Cold Tolerance Strategy Research Articles

Cold tolerance strategy, supercooling, and cold hardening in three populations of the jumping spider Phidippus audax (Araneae: Salticidae)

Cold tolerance strategy, supercooling, and cold hardening in three populations of the jumping spider Phidippus audax (Araneae: Salticidae)

Cold tolerance and metabolism of red-haired pine bark beetle Hylurgus ligniperda (Coleoptera: Curculionidae) during the overwintering period.

Hylurgus ligniperda invaded Shandong, China, through imported forest timber, posing a threat to China's forest health. Exotic insects with broad environmental tolerance, including low temperatures, may have a better chance of surviving the winters and becoming invasive. Understanding the cold-tolerance strategies of H. ligniperda may help to design sustainable pest management approaches. In this study, we aim to investigate the cold-tolerance ability and relevant physiological indicators in overwintering H. ligniperda adults to determine any possible overwintering strategies. Supercooling points (SCPs) for adults H. ligniperda differed significantly across months and reached the lowest level in the mid- and post-overwintering period, the minimum SCPs -6.45 ± 0.18 °C. As the cold exposure temperature decreased, the survival rate of adults gradually decreased, and no adult survived more than 1 day at -15 °C, and the LLT50 for 1 day was -7.1 °C. Since H. ligniperda adults can survive internal ice formation, they are freeze-tolerant insects. Throughout the overwintering period, the SCPs and the water, protein, sorbitol, and glycerol content in adults decreased initially and then increased. We reported significant correlations between total protein, sorbitol, trehalose, and glycerol content in the beetles and SCPs. Glycogen, lipid, protein, trehalose, and sorbitol content in adult beetles may directly affect their cold-tolerance capacity and survival during winter. This study provides a physiological and biochemical basis for further study of metabolism and cold-tolerance strategies in H. ligniperda adults, which may help predict population dynamics and distribution potential of pests.

The supercooling point depression is the leading cold tolerance strategy for the variegated ladybug, [Hippodamia variegata (Goezel)

The variegated ladybug, Hippodamia variegata is one of the most effective predators of various pests that hibernate as adult beetles. During the overwintering period from April 2021 to March 2022, we examined the supercooling point (SCP), cold tolerance, and physiological adaptations of beetles in Kerman, Iran. The beetles exhibited their greatest cold tolerance (63.4% after 24h at -5°C) when their SCP was lowest (-23.2°C). Conversely, from April to October 2021, the SCP reached its peak (approximately -13.0°C), while cold tolerance was at its lowest level (6.7% after 24h at -5°C). Cryoprotectant content (trehalose, glycerol, and glucose) was at its highest level in September (11.15, 10.82, and 6.31mg/g, respectively). The critical thermal minimum (CTmin) reached its lowest point of -2.2°C in January and February. The lowest point of the lower lethal temperature (LLT) coincided with the lowest level of the SCP and the highest level of cold tolerance (in February, LT50 = -5.3°C, SCP = -23.2°C, and survival = 77.78% at -4°C/24h). Chill-coma recovery time (CCRT) was examined at five different temperatures and two different exposure durations. The CCRT increased with a decrease in exposure temperature and time (68.0s at -2°C after 2h and 102.0s at -2°C after 4h). As the majority of the overwintering beetle's mortality occurred at temperatures significantly higher than SCP, the adults of H. variegata are chill-susceptible insects that primarily rely on a depressed supercooling point to cope with unfavorable conditions during the overwintering period.

