Nonetheless, theoretical work has made the prediction that plasticity should be common, especially in predictably variable environments by comparison with those that are either stable or unpredictable. Here we examine these predictions by comparing the phenotypic plasticity of thermal tolerances (supercooling point (SCP), lower lethal temperature (LLT), upper lethal temperature (ULT)), following acclimation at either 0, 5, 10 or 15 degrees C, for seven days, of five, closely-related ameronothroid mite species. These species occupy marine and terrestrial habitats, which differ in their predictability, on sub-Antarctic Marion Island. All of the species showed some evidence of pre-freeze mortality (SCPs -9 to -23 degrees C; LLTs -3 to -15 degrees C), though methodological effects might have contributed to the difference between the SCPs and LLTs, and the species are therefore considered moderately chill tolerant. ULTs varied between 36 degrees C and 41 degrees C. Acclimation effects on SCP and LLT were typically stronger in the marine than in the terrestrial species, in keeping with the prediction of strong acclimation responses in species from predictably variable environments, but weaker responses in species from unpredictable environments. The converse was found for ULT. These findings demonstrate that acclimation responses vary among traits in the same species. Moreover, they suggest that there is merit in assessing the predictability of changes in high and low environmental temperatures separately.     

The relationship between gut contents and supercooling capacity in hatchling painted turtles (Chrysemys picta)

Painted turtles (Chrysemys picta) typically spend their first winter of life in a shallow, subterranean hibernaculum (the natal nest) where they seemingly withstand exposure to ice and cold by resisting freezing and becoming supercooled. However, turtles ingest soil and fragments of eggshell as they are hatching from their eggs, and the ingestate usually contains efficient nucleating agents that cause water to freeze at high subzero temperatures. Consequently, neonatal painted turtles have only a modest ability to undergo supercooling in the period immediately after hatching. We studied the limit for supercooling (SCP) in hatchlings that were acclimating to different thermal regimes and then related SCPs of the turtles to the amount of particulate matter in their gastrointestinal (GI) tract. Turtles that were transferred directly from 26 degrees C (the incubation temperature) to 2 degrees C did not purge soil from their gut, and SCPs for these animals remained near -4 degrees C for the 60 days of the study. Animals that were held at 26 degrees C for the duration of the experiment usually cleared soil from their GI tract within 24 days, but SCPs for these turtles were only slightly lower after 60 days than they were at the outset of the experiment. Hatchlings that were acclimating slowly to 2 degrees C cleared soil from their gut within 24 days and realized a modest reduction in their SCP. However, the limit of supercooling in the slowly acclimating animals continued to decline even after all particulate material had been removed from their GI tract, thereby indicating that factors intrinsic to the nucleating agents themselves also may have been involved in the acclimation of hatchlings to low temperature. The lowest SCPs for turtles that were acclimating slowly to 2 degrees C were similar to SCPs recorded in an earlier study of animals taken from natural nests in late autumn, so the current findings affirm the importance of seasonally declining temperatures in preparing animals in the field to withstand conditions that they will encounter during winter.     

Biological control of an insect pest by gut-colonizing Enterobacter cloacae transformed with ice nucleation gene

The ice nucleation (IN) gene inaA of epiphytic Erwinia (Pantoea) ananas IN10 was transformed into Enterobacter cloacae WBMH-3-CMr originated from the faeces of silkworms. The transformant designated as Ent. cloacae WBMH-3-CMr(pICE6S13) exhibited IN activity, unlike the parent strain. The transgenic strain was ingested by mulberry pyralid larvae, fed on detached mulberry leaves, and the supercooling capacity and cold hardiness of these larvae were examined. The mean supercooling point (SCP) of the larvae ingesting the transgenic strain was - 3.3 degrees C, 8 degrees C higher than that of larvae treated with distilled water (control) and 1.5 C higher than an ice nucleation active (INA) strain of Erw. ananas. The SCPs of the larvae were stably maintained over the 9 d after ingestion. The maintenance of these high SCPs was due to transgenic Ent. cloacae having a more stable and efficient gut colonization than Erw. ananas, which is identified by the distribution of a narrower range of SCPs (-2 to -5 degrees C) in larvae treated with the transgenic stain. Furthermore, most of the larvae ingesting the transgenic strain froze and died when they were exposed to cold conditions of -5 degrees C for 18 h, 3 or 7 d after ingestion. In contrast, most of the larvae ingesting no bacterium did not die under similar conditions. On the other hand, the growth ability of Ent. cloacae WBMH-3-CMr on mulberry leaves tended to be lower than that of epiphytic Erw. ananas, as assayed by pot tests. These findings would expand the possibility of biological control using INA bacteria since Ent. cloacae would harbour a broader host (insect) range for gut colonization and a smaller affinity to plants to benefit from prevention of plant frost injury.     

