Insect Cold Hardiness Research Articles

Lysine Methylation and Histone Modifications during Cold Stress of Insects: Freeze-Tolerant Eurosta solidaginis and Freeze-Avoiding Epiblema scudderiana.

Overwintering survival by insects, whether of the freeze-tolerant or freeze-avoiding types, is typically associated with a strong suppression of metabolic rate (e.g., entry into diapause) that involves the differential expression of many genes with regulation at the transcriptional, translational or post-translational levels. Epigenetic modifications have been suggested to play a vital role in regulating cold responses of insects. However, knowledge of the roles of epigenetic mechanisms in modulating gene expression for winter survival of the larvae of two goldenrod gall formers, the freeze-tolerant dipteran Eurosta solidaginis and the freeze-avoiding lepidopteran Epiblema scudderiana, remain unknown. The current study evaluates the role of cold-induced lysine methylation and histone modifications, with enzymes of lysine methylation (SETD8, SETD7, SUV39H1, SMYD2 and ASH2L), as well as relative levels of histone H3 acetylation (H3K9ac, H3K18ac, H3K27ac, H3K56ac) and methylation (H3K4me1, H3K9me3, H3K36me2) examined in two insects. Significant (p < 0.05) reductions were observed in most of the targets of histone methylation/acetylation for decreasing temperatures of Ep. scudderiana larvae, whereas selected histone methylation/acetylation targets were conversely elevated (p < 0.05) in E. solidaginis, particularly under conditions of 5 °C for 4 h. Histone H3 expression was found to be variable without statistical differences in larval goldenrod gall moths and gall flies. These results provide basic information on the patterns of epigenetic regulation involved in insect cold hardiness.

Testing of arctic insect hemolymph as a secondary agent in applied cryopreservation

BACKGROUND: Cold hardiness of insects from extremely cold regions is based on a principle of natural cryoprotection, which is associated with physiological mechanisms provided by cryoprotectants. OBJECTIVE: Since arctic cold-hardy insects are producers of highly effective cryoprotectants, in this study, the hemolymph of Aporia crataegi L. and Upis ceramboides L. from an extremely cold area (Yakutia) was tested as a secondary component of cryoprotective agents (CPA) for cryopreservation (−80°C) of human peripheral blood lymphocytes and skin fibroblasts. MATERIALS AND METHODS: Lymphocytes and skin fibroblasts were treated with various combinations of DMSO and hemolymph extract and step-wise cooled to −80°C. Post-cryopreservation cell viability was assessed by vital staining and morphological appearance. RESULTS: Viability was higher when cells were frozen with a mixture containing DMSO and Upis ceramboides hemolymph compared to the cells frozen in DMSO, while cells frozen with DMSO and Aporia crataegi hemolymph did not survive. The fact that hemolymph of not every cold-resistant insect can be used as a secondary agent along with DMSO indicates that only a unique combination of hemolymph components and its compatibility with cells might result in a positive effect. CONCLUSION: Although the use of insect hemolymph as a complementary agent in applied cryopreservation is a problem in terms of practical application, such studies could initiate new trends in the search for the most successful hemolymph-like cryoprotectant systems.

Effect of gamma irradiation and subsequent cold storage on the development and predatory potential of seven spotted ladybird beetle Coccinella septempunctata Linnaeus (Coleoptera; Coccinellidae) larvae

Seven spot ladybird beetle, (Coccinella septempunctata) is a widely distributed natural enemy of soft-bodied insect pests especially aphids worldwide. Both the adult and larvae of this coccinellid beetle are voracious feeders and serve as a commercially available biological control agent around the globe. Different techniques are adopted to enhance the mass rearing and storage of this natural enemy by taking advantage of its natural ability to withstand under extremely low temperatures and entering diapause under unfavorable low temperature conditions. The key objective of this study was to develop a cost effective technique for enhancing the storage life and predatory potential of the larvae of C. septempunctata through cold storage in conjunction with the use of nuclear techniques, gamma radiations. Results showed that the host eating potential of larvae was enhanced as the cold storage duration was increased. Gamma irradiation further enhanced the feeding potential of larvae that were kept under cold storage. Different irradiation doses also affected the development time of C. septempuntata larvae significantly. Without cold storage, the lower radiation doses (10 and 25 GY) prolonged the developmental time as compared to un-irradiated larvae. Furthermore, the higher dose of radiation (50GY) increased the developmental time after removal from cold storage. This study first time paves the way to use radiation in conjunction with cold storage as an effective technique in implementation of different biological control approaches as a part of any IPM programs

Cold Hardiness of the Black Soldier Fly (Diptera: Stratiomyidae).