Effects of rapid cold-hardening and cold acclimation on egg survival and cryoprotectant contents in Ceracris kiangsu (Orthoptera: Arcypteridae)

Abstract The bamboo grasshopper, Ceracris kiangsu Tsai, is a serious pest of bamboo in China and Southeast Asia, and it overwinters as eggs for a period of up to 9 mo. Despite its importance, cold tolerance has not been thoroughly examined in this species. Thus, the present study investigated the low-temperature tolerance of overwintering eggs collected in the field, particularly the effects of rapid cold-hardening (RCH) and cold acclimation (ACC) on egg survival, and changes in the cryoprotectant contents. The supercooling point of overwintering eggs collected from the field was −23.9 °C, and their survival rate after exposure to −22 °C for 6 h was 26.6%, thereby suggesting that the cold tolerance strategy employed by C. kiangsu is freeze avoidance. After exposure to 0 and 4 °C for 12 and 24 h, or 0, 4, and 8 °C for 5 days, the survival rate of eggs subjected to −22 °C increased to approximately 50%, with significant effects of RCH and ACC. The glycerol levels in RCH and ACC treated eggs were also significantly higher than those in the control group, but the protein and trehalose contents were either reduced or not significantly altered. These results indicate that glycerol functions as a low molecular weight cryoprotectant in C. kiangsu eggs, and that RCH and ACC treatment facilitate its accumulation, thereby enhancing cold tolerance. Furthermore, the correlation between RCH and ACC was investigated.

Cold tolerance strategy and cryoprotectants of Megabruchidius dorsalis in different temperature and time stresses.

The honey locusts (genus Gleditsia) are a genus of high-value trees in Asia. Seed beetle, Megabruchidius dorsalis (Fåhraeus) (Col.: Chrysomelidae: Bruchinae), is a Gleditsia oligophagous pest that causes severe yield reduction. To understand the cold tolerance of M. dorsalis adults, this study investigated its cold tolerance strategy and the influence of low temperatures on its physiology and biochemistry. The low-temperature treatments were divided into three groups: long-term temperature acclimation (Group 1; 15°C, or 20°C, or 25°C, or 28°C [control check, CK] for 10days), short-term low-temperature exposure (Group 2; 0°C or 4°C for 2h), and long-term low-temperature induction (Group 3; 0°C or 4°C for 1, 3, or 5d). The supercooling point (SCP; temperature at which spontaneous nucleation and ice lattice growth begin), freezing point (FP; temperature at which insect fluids freeze), low lethal temperature (LLT; temperature at which all individuals are killed), water, lipid, glycerol, and total sugars contents were measured under different temperature stresses. The results showed that M. dorsalis adults were a freeze-avoidant species. The SCP and LLT at 28°C were -10.62°C and -19.48°C, respectively. The SCP and FP of long-term temperature acclimation (15°C, or 20°C, or 25°C) were significantly lower than that of the control group (28°C). The water content of the long-term low temperature induction (0°C) group was significantly lower than that of the control group. The lipid and glycerol content in the acclimated group at 20°C and 25°C were significantly higher than in the control group. M. dorsalis adults may maintain their biofluids in a supercooled state via cryoprotectant accumulation and cryoprotective dehydration to prevent ice nucleation. This study provides a theoretical basis for future research on overwintering and potential distribution and related prediction of M. dorsalis adults.

Supercooling points of freeze-avoiding bumble bees vary with caste and queen life stage

Bumble bees thrive in cold climates including high latitude and high altitude regions around the world, yet cold tolerance strategies are largely unknown for most species. To determine bumble bee cold tolerance strategy, we exposed bumble bees to a range of low temperatures and measured survival 72 h post-exposure. All bees that froze died within 72 h while only one bee died without freezing, suggesting that bumble bees are generally freeze-avoiding insects and may be slightly chill susceptible. We then assessed whether temperatures that cause internal ice formation (supercooling points, SCP) varied among bumble bee castes (drones, workers, and queens), or across queen life stages, collection elevation, species, or season. Males froze at significantly lower temperatures than workers or queens. Queens in pre-overwintering or overwintering states froze at significantly lower temperatures than queens stimulated to initiate ovary development by CO2 narcosis (i.e., “spring” queens). We also tested whether the presence of water (i.e., wet or dry) or ramping rate affected SCP. As expected, queens inoculated with water froze at significantly higher temperatures than dry queens. SCP tended to be lower, but not significantly so, at faster ramping rates (0.5 °C/min vs 0.25 °C/min). We also found no differences in SCP between queen bumble bees collected in spring and fall, between queens collected at two sites differing in elevation by 1100 m, or between three field-caught bumble bee species. Bumble bees appear to have relatively high, invariable SCPs, likely making them highly susceptible to freezing across all seasons. As bumble bees are not freeze-tolerant and appear to lack the ability to prevent freezing at temperatures much below 0 °C, they may rely on season- and caste-specific micro-habitat selection to thrive in cold climates.