Photoperiodic and thermal regulation of development and cold hardiness in larvae of the clover leaf weevil, Hypera punctata

Effects of photoperiod and temperature on the development and cold hardiness were investigated in larvae of Hypera punctata. At a relatively low temperature (15 degrees C), the larvae fed less and developed more slowly under a 12L:12D (SD) photoperiod than under a 16L:8D photoperiod (LD). SD larvae had lower gut weight against the whole body weight and lower supercooling point (SCP) than the LD counterparts for the same instar and same body weight. This was because the larval SCP is markedly affected by the quantity of the gut content. Laboratory experiments indicated that the low temperature mortality of this larvae occurred mainly due to freezing irrespective of the photoperiod and temperature, suggesting that the lower lethal temperature (LLT) depends on the supercooling ability of larvae. The SD larvae tended to have a lower SCP and hence a lower LLT than the LD counterparts at 15 or 10 degrees C, unlike at 20 degrees C. Thus, the slower larval development under SD conditions at relatively low temperatures may prevent larvae from reaching the later instar, which have a higher SCP and thus less cold tolerance, during the coldest season. The suppressed feeding activity under SD conditions would lower the SCP, thereby reducing the possibility of lethal tissue freezing. Such a photoperiodic and thermal regulation of the larval development and the supercooling ability appear to represent adaptive mechanisms for winter survival in this beetle.     

Moulting reduces freeze susceptibility in the Antarctic mite Alaskozetes antarcticus (Michael)

Abstract.  The effect of moulting on the cold hardiness of the oribatid mite Alaskozetes antarcticus (Michael) is investigated. Non moulting animals show clear seasonal patterns of cold hardiness with high supercooling points (SCPs) at the peak of summer and an increasing proportion of low SCPs with declining environmental temperatures. By contrast, both field-fresh and laboratory acclimated (5 °C) mites in the moult state are consistently found to have low SCPs regardless of environmental temperature.     

寄主对桔小实蝇耐寒性的影响

为了研究寄主营养对桔小实蝇耐寒性的作用,测定了以15种果蔬饲养的桔小实蝇1日龄蛹的过冷却点(supercooling points,SCP); 再选取南瓜、西红柿、柑桔、番石榴和杨桃等5种果蔬,测定了桔小实蝇3龄老熟幼虫、1日龄蛹、3日龄蛹、5日龄蛹、7日龄蛹和雌雄成虫的过冷却点,并观察了1日龄蛹的低温存活力。结果表明：（1）15种果蔬饲养所得的桔小实蝇1日龄蛹SCP均值在-11.03℃～-13.17℃,不同寄主发育的桔小实蝇SCP值存在显著性差异,其中以取食蒲桃的最高,为-11.03℃,取食苦瓜的最低,为-13.17℃。（2）5种果蔬饲养所得的桔小实蝇各虫态的SCP均值存在极显著差异(F_(4,863)＝35.6,P<0.01); 同一寄主上的桔小实蝇不同虫态之间SCP均值也达到极显著性差异(F_(6,863)＝392.9,P<0.01); 且寄主和发育龄期之间存在着极显著的交互作用(F_(24,863)＝9.4,P<0.01)。（3）桔小实蝇各发育阶段,SCP值表现一定变化： 老熟幼虫发育至1日龄蛹,SCP值变化不大; 蛹发育至3、5和7天过冷却能力明显增强,降至-20℃左右,但他们之间没有明显区别; 羽化后3～5天的成虫SCP值又升高至-10℃左右。老熟幼虫、1日龄蛹和2～3日龄成虫与3日龄、5日龄和7日龄蛹的SCP值之间有显著性差异。（4）将5种果蔬饲养所得的桔小实蝇1日龄蛹置于6℃和-3℃下进行较长时间(1～8天)和较短时间(1～8 h)的低温处理,发现番石榴、杨桃和南瓜发育的蛹经低温处理后的校正羽化率较西红柿和柑桔发育的蛹高; 同样在0℃、3℃、6℃和9℃处理(2天)的实验中,得出相似的结果。因此,本实验结果表明桔小实蝇幼虫由于生活寄主的不同使得其下一代蛹的耐寒性产生了差异,引起其差异的原因值得进一步研究。