The black soldier fly, Hermetia illucens (L.), shows potential as a resource for animal feed. However, industrial production in regions where the insect is not native, like northwestern Europe, could lead to permanent establishment, which might entail environmental risks. In temperate climates, establishment depends on the insect's ability to overwinter. This study assessed the insect's cold hardiness by determining the supercooling point (SCP) and lower lethal time at 5 °C (LTime10,50,90) for different life stages. As diet or acclimation can influence cold hardiness, prepupae reared on different substrates and acclimated prepupae were tested in separate experiments. The SCP ranged from -7.3 °C for late-instar larvae to -13.7 °C for pupae. Prepupae reared on a highly nutritional substrate had a lower SCP compared with a control diet composed of chicken feed (-14.1 °C vs. -12.4 °C, respectively), whereas the SCP was unaffected by acclimation. Based on the LTime, prepupae and pupae were the most cold hardy life stages. Acclimated prepupae were most cold tolerant, with a LTime50 of 23 d. Based on an empirical relationship between LTime50 and field survival of various arthropods, it was predicted that H. illucens would survive about 47 d in the field during northwestern European winters. The results from this laboratory study suggest that H. illucens is rather unlikely to overwinter in northwestern Europe. However, caution is warranted given that diet and acclimation can influence the insect's cold hardiness and in the field the insect may survive in a diapausing state or in protected hibernacula.

Elevated chaperone proteins are a feature of winter freeze avoidance by larvae of the goldenrod gall moth, Epiblema scudderiana

Winter survival for many insect species includes a need to maintain metabolic homeostasis and structural/functional integrity of macromolecules not only over a wide range of cold temperatures but also in response to rapid temperature change. Chaperones are well-known to protect/stabilize protein structure with regard to heat stress but less is known about their potential involvement in long-term protection of the proteome at subzero temperatures. The present study assessed the participation of chaperone proteins in the cold hardiness of larvae of the goldenrod gall moth, Epiblema scudderiana (Clemens) (Lepidoptera, Olethreutidae), monitoring changes in nine proteins over the winter months as well as their responses to laboratory cold acclimation or anoxia exposure. Four heat shock proteins (HSPs: Hsp110, Hsp70, Hsp60, Hsp40), three glucose-regulated proteins (GRPs: Grp78, Grp 94, Grp170) and the tailless complex polypeptide 1 (TCP-1) as well as the heat shock transcription factor (HSF1) were investigated. In general, all were significantly elevated in larvae collected from an outdoor site between October and March, as compared with September values, and chaperone levels were reduced again in April. The October to March interval also includes the period of diapause followed by cold quiescence in the species. Relative expression of Hsp70, Hsp60 and Hsp40 rose by 2–3-fold, GRPs increased 1.5–3-fold, and levels of active (hyperphosphorylated) HSF1 increased by 4–4.8-fold over the midwinter months. Chilling from 15°C to 4°C in the laboratory upregulated Grp78 protein content that remained high as temperature was further reduced to −4°C and then −20°C whereas Hsp110, Hsp70 and HSF1 levels increased when larvae were exposed to −4°C and −20°C. Grp170 (also known as oxygen-regulated protein 150) was the only chaperone that increased significantly in the larvae in response to anoxia exposure at 4°C. The data also indicated that multiple subcellular compartments received enhanced protection for their proteome since upregulation of chaperones included proteins known to occur in cytosolic (Hsp40, Hsp70), mitochondrial (Hsp60) and endoplasmic reticulum (Grp170) locations. Overall, the data indicate that chaperones have a significant role to play in the winter cold hardiness of E. scudderiana and identify declining temperatures (and perhaps also oxygen restriction) as potential modulators of chaperone production. The data add support to a relatively understudied area of insect cold hardiness – the long-term protection and stabilization of the proteome over the winter months.

Insect cold hardiness: the role of mitogen-activated protein kinase and Akt signalling in freeze avoiding larvae of the goldenrod gall moth, Epiblema scudderiana.

