Insect Cold Hardiness Research Articles

Is the strategy for cold hardiness in insects determined by their water balance? A study on two closely related families of beetles: Cerambycidae and Chrysomelidae

The strategy for cold-hardiness and water balance features of two closely related families of Coleoptera, Cerambycidae and Chrysomelidae, were investigated. Cerambycids were freeze-avoiding with low supercooling points, whereas chrysomelids froze at high temperatures and were tolerant to freezing. Hence, the two families have adopted different strategies for cold-hardiness. Due to their low trans-cuticular water permeability, the cerambycids have low rates of evaporative water loss. Chrysomelids have much higher trans-cuticular water permeability, but freezing brings their body fluids in vapour pressure equilibrium with ice and prevents evaporative water loss. The differences in cold-hardiness strategies and rates of water loss are likely to reflect the water content of the diets of the two families. Cerambycids feed on dry wood with low water content, causing a restrictive water balance. Chrysomelids feed on leaves with high water content and may use evaporation through the cuticle as a route of water excretion. Haemolymph ice nucleators help chrysomelids to freeze at a high temperature and thus to maximize the period they spend in the water saving frozen state. The diet-related differences in water balance may be the reason why the two families have developed different strategies for cold-hardiness.

Cold hardiness of insects distributed in the area of Siberian Cold Pole

Cold hardiness of insects distributed in the area of Siberian Cold Pole

Winter climates and coldhardiness in terrestrial insects

Overwintering insects must avoid injury and death from the freezing of tissues and from metabolic disruptions associated with exposure to low, non-freezing temperatures. The winter climates of the world are classified in relation to insect overwintering on the basis of their minimum temperatures and the duration of the winter (when temperatures are below the thermal range for activity and development). Outside the Tropical Wet zone, the severity of exposure to cold (temperature, snowfall, duration of exposure, predictability, variability) can vary from a few days at 0°C to months below -20°C with extremes as low as -60°C. The severity of the temperature exposure may be ameliorated by the selection by insects of overwintering sites (exposed, partly-exposed, protected). The relationships among overwintering habitats, the minimum winter temperature in climatic zones, and the supercooling points (SCP) of over 350 terrestrial insects from published reports were examined. Variability in the SCP among insects within each climatic zone and habitat was wide. Among the freeze-susceptible species that overwintered in exposed or partly-protected habitats the SCP and the cold severity of climate were correlated. This was not the case for insects that overwintered in protected habitats. The SCP's of freeze-tolerant insects were generally higher than the freeze-susceptible insects, and the SCP's were not tightly linked with the cold severity of climatic zone. Insects, both freeze-susceptible and freeze-tolerant, overwintering in exposed habitats had lower SCP's than insects from habitats that offered some protection from ambient temperatures. Thirty-eight species had reports of SCP's for different geographical locations. Although there were occasionally differences in the SCP's, there was no consistent pattern of insects having lower SCP's when overwintering in colder habitats. The incidence of freeze-tolerance was higher in boreal and polar climatic zones than in climatic zones with warmer winters. Holometabola insects had a higher incidence of freeze-tolerance than hemimetabola insects. Suggestions for future research directions are outlined.

Key themes in the study of seasonal adaptations in insects I. Patterns of cold hardiness

Recent work on selected topics of particular interest for understanding insect cold hardiness is reviewed. Themes considered include the dynamic nature of cold hardiness, ice nucleation, connections between cold hardiness and desiccation, rapid cold hardening, seasonal changes in mitochondria, survival in nature, and selection for types of cold hardiness. Such seasonal adaptations have a wider range of components than has often been appreciated, including independently evolved elements. Some specific conclusions are drawn and suggestions are made for future work. Several adaptations, such as rapid cold-hardening and mitochondrial degradation, will probably prove to be much more widespread than has yet been realized. From a general perspective, understanding such diverse components and their differences requires an ecological approach that places the biochemical and timing adaptations in context with habitat conditions and demands related to the stresses of the adverse season, seasons favorable for development and reproduction, and the signals that are available in each habitat to predict future environments. Further understanding therefore depends especially on efforts to analyse the adaptations of individual species in the context of their natural environments.

RAPID COLD HARDENING PROVIDING HIGHER COLD TOLERANCE THAN COLD ACCLIMATION IN THE PINE NEEDLE GALL MIDGE THECODIPLOSIS JAPO‐NENSIS LARVAE*

Abstract The responses of overwintering larvae of the pine needle gall midge Thecodiplosis japonensis Uchida et Inouye to rapid cold hardening and cold acclimation were studied. A rapid cold hardening response is found in the 3rd instar larvae of T. japonensis. When overwintering larvae are transferred directly from 27°C to ‐ 15°C for 3 h, there is only 17.9% survival, whereas exposure to 4°C for 2 h prior to transfer to ‐ 15°C increases survival to 40.0%. The acquired cold tolerance is transient and is rapidly lost (after 15 min at 27°C). Rapid cold hardening is more effective in maintaining larval survival than cold acclimation. Different mechanisms are suggested to regulate the insect's cold hardiness under rapid cold hardening and cold acclimation.