Differential of three fields grown Juniperus species summer drought and cold hardening

Background: Understanding species’ reactions to environmental stressors (cold and drought) and characterizing drought tolerance can help us understand their ecosystem responses related to global change. This study aimed to understand and compare the drought and cold tolerance strategies of Juniperus excelsa, Juniperus foetidissima, and Juniperus oxycedrus, which are found in the Western Mediterranean Region. Water relation parameters [ΨTLP (osmotic potential at turgor loss point), Ψ100 (osmotic potential at full turgor), Ɛmax (bulk modulus of elasticity), V0/DW (symplastic water at the saturated point per dry weight of the shoot), RWC (relative water content)] in summer and winter were determined. Total soluble sugar and photosynthetic pigment content were identified in spring, summer, autumn, and winter. Results: J. foetidissima had lower Ψ TLP and higher Ɛmax in summer than other species. The species had similar Ψ TLP 1 Ψ 100 1 Ɛmax, V0/DW, and RWC in winter. A seasonal change was observed in total soluble sugar and photosynthetic pigment content. Total soluble sugar and photosynthetic pigment contents were related to mean air temperature and total precipitation. Conclusion: J. foetidissima was more tolerant to water deficit in the summer, whereas the three species reacted similarly to the cold in the winter.

Cold tolerance of laboratory-reared Asian longhorned beetles

Low winter temperatures in temperate climates can limit the success of non-native species. The Asian longhorned beetle, Anoplophora glabripennis, is an invasive wood-boring pest of hardwood trees in North America and Europe. Native A. glabripennis populations are spread across several climate zones in China and the Korean Peninsula and are likely to encounter low temperatures in at least some of this range. Understanding the lethal limits of the overwintering life stages of A. glabripennis is essential for accurately modeling the risk that invasive populations pose to non-native environments. In this study, we provide the first systematic characterization of the cold tolerance strategy and lower lethal limits of A. glabripennis eggs, larvae, and pupae. In diapausing larvae, the most common overwintering stage in this species, we measure hemolymph glycerol and osmolality and identify the effects of prolonged low temperature exposure. In developing pupae, we identify sublethal effects caused by low temperature exposure before freezing. Eggs and larvae were the most cold-tolerant life stages; eggs were freeze-avoidant with an average supercooling point of −25.8 °C and larvae were freeze tolerant with an LT90 of −25 °C. Hemolymph osmolality of freeze-tolerant larvae, on average, increased to 811 mOsm during chilling. This increase was primarily driven by a concurrent, average increase of 232 mM hemolymph glycerol. Pupae died upon exposure to freezing temperatures, but accumulate strong sublethal effects prior to freezing, indicating that they are chill susceptible. Taken together, these data will be useful to inform species distribution modeling in A. glabripennis.

Expanded Supercooling Capacity With No Cryoprotectant Accumulation Underlies Cold Tolerance of the European Grapevine Moth

The European grapevine moth, Lobesia botrana (Denis et Schiffermuller), is a serious invasive pest that causes significant losses to the flowers and fruits of grapes in most of the world. This multivoltine pest passes the winter as the third-generation diapausing pupa. The current study was designed to compare nondiapausing (first and second generations) and diapausing pupae (third generation) and to investigate the relationship among cold tolerance, the supercooling point (SCP), and diapause development of the third-generation diapausing pupae. The lethal temperatures (LTs) for the three generations were determined using 24-h exposure at subzero temperatures. The mean SCP of the pupae was estimated at approx. -22.6°C, the lowest level of which (-23.7°C) was recorded in the well-developed diapausing pupae in February. The highest level of cold tolerance was also recorded in February. There were no significant differences among the temperatures required to kill 30, 50, and 90% of the pupae. The temperatures significantly decreased from October onward and reached the lowest levels in February during which the lowest SCP and the highest cold tolerance were observed in the diapausing pupae. No significant differences were found in the cryoprotectant levels, among the diapausing and nondiapausing pupae, and the diapause development. The highest activity of cAMP-dependent protein kinase (AMPK) was recorded in the late diapause in February. The findings suggested a relationship among SCP depression, cold tolerance enhancement, and diapause development. A bimodal cold-tolerance strategy (freeze-intolerant and freeze-tolerant) was found to be a feature of the pupae.