Larvae of the goldenrod gall moth, Epiblema scudderiana, use the freeze avoidance strategy of cold hardiness to survive the winter. Here we report that protein kinase-dependent signal transduction featuring mitogen-activated protein kinase (MAPK) signalling cascades (extracellular signal regulated kinase, c-jun N-terminal kinase and p38 MAPK pathways) and the Akt (also known as protein kinase B, or PKB) pathway could be integral parts of the development of cold hardiness by E. scudderiana. We used Luminex technology to assess the protein levels and phosphorylation status of key components and downstream targets of those pathways in larvae in response to low temperature acclimation. The data showed that MAPK pathways (both total protein and phosphorylated MAPK targets) were inhibited after 5°C acclimation, but not -15°C exposure, as compared with the 15°C control group. However, total heat shock protein 27 (HSP27) levels increased dramatically by ∼12-fold in the -15°C acclimated insects. Elevated HSP27 may facilitate anti-apoptotic mechanisms in an Akt-dependent fashion. By contrast, both 5 and -15°C acclimation produced signs of Akt pathway activation. In particular, the inhibitor phosphorylated Glycogen Synthase Kinase 3a (p-GSK3) levels remained high in cold-exposed larvae. Additionally, activation of the Akt pathway might also facilitate inhibition of apoptosis independently of GSK3. Overall, the current study indicates that both MAPK and Akt signal transduction may play essential roles in freeze avoidance by E. scudderiana.

Differential expression and emerging functions of non-coding RNAs in cold adaptation.

Several species undergo substantial physiological and biochemical changes to confront the harsh conditions associated with winter. Small mammalian hibernators and cold-hardy insects are examples of natural models of cold adaptation that have been amply explored. While the molecular picture associated with cold adaptation has started to become clearer in recent years, notably through the use of high-throughput experimental approaches, the underlying cold-associated functions attributed to several non-coding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), remain to be better characterized. Nevertheless, key pioneering work has provided clues on the likely relevance of these molecules in cold adaptation. With an emphasis on mammalian hibernation and insect cold hardiness, this work first reviews various molecular changes documented so far in these processes. The cascades leading to miRNA and lncRNA production as well as the mechanisms of action of these non-coding RNAs are subsequently described. Finally, we present examples of differentially expressed non-coding RNAs in models of cold adaptation and elaborate on the potential significance of this modulation with respect to low-temperature adaptation.

Relative male and female contributions to the supercooling point of their offspring in Microvelia reticulata (Heteroptera: Veliidae)

AbstractCold hardiness is a key life history trait in temperate and polar ectothermic species, as it affects survival during overwintering, but its evolution is poorly understood. While many studies of cold hardiness in insects have shown differences between species, populations or developmental stages, data on the relative contribution of individual genotypes to cold hardiness are scarce and mainly limited to drosophilid fly species. We used a sib‐analysis (paternal half‐sib/full‐sib breeding design) to estimate the relative contributions of parental generation to the supercooling point (SCP) of the offspring of a heteropteran non‐model insect species, Microvelia reticulata (Heteroptera: Gerromorpha: Veliidae). We found that parent identity affected significantly SCP values of their offspring. Magnitudes of estimated sire and dam variance components were similar but the distributions of individual contributions to SCP differed between sires and dams, which points to sex‐specific genetic or parental effects on SCP in this species. The animal model failed to find a realistic estimate of heritability (h2) of SCP, suggesting that the underlying genetics of SCP in M. reticulata can not be characterized by purely additive effects.

Expression of miRNAs in response to freezing and anoxia stresses in the freeze tolerant fly Eurosta solidaginis

Insect cold hardiness is associated with substantial metabolic rate suppression, often including developmental diapause as well as metabolic suppression imposed by freezing and freeze-associated oxygen limitation. MicroRNAs, small non-coding transcripts that bind to mRNA, are known modulators of hypometabolism in freeze tolerant insects. To further contribute to the growing signature of stress-responsive miRNAs, this study amplified and quantified changes in the expression levels of four microRNA species, miR-8, miR-9, miR-92b and miR-277, in response to freezing or anoxia exposures of freeze tolerant gall fly larvae, Eurosta solidaginis. MiR-92b levels were significantly elevated by 1.57-fold in frozen E. solidaginis at −15°C as compared with 5°C controls, whereas miR-92b levels were significantly reduced in anoxic E. solidaginis to levels that were 0.77-fold as compared with larvae held under normoxic conditions. The other miRNAs investigated showed no significant changes in stressed larvae. These data demonstrate differential miR-92b expression in frozen/anoxic versus control insect larvae and position this miRNA as a stress responsive marker in this model insect.