A review of insect survival in frozen soils with particular reference to soil-dwelling stages of corn rootworms

Survival mechanisms of insects that may be subjected to freeze–thaw processes in cold climates are reviewed with particular reference to soil-dwelling stages of corn rootworms. Diapause in corn rootworms is discussed in relation to their origin from tropical regions and adaptation for survival in colder climates. Cold-hardiness in insects is reviewed and discussed in relation to existing knowledge about cold-hardiness in corn rootworms during postdiapause development. Current knowledge of soil temperature effects on corn rootworm overwinter egg survival is summarized. Overwinter mortality to eggs of corn rootworms from the effects of subfreezing soil temperature varies with depth of egg placement, which varies within the top 30 cm of the soil profile in response to availability of soil moisture and presence of drought cracks as oviposition sites. Implications of spatial variability in corn rootworm populations for research on corn rootworm management are discussed in relation to spatially variable environmental factors.

Influence of Thermal Acclimation On the Survival of Sitophilus Granarius (L.) and Oryzaephilus Surinamensis (L.) At Low Temperatures

Low temperatures have been used for many years to control populations of stored-product insects. The aim of aeration was primarily to cool down the grain and then to prevent its deterioration by reducing the number of insects. In Belgium, the mild winters enable insects to survive to the next season. In autumn, the progressive lowering of temperature has an acclimation effect on stored-product insects. The present study was undertaken to determine the survival at low temperatures of non cold-acclimated and laboratory- and field-cold-acclimated insects. We have chosen to work with the granary weevil Sitophilus granarius (L.) and the saw-toothed grain beetle Oryzaephilus surinamensis (L.). They are the most frequent stored-grain pests in Belgium. To compare the cold-hardiness of different laboratory cold-acclimated insects, S. granarius and O. surinamensis were placed at nine different cold-acclimation temperature regimes. Insects were kept at 5°C for 2, 4 and 6 weeks or at -5°C for 4, 7 and 14 days. To assess the field-cold-acclimation in autumn and in winter, insects were monthly taken from a bin and transferred to 5°C for 6 weeks. S. granarius adults were more cold-hardy than O. surinamensis, but O. surinamensis adults compensated their cold-sensibility by a great ability to acclimate. S. granarius is able to survive the winter in Belgium because of its cold-hardiness while O. surinamensis survives because of its ability to acclimate to low temperatures.

The Ecology of Insect Overwintering.

Foreword 1. Introduction 2. The overwintering locale - suitability and selection 3. The stimuli controlling diapause and overwintering 4. Insect cold-hardiness 5. Costs and benefits of overwintering 6. Prediction and control Bibliography Index.

Variation Among Alnus Progenies Grown in Ohio

Seedlings grown in Ohio from seed collected from 12 native seed sources of Alnusglutinosa (European black alder) and one seed source of Alnus cordata (Italian alder) were outplantedin1981 in acombination provenance/family planting. Data were collected over a period of 11 years after planting. Results show highly significant variation among provenances in winter injury, time of growth initiation, rate of survival, leaf miner injury, and height and diameter growth. Italian alder seedlings showed the least leafminer injury and the earliest flushing, but showed the poorest survival of all groups tested, primarily because of winter injury. European black alder seedlings grown from seed collected in Iran also sustained major winter dieback and poor survival. Trees from West Germany, France, Denmark, and Yugoslavia seed sources were fastest-growing, whereas seedlings from some sources in southern Europe (Spain, Italy, Bulgaria) were slowest - growing. The genetic variation shown in this study is sufficient to allow for success in breeding for improved insect resistance, cold hardiness, and growth rate in alder.