Overwintering Larval Cold Tolerance of Sirex noctilio (Hymenoptera: Siricidae): Geographic Variation in Northeast China

Simple SummaryThe cold tolerance strategy of Sirex noctilio overwintering larvae was freeze-avoidance and their supercooling points adjusted seasonally to avoid icing damage. The cold hardiness between different populations varied on a spatiotemporal scale; specifically, the harsher the environment, the stronger the cold tolerance of overwintering Sirex noctilio larvae. A tunnel played a certain protective role but did not affect the low temperature parameters limiting the distribution of S. noctilio. We provide experimentally determined low temperature limiting parameters of Sirex noctilio and prove it has the opportunity to spread and colonize in other regions.Sirex noctilio (Hymenoptera: Siricidae) is an invasive pest that has spread and established in many regions worldwide. However, its cold tolerance strategy is still unclear. We measured the supercooling point (SCP) and the lower lethal temperature (LLT) of overwintering S. noctilio larvae during three overwintering periods in four geographically separated populations in China. In addition, using the statistical analysis of the local historical temperature data, we also conducted comprehensive studies of S. noctilio cold tolerance variations and strategies. We measured the SCP of all samples as S. noctilio could survive at its SCP during a short period of exposure (<48 h) and its cold tolerance strategy was freeze-avoidance. The average SCPs of the groups in different spatiotemporal scales were significantly related to average temperature variation with most individuals exhibiting stronger cold hardiness at low ambient temperatures. S. noctilio exhibited a strong cold tolerance and it has the ability to withstand lower temperatures in cold environments. The geographic population showed a positive tendency as the ambient temperature decreased, which would increase its chance of developing in cold regions.

Morphological response of the red palm weevil, Rhynchophorus ferrugineus, to a transient low temperature analyzed by computer tomography and holographic microscopy.

The red palm weevil (RPW), Rhynchophorus ferrugineus, is one of the worst palm pests worldwide. Our study aims to assess its internal and external morphological response to a sudden but transient decrease in the environmental temperature. Wild pre-pupae were subjected for 7 days to either low (5.0±0.5°C) or ambient temperature (23±1°C). Such conditions mimic a thermal anomaly happening in the larval stage most exposed to environmental factors. We quantified the changes undergone at: 1) the internal morphology, by X-Ray Computer Tomography (CT); 2) the 3-D integument' architecture, by Digital Holographic Microscopy (DHM); and 3) the glucose in hemolymph as a potential endogenous cryoprotectant. From X-ray CT we found that both pre-pupae subjected to cold and those remaining at ambient temperature follow a development where their fat body content decreases while a thick and dense cuticle is formed. There was no difference between both groups in the rate of change of fat body/dense tissues. Nevertheless, the cold group presents a slight developmental delay at the level of hemolymph content. Through DHM we again obtained that pre-pupae subjected to cold have not experienced a stop in their development. However, a more obvious developmental delay is now observed in this group at the level of the integumental roughness. Finally, regarding glucose, we found similar levels in control and ambient temperature larvae, while it was clearly increased in 51,7% of those subjected to cold. Our whole results provide morphological and biochemical evidence showing that the larval-pupal transition of the RPW continues almost undisturbed even during the quiescent state induced by a sudden and severe cold event. Nevertheless, a certain developmental delay is observed in both internal and external morphology. Additionally, the increased glucose level only found in the cold group suggests that glucose is part of the RPW cold tolerance strategy.