On the Question of Parameters for Evaluating Cold Hardiness of Freeze Tolerant Insects

The super cooling point (SCP) is the best documented parameter for describing the ability of insects to survive freezing but its value as a predictor of overwintering survival or for estimation of the cold hardiness potential, is limited. According to this study, the SCP is influenced by such factors as polyol and protein concentration in the hemolymph; therefore it can be lower in winter than it is in spring. Nevertheless the quality of ice nucleating process is higher in winter insects due to which insects survive the lowest winter temperatures. The depletion of polyols in spring causes increase of SCP. Unlike in the autumn, when an increase in SCP is associated with development of freeze tolerance, spring changes in SCP of the insects occur simultaneously with loss of cold tolerance. The present study on the freezetolerant Upis ceramboides inhabiting central Yakutia (Eastern Siberia, Russia) shows that SCP itself is not a sufficiently appropriate parameter for evaluation of insect cold hardiness. For these purposes it should be used together with other criteria, such as specific ice nucleating activity and profile of ice nucleating activity

Short communication. Impact of the amino acid proline on the cold hardiness of honey bee, Apis mellifera L.

Like many insects, honey bee can increase its cold tolerance through freeze avoidance, using antifreeze proteins (AFPs) to lower its supercooling point (SCP). Proline is the most dominant amino acid in honey bee hemolymph, which can be obtained by the insect through feeding. In the current study the antifreeze activity of this amino acid was evaluated on worker honey bees, immediately before the start of cold season. The experiment was established on four treatments including three different concentrations of proline (1%, 3% and 4.35%) diluted in 1:1 water sucrose syrup, and the syrup without proline (control). Newly emerged worker honey bees were fed on the mentioned diets for 2 weeks, under cage condition, and then 20 bees from each treatment (cage) were selected randomly for determination of cold hardiness inside a cooling bath. Using a CHY data logger, equipped with a K100 sensor attached to the bee’s gaster, the SCP, the amount of released heat and the rate of this release as measures of insect cold hardiness were recorded. Proline significantly reduced honey bees’ SCP. The lowest point, -7.67±0.2646°C, was observed in the concentration of 1% proline. The amount of released heat and the rate of this release were not significantly different across the treatments.

Roles of Aquaporins in Osmoregulation, Desiccation and Cold Hardiness in Insects

To maintain water homeostasis and osmoregulation, and to facilitate cryoprotection or overcome desiccation challenges, organisms across all taxa have utilized special and elaborate transmembrane channels that mediate the transport of water molecules (aquaporins, AQPs) as well as uncharged low molecular-weight solutes, such as glycerol (aquaglyceroporins). Nevertheless, some channels like Big Brain (BIB) in Drosophila play different roles that are involved in neural signal transduction, cell migration and cell to cell adhesion. Sanguinivorous insects and ticks, or insects feeding on plant sap are challenged with large volumes of ingested solutes that must be rapidly and effectively voided. AQP genes encoding functional transmembrane channel proteins were cloned from various ticks and mosquitoes species, as well as from xylem- (green leafhoppers) and phloem-sap feeders (whiteflies and aphids). AQPs are largely and abundantly expressed in organs associated with water balance such as the Malpighian tubules and the alimentary canal. In particular, abundance of AQP channels were detected in gut bypasses like the filter chamber in plant-sap feeders. AQPs and mobilization of cryoprotectants or dehydration protectants like glycerol and other polyols were studied in insects that overcome extreme environmental conditions such as sub-zero temperatures or severe desiccation. Hormone-mediated transcriptional regulation of AQP genes was demonstrated in insect and vertebrate systems. Post-translational control, related to trafficking of AQP-containing intracellular membrane vesicles to appropriate location in cell membrane domains, their docking on and fusion with the plasma membrane compartment, recycling and degradation as well as gating their pore entrance, was largely associated with specific kinase-mediated phosphorylation steps. Most of the above research was conducted with mammalian systems, yet several solid lines of evidence show that the same mechanisms apply to insects. As AQPs are tightly linked to human pathophysiological conditions, they have become promising targets for developing pharmaceutical drugs. Likewise, since AQPs are important for the survival of blood and plant-sap feeding arthropods, they have been suggested as attractive target sites to be tapped for developing effective pest control agents.

Insect cold hardiness: metabolic, gene, and protein adaptation1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era.