Insect Cold-Hardiness: Insights from the Arctic

Cold-hardiness and related adaptations of insects in the Arctic correspond to characteristic climatic constraints. Some species are long-lived and are cold-hardy in several stages. In the Arctic, diapause and cold-hardiness are less likely to be linked than in temperate regions, because life-cycle timing depends as much on the need to coincide development with the short summer as on the need to resist winter cold. Winter habitats of many species are exposed rather than sheltered from cold so that development in spring can start earlier. Several features of cold-hardiness in arctic species differ from the characteristics of temperate species: these include very cold-hardy insects with low supercooling points that are not freezing tolerant; freezing-tolerant species that supercool considerably rather than freezing at relatively high subfreezing temperatures; mitochondrial degradation linked with the accumulation of cryoprotectants; and the possibly limited occurrence of thermal hysteresis proteins in winter. Several interesting relationships between cold-hardiness and water have been observed, including different types of dehydration. Winter mortality in arctic insects appear to be relatively low. Adaptations to cold in summer include retention of cold-hardiness, even freezing tolerance; selection of warm sites; and behaviour such as basking that allows elevated body temperatures. Studies especially on the high-arctic moth Gynaephora groenlandica show that various factors including cold-hardiness and other summer and winter constraints dictate the structure of energy budgets and the timing of life cycles. Future work should focus on the biological and climatic differences between arctic and other areas by addressing habitat conditions, life-cycle dynamics, and various aspects of cryoprotectant production at different times of year. Even in the Arctic cold-hardiness is complex and involves many simultaneous adaptations.Key words: cold-hardiness, insects, supercooling, freezing-tolerance, cryoprotectants, metabolism, energy budgets, life cycles, habitat selection

Insects at Low Temperature: A Predictable Relationship?

In the study of insect ecology it is convenient to classify the factors that determine the abundance of different species. Biotic and abiotic, (physical), density dependent and independent, and climate and competition, are examples of this descriptive terminology. While the value of such a classification is debatable, it is commonly accepted that weather is an important abiotic factor, which normally acts in a density-independent way. When considering the influence of climate on insects, a distinction should be made between effects occurring within and outside of the socalled favourable zone. Within the favourable zone, climate, particularly temperature, determines rate-based processes such as reproduction and development. Conditions outside the favourable zone prevent reproduction and development, and at the extremes, can become lethal (Dempster, 1975). For insects of the temperate region this switch from a favourable to an unfavourable climate is largely a seasonal phenomenon, peaking in summer and winter respectively. Similarly, the nature of the mortality factors acting on insects reflects this seasonal trend, with the effects of natural enemies and competition being most important from late spring to autumn, and low temperature the dominant influence in winter. The damage potential of most pest insects is a function of their abundance at the time when crops are most vulnerable to attack. It is therefore valuable to identify the factors that contribute to the annual cycle of mortality, especially those that might be used to predict patterns of future abundance. Forecasts of the likely migration dates, abundance and outbreak areas of pest species allow rational decisions to be made on the use of insecticides, particularly in years of low pest incidence. The need for predictive models of this type has been highlighted by the aphid and associated virus epidemics which have followed two successive winters with abnormally high temperatures, and the prospect of consistently higher winter temperatures as a result of global warming and climate change. Against this background, this paper outlines current ideas on the cold hardiness of temperate insects, demonstrates the importance of microclimates, and presents evidence to show that for some species, the level of winter survival is the primary determinant of their future abundance. The difficulties of predicting mortality from records of winter temperature and indices of cold hardiness are illustrated by reference to three species with differing levels of cold tolerance.

Surviving the Big Chill: Overwintering Strategies of Aquatic and Terrestrial Insects

The purpose of this paper is to describe the cold-hardiness of aquatic insects and to use the literature to compare physiological and behavioral strategies that aquatic and terrestrial insects use to cope with minimum winter temperatures. In sharp contrast to terrestrial insects, aquatic insects from seven different orders had limited ability to supercool and did so to temperatures of only −3 to −7°C. Inability to supercool may be due to inoculative freezing—the penetration of external ice crystals through pores or orifices of the insect's cuticle. Furthermore, our results suggest that terrestrial adult stages of aquatic insects may have greater capacity to supercool than aquatic stages of the same taxon. Our results and others' suggested that few aquatic species are freeze tolerant, and those that are appear to be restricted to the order Diptera. Consequently, behavioral avoidance of ice or the capacity to remain unfrozen while encased in ice may be particularly important for overwintering aquatic insects. Ecological implications of insect coldhardiness at the individual, population, and community level are discussed for both terrestrial and aquatic insects.

Biochemical adaptation for cold hardiness in insects

Specific biochemical adaptations permit winter survival at subzero temperatures by both freeze-tolerant and freeze-avoiding insects. Common to both survival strategies is the accumulation of high concentrations of polyols, providing deep supercooling point depression for freeze-avoiding forms and regulating cell volume reduction during extracellular freezing in freeze-tolerant insects. Studies in my laboratory have elucidated the molecular mechanisms (temperature effects on enzyme properties, allosteric regulation, reversible protein phosphorylation) that control the massive conversion of glycogen to polyols and, in some species, regulate the differential synthesis of dual polyols. New studies have highlighted the importance of aerobic ATP production for glycerol biosynthesis, suggested the importance of microcompartmentation for optimal conversion efficiency, documented seasonal changes in the capacity for polyol synthesis versus reconversion to glycogen and analysed the role of protein phosphorylation in enzyme regulation during polyol synthesis.