Identification of Quantitative Trait Loci for Spikelet Fertility at the Booting Stage in Rice (Oryza sativa L.) under Different Low-Temperature Conditions

Cold stress in rice is a critical factor limiting growth and yield in temperate regions. In this study, we identified quantitative trait loci (QTL) conferring cold tolerance during the booting stage using a recombinant inbred line population derived from a cross between a cold-susceptible Tongil-type cultivar Milyang23 and a cold-tolerant japonica cultivar Giho. A phenotypic evaluation was performed in a cold-water-irrigated field (17 °C) and a temperature-controlled (17 °C/17 °C air and water) greenhouse at the booting stage. Four QTL, including two on chromosome 1 and one each on chromosomes 6 and 9, were identified in the cold-water-irrigated field, with an R2 range of 6.3%–10.6%. Three QTL, one on each of chromosomes 2, 6 and 9, were identified under the temperature-controlled greenhouse condition, with an R2 range of 5.7%–15.1%. Among these, two QTL pairs on chromosomes 6 (qSFF6 and qSFG6) and 9 (qSFF9 and qSFG9) were detected in the cold treatments of both field and greenhouse screenings. Our results provide a reliable dual-screening strategy for rice cold tolerance at the booting stage.

Overwintering Physiology and Cold Tolerance of the Sunn Pest, Eurygaster integriceps, an Emphasis on the Role of Cryoprotectants.

As a serious pest of wheat, the Sunn pest, Eurygaster integriceps Puton (Hem.: Scutelleridae), is prevalent in Iran. This pest belongs to univoltine species and tends to estivate and overwinter in high altitudes of nearby mountains as diapausing adults. The economic importance of the crop was attacked by this pest, i.e., wheat led the authors to study the physiological adaptations of these diapausing adults, that is, changes in the supercooling point (SCP), in the accumulation of cryoprotectants, and in the activities of the related enzymes in relation to diapause development. The mean SCP of the diapausing adults was found to be −8°C. The lowest SCP, i.e., approximately −11°C, was observed in the middle of diapause, October, when the highest cold hardiness was also interestingly recorded. This finding proposed that SCP depression could be a feasible cold-tolerance strategy for diapausing adults. The sugar content was high in the initiation and at the termination of diapause and was low during diapause maintenance. These sugar reserves were most likely utilized to be converted to glycogen and lipid during diapause maintenance as a survival strategy. The changes in the glycogen and lipid contents were inversely proportional to the changes in the total sugar content. The authors also found that the changes in the glycogen content were directly proportional to those in the low-molecular-weight carbohydrates (e.g., glycerol and trehalose) and in the diapause development. This finding underlined the role of the low-molecular-weight carbohydrates, such as the cryoprotectants, in enhancing the cold tolerance of the given insect. In this study, the diapause-associated changes in the activities of α-amylases and proteases were also investigated. The results showed that the enzyme activities were related to diapause development and cold-tolerance enhancement. The highest enzyme activity was observed in September. Since the overwintering adults of the Sunn pest could not tolerate temperatures below their SCPs, they were grouped in the freeze-intolerant species.

Cold tolerance strategy and cold hardiness of the invasive zigzag elm sawfly Aproceros leucopoda (Hymenoptera: Argidae)

Abstract The invasive sawfly Aproceros leucopoda causes severe defoliation of various elm species and thus can be a major pest in forest stands and urban environments. The overwintering biology of A. leucopoda has not been investigated so far; therefore, the aim of this study was to determine the cold tolerance strategy and cold hardiness of hibernating A. leucopoda eonymphs. The supercooling points (SCPs) of overwintering individuals varied geographically, monthly and interannually and ranged between −12.14 °C and −24.22 °C. As none of the eonymphs survived once the SCP had been reached, A. leucopoda is classified as a freeze‐avoidant species. Survival rates of overwintering eonymphs exposed to different sub‐zero temperatures above the SCP (−1.6 °C and −4.0 °C for 10, 20 and 30 days and −10.5 °C for 9 days) ranged between 89.2% and 100%, suggesting that A. leucopoda is not a chill‐susceptible species. Our results suggest that low winter temperatures may not be expected to be an important limiting factor for the overwintering success of A. leucopoda.