A rapid cold-hardening response protecting against cold shock injury in Drosophila melanogaster

In studies of insect cold-hardiness, the supercooling point (SCP) is defined as the temperature at which spontaneous nucleation of body fluids occurs. Despite having an SCP of -20 degrees C, adults of Drosophila melanogaster did not survive exposure to -5 degrees C, which suggests that cold shock causes lethal injury that is not associated with freezing. If, however, flies were chilled at 5 degrees C, for as little as 30 min, approximately 50% of the flies survived exposure to -5 degrees C for 2h. This capacity to cold-harden rapidly was greatest in 3- and 5-day-old adults. The rapid cold-hardening response was also observed in larvae and pupae: no larvae survived 2 h of exposure to -5 degrees C, whereas 63% pupariated if chilled at 5 degrees C before subzero exposure. Similarly, although exposure of pupae to -8 degrees C was lethal, if pre-chilled at 5 degrees C 22% eclosed. This extremely rapid cold-hardening response may function to allow insects to enhance cold-tolerance in response to diurnal or unexpected seasonal decreases in environmental temperature.

Effects of low temperature on diapausing Aglais urticae and inachis io (Lepidoptera: Nymphalidae): Cold hardiness and overwintering survival

Two species of nymphalid butterflies, Aglais urticae and Inachis io were exposed to four different temperature regimes (10,22, −5°C, and cycling −5 10 ° C ) during diapause to determine patterns of cold hardiness and overwintering survival. Supercooling ability increases in all groups from cessation of feeding to 100 days in diapause, but the lowest temperature regime does not produce the lowest mean crytallisation temperature. Pre and post-diapause feeding reduce supercooling as does surface water. Fresh weight loss follows a temperature-dependent pattern with greatest weight loss at 10°C and least at −5°C in both species. Mortality is highest at 10° accounting for 80% of I. io after 100 days and 75% of A. urticae after 170 days. both groups but in I. io a sharp rise in mortality after 100 days resulted in 65% mortality after 155 days in both regimes. There was no evidence of individuals freezing in the subzero regimes. Initial wet weights of survivors are significantly higher than those of non-survivors at all temperatures. Implications for assessment of cold hardiness in insects are discussed.

Interpretation of laboratory experiments on insect cold hardiness

Interpretation of laboratory experiments on insect cold hardiness

The cold-hardiness of Ctenucha virginica (Lepidoptera: Arctiidae) larvae, a freezing-tolerant species

Typical of a freezing-tolerant species, Ctenucha virginica (Esp.) larvae had supercooling points above −11°C during the winter. For several weeks after the snow melt in the spring, larvae could tolerate freezing at the supercooling point, but lost this ability prior to pupation. However, C. virginica was atypical in that 5 μl samples of haemolymph froze from −13 to −16°C, indicating that haemolymph lacked the potent nucleators seen in other freezing-tolerant insects. The high supercooling points (−5 to −9°C) of feeding larvae were probably due to the presence of nucleators in the gut, as samples of the gut contents froze at similar or higher temperatures than the whole insect. Furthermore, premoult larvae, a developmental stage with a predominantly empty digestive tract, froze at temperatures (−12°C) similar to those of haemolymph samples. In addition to the gut contents, moisture on the surface of larvae may be another important source of nucleators as wet larvae froze at −3°C. Sorbitol and fructose concentrations increased with the onset of winter, but the role of these compounds as cryoprotectants was unclear as their concentrations were not correlated with lower lethal temperatures. Larval mortality evaluated 4 days after the termination of cold stress frequently underestimated total larval mortality. Thus the 24 h period following cold stress used to evaluate damage by most researchers, underestimates cold induced mortality. Cold stress can also have sublethal effects, such as increased larval developmental time, lower pupal weight, reduced fecundity, or higher infertility in survivors. These variables are often neglected in insect cold-hardiness studies, but are of considerable biological importance.