A comparison of low temperature biology of Pieris rapae from Ontario, Canada, and Yakutia, Far Eastern Russia

Low temperatures limit the distribution and abundance of ectotherms. However, many insects can survive low temperatures by employing one of two cold tolerance strategies: freeze avoidance or freeze tolerance. Very few species can employ both strategies, but those that do provide a rare opportunity to study the mechanisms that differentiate freeze tolerance and freeze avoidance. We showed that overwintering pupae of the cabbage white butterfly Pieris rapae can be freeze tolerant or freeze avoidant. Pupae from a population of P. rapae in northeastern Russia (Yakutsk) froze at c. −9.3 °C and were freeze-tolerant in 2002–2003 when overwintered outside. However, P. rapae from both Yakutsk and southern Canada (London) acclimated to milder laboratory conditions in 2014 and 2017 froze at lower temperatures (< −20 °C) and were freeze-avoidant. Summer-collected P. rapae larvae (collected in Yakutsk in 2016) were partially freeze-tolerant, and decreased the temperature at which they froze in response to starvation at mild low temperatures (4 °C) and repeated partial freezing events. By comparing similarly-acclimated P. rapae pupae from both populations, we identified molecules that may facilitate low temperature tolerance, including the hemolymph ice-binding molecules and several potential low molecular weight cryoprotectants. Pieris rapae from Yakutsk exhibited high physiological plasticity, accumulating cryoprotectants and almost doubling their hemolymph osmolality when supercooled to −15 °C for two weeks, while the London P. rapae population exhibited minimal plasticity. We hypothesize that physiological plasticity is an important adaptation to extreme low temperatures (i.e. in Yakutsk) and may facilitate the transition between freeze avoidance and freeze tolerance.

Overwintering Red Velvet Mites Are Freeze Tolerant.

Although many arthropods are freeze tolerant (able to withstand internal ice), small-bodied terrestrial arthropods such as mites are thought to be constrained to freeze avoidance. We field-collected active adult red velvet mites, Allothrombium sp. (Trombidiidae), in winter in Southwestern Ontario, Canada, where temperatures drop below -20°C. These mites froze between -3.6° and -9.2°C and survived internal ice formation. All late-winter mites survived being frozen for 24 h at -9°C, and 50% survived 1 wk. The lower lethal temperature (LLT50; low temperature that kills 50% of mites) was ca. -20°C in midwinter. Hemolymph osmolality and glycerol concentration increased in midwinter, accompanied by decreased water content. Thus, this species is freeze tolerant, demonstrating that there is neither phylogenetic nor size constraint to evolving this cold tolerance strategy.

The springtail Megaphorura arctica survives extremely high osmolality of body fluids during drought.

The springtail Megaphorura arctica Tullberg 1876 is widespread in the arctic and subarctic regions where it can be abundant along beaches. This species survives winters using cryoprotective dehydration as a cold tolerance strategy during which it becomes drastically dehydrated. Several studies have investigated the physiological responses associated with water loss of M. arctica under exposure to freezing temperatures, but little is known of the dynamics of body water and hemolymph osmolality when subjected to gradually increasing drought stress at temperatures above the freezing point. Therefore, an experiment was conducted in which M. arctica was subjected to relative humidities (RH) decreasing from fully saturated conditions to ca. 89%RH over a period of 30 days. During the experiment water content of springtails decreased from about 3 to ca. 0.5mgmg-1 dry weight. Alongside with water loss, trehalose concentrations increased from nearly nothing to 0.12mg mg-1 dry weight, which contributed to an increase in hemolymph osmolality from ca. 250mOsm to at least 7Osm. All springtails survived water loss down to 0.7mgmg-1 dry weight and hemolymph osmolality of ca. 4Osm, and about 60% of the springtails survived with only 0.5mg watermg-1 dry weight and osmolality of ca. 7Osm.At this level of dehydration, Differential Scanning Calorimetry analysis showed that most, but not all, osmotically active water was lost. It is discussed that the extensive dehydration must be associated with high concentrations of salts potentially causing denaturation and precipitation of cellular proteins. M. arctica is remarkably tolerant of dehydration, but because it does not endure loss of the osmotically inactive water it cannot be categorized as a truly anhydrobiotic species.

Modest Effects of Host on the Cold Hardiness of Emerald Ash Borer †

The emerald ash borer, Agrilus planipennis Fairmaire, is invading North America and Europe but has not yet reached its ultimate distribution. Geographic differences in host availability and winter temperatures might affect where this species will occur. In central North America, black ash (Fraxinus nigra) is more abundant than green ash (F. pennsylvanica) at northern latitudes, but much of our current understanding of A. planipennis cold tolerance is based on observations of overwintering larvae from green ash. The effects of black and green ash on the cold hardiness of A. planipennis larvae were measured over three winters. Supercooling point, the temperature at which insect bodily fluids spontaneously begin to freeze, was marginally greater for larvae from artificially-infested black ash than green ash in one trial, but not in three others. Host species also did not consistently affect mortality rates after larval exposure to subzero temperatures, but larvae from black ash were less cold hardy than larvae from green ash when there were differences. Comparisons of mortality rates among chilled (unfrozen) and frozen larvae indicated that overwintering A. planipennis larvae are primarily freeze avoidant, and this cold tolerance strategy is unaffected by host. All of our studies suggest that A. planipennis larvae from black ash are not more cold hardy that larvae from green ash. Where temperatures annually decline below ~−30 °C, overwintering morality may substantially affect the population dynamics and future impacts from this invasive alien species.

Mechanisms underlying insect freeze tolerance.

Freeze tolerance - the ability to survive internal ice formation - has evolved repeatedly in insects, facilitating survival in environments with low temperatures and/or high risk of freezing. Surviving internal ice formation poses several challenges because freezing can cause cellular dehydration and mechanical damage, and restricts the opportunity to metabolise and respond to environmental challenges. While freeze-tolerant insects accumulate many potentially protective molecules, there is no apparent 'magic bullet' - a molecule or class of molecules that appears to be necessary or sufficient to support this cold-tolerance strategy. In addition, the mechanisms underlying freeze tolerance have been minimally explored. Herein, we frame freeze tolerance as the ability to survive a process: freeze-tolerant insects must withstand the challenges associated with cooling (low temperatures), freezing (internal ice formation), and thawing. To do so, we hypothesise that freeze-tolerant insects control the quality and quantity of ice, prevent or repair damage to cells and macromolecules, manage biochemical processes while frozen/thawing, and restore physiological processes post-thaw. Many of the molecules that can facilitate freeze tolerance are also accumulated by other cold- and desiccation-tolerant insects. We suggest that, when freezing offered a physiological advantage, freeze tolerance evolved in insects that were already adapted to low temperatures or desiccation, or in insects that could withstand small amounts of internal ice formation. Although freeze tolerance is a complex cold-tolerance strategy that has evolved multiple times, we suggest that a process-focused approach (in combination with appropriate techniques and model organisms) will facilitate hypothesis-driven research to understand better how insects survive internal ice formation.

Elusively overwintering: a review of diamondback moth (Lepidoptera: Plutellidae) cold tolerance and overwintering strategy

AbstractThere is no consensus on the overwintering strategy used by the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae). As a result, the topic of diamondback moth overwintering in temperate climates remains controversial. However, there has been general agreement that the diamondback moth does not overwinter in diapause. This review compiles data on low temperature survival to determine cold tolerance mechanisms and the cold tolerance strategy of the diamondback moth. According to cold tolerance data and observations from key overwintering studies in eastern North America, the diamondback moth likely overwinters in a quiescent state in no specific overwintering stage and is chill susceptible. Observations from key overwintering studies suggest a northern overwintering limit for diamondback moth of ~43°N in eastern North America. Climate change may alter winter conditions in temperate climates, making temperate regions susceptible to potential diamondback moth overwintering and recurring outbreaks.