Juvenile hormone: Modulation of cryoprotectant synthesis in Eurosta solidaginis by a component of the endocrine system

The role of juvenile hormone as a possible modulator of insect cold-hardiness has been investigated in the gall fly larvae of Eurosta solidaginis. The 3rd-instar larva is freezing tolerant and survives the rigours of winter by producing carbohydrate cryoprotective agents (i.e. glycerol and sorbitol). Since cold-hardening frequently occurs in conjuntion with developmental processes under endocrine control, a study of these possible interrelationships was made. Third-instar larvae collected during autumn were allatectomized by ligation of the head. Experimental larvae received topical applications of synthetic juvenile hormone, methoprene, a potent juvenile hormone analogue, or precocene II, an anti-juvenoid. Following treatment, all larvae were then subjected to one of two temperature acclimation protocols at 5 or 15°C for up to 5 days. Ligation resulted in a 20% decrease in glycerol and up to a 40% increase in sorbitol levels vs controls following 5°C exposure. At 15°C, deprivation yielded a 13% decrease in glycerol and up to a 47% increase in sorbitol. Ligation resulted in decreased glycerol levels independent of temperature especially in early autumn. Cryoprotectant synthesis/accumulation was responsive to juvenile hormone replacement with peak sensitivity observed in October. Ligated larvae were generally insensitive to juvenile hormone replacement in September and December. These responses were temperature dependent; polyol accumulation was reduced by 50% at +5°C and enhanced by 22% at +15°C (2 and 8 μg glycerol/mg larvae, respectively). This study provides the first evidence suggesting an association between juvenile hormone and regulation of cryoprotectant accumulation in insects.

Physiology of cold tolerance in insects.

From the available experimental data a relatively clear picture can be established with regard to the physiological importance of some of the mechanisms involved in insect cold hardening. In freeze-avoiding insects, all potent ice-nucleating agents are removed or inactivated, leading to a depression of the supercooling points to about 20 degrees C. Accumulation of polyols causes a further depression with a magnitude of about twice the corresponding melting-point depression. Production of thermal hysteresis factors causes a stabilization of the supercooled state. In freeze-tolerant insects, potent ice-nucleating agents are produced in the extracellular body fluid, ensuring a protective extracellular freezing at a few degrees below zero. Accumulation of polyols causes a steep drop in the lethal temperature, due to a reduction of the amount of ice by a colligative mechanism. However, there is still much to be learned about the mechanisms by which ice-nucleating agents, polyols, and thermal hysteresis agents are acting. Furthermore, the regulatory mechanisms involved in the production and elimination of these components from the body fluid of the insects are not understood. Also, when it comes to the influence of environmental factors, like photoperiod and temperature, there is much to be learned. In addition to giving attention to these topics, future research should be focused on the possible role of other factors in cold hardening such as bound water, dehydration, low-molecular-weight solutes other than polyols, and the biochemical mechanisms forming the basis of the seasonal changes in the cold hardiness of insects.

Biochemical correlates to cold hardening in insects

A review of each species discussed or of those reported by other investigators would not at this time provide greater insights into those questions fundamental to understanding low temperature tolerance. The strategies of freezing tolerance/avoidance are heterogeneous and rarely lend themselves to a uniform hypothesis. A number of landmarks in this area have been identified. They include (1) the discovery of glycerol as a natural cryoprotectant and its relationship to frost hardening, (2) studies on the diversity of species demonstrating chill and frost hardiness, (3) cryoprotectant modulation in the frozen state and the attendent maintenance of life processes while frozen, (4) the complexity of multicomponent cryoprotectant systems, and (5) the influence of proteinaceous thermal hysteresis and nucleator agents. The field of insect cold hardiness is proceeding beyond the realm of descriptive studies and will focus more sharply on deductive approaches. Fundamental questions relating to the induction of cold hardiness and the reverse, warm acclimatization, (triggers) require study. Four environmental factors, including temperature, state of hydration, nutrient input (balance), and photoperiod appear critical to hardening. Many species may rely on one or more of these factors and elucidation of trigger mechanisms is essential. In order to understand the functions of the diversity of cryoprotectants and their respective sources, an array of descriptions of biochemical phenomenon in the frozen state will be required. It is known that some species can modulate cryoprotectant levels while frozen. The site(s) of synthesis are unknown as are the mechanisms of transport within the “frozen” system. Would passive distribution phenomena be adequate to explain the bulk transport of cryoprotectants in frozen systems? During the past 5 years, the concepts of proteinaceous agents playing critical roles in the hardening process have been identified. Little is known, however, about the structure of these agents, their mechanisms of action, and the manner in which they integrate with low-molecular-weight protective compounds. Overriding each of the above, are the questions of gene regulation and endocrine control. Is the same endocrine control of carbohydrate metabolism found at 20–30 °C functional at 0, −5, or −40 °C. Interestingly, if asked how a given species of insect survives following a freezing encounter, one can only present a list of theories and correlative data supporting those theories. The puzzle has many more pieces than we provide by measurements of supercooling points and glycerol content.