Winter survival for thousands of species of insects relies on adaptive strategies for cold hardiness. Two basic mechanisms are widely used (freeze avoidance by deep supercooling and freeze tolerance where insects endure ice formation in extracellular fluid spaces), whereas additional strategies (cryoprotective dehydration, vitrification) are also used by some polar species in extreme environments. This review assesses recent research on the biochemical adaptations that support insect cold hardiness. We examine new information about the regulation of cryoprotectant biosynthesis, mechanisms of metabolic rate depression, role of aquaporins in water and glycerol movement, and cell preservation strategies (chaperones, antioxidant defenses and metal binding proteins, mitochondrial suppression) for survival over the winter. We also review the new information coming from the use of genomic and proteomic screening methods that are greatly widening the scope for discovery of genes and proteins that support winter survival.

Advances in insect physiology and endocrinology through genomics, peptidomics, and related technologies1Introduction to the virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era.

This series of the Canadian Journal of Zoology brings together scientists actively working on insect physiology and endocrinology in this postgenomic era. This issue is timely and appropriate. Timely, because of the pace of change brought about by genome projects, functional genomics and genetics (omics technologies), including gene microarrays, mutations, RNAi, and sophisticated mass spectrometry techniques, which are helping to unravel complex regulatory processes. Appropriate, because Canada, and the Canadian Journal of Zoology, has a rich history and strong tradition of cutting-edge research in insect biology—with particular strengths in insect physiology and endocrinology. The first review illustrates how these very modern omics technologies can be embraced and applied to insect physiology and endocrinology, and the subsequent reviews illustrate this in practice, with regard to insect cold hardiness, insulin signaling and stress, peptidergic control of food intake and digestion, endocrine control of diuresis, and finally allatoregulatory peptides. These reviews set the scene and context for the exciting era that we find ourselves in, and the depth of understanding that has come from this postgenomic revolution.

Cold Hardiness of Helicoverpa zea (Lepidoptera: Noctuidae) Pupae

An insect's cold hardiness affects its potential to overwinter and outbreak in different geographic regions. In this study, we characterized the response of Helicoverpa zea (Boddie) pupae to low temperatures by using controlled laboratory measurements of supercooling point (SCP), lower lethal temperature (LT(50)), and lower lethal time (LLTime). The impact of diapause, acclimation, and sex on the cold hardiness of the pupae also were evaluated. Sex did not significantly affect the SCP, LT(50), or LLTime. However, the mean SCP of diapausing pupae (-19.3°C) was significantly lower than nondiapausing pupae (-16.4°C). Acclimation of nondiapausing pupae to constant temperatures from 10 to 20°C before supercooling also produced a significantly lower SCP than nondiapausing pupae held at 25°C. The LT(50)s of nondiapausing and diapausing were not significantly different, but confirmed that H. zea pupae are chill-intolerant because these lethal temperatures are warmer than the corresponding mean SCPs. Diapausing pupae survived longer than nondiapausing pupae at the same, constant, cold temperatures, a finding consistent with the SCP results. Both of these results suggest enhanced cold hardiness in diapausing pupae. When laboratory results were compared with field temperatures and observed distributions of H. zea in the contiguous United States, the laboratory results corroborated what is currently perceived to be the northern overwintering limit of H. zea; approximately the 40(th) parallel. Moreover, our research showed that areas north of this limit are lethal to overwintering pupae not because of low temperature extremes, but rather the length of time spent at near-zero temperatures.

Genomics, proteomics and metabolomics: Finding the other players in insect cold tolerance

Introduction Our understanding of the physiological mechanisms of insect cold-hardiness relies on a rich history of discovery that has revealed the presence of cryoprotective agents, antifreeze proteins, ice-nucleating proteins, heat-shock proteins and modifications of the cell membrane. Such discoveries have usually targeted select metabolites, proteins, or fatty acids, and have successfully revealed the identity of many key agents that protect insects from injury at low temperature, yet we suspect that, in many cases, additional protective agents may be involved. In some cases this may mean the potential discovery of entirely new cryoprotective agents or discovery of roles for a multitude of chemical modifications that may accompany a change in a single compound that has already been well documented. This is indeed the power of the “-omics” approach, discovery of large-scale changes at levels of the transcript (genomics or transcriptomics), protein (proteomics), or metabolites (metabolomics). These approaches are especially good for seeing the big picture. What novel genes or gene pathways are turned on or off? What proteins are uniquely synthesized or post-translationally modified in respond to the cold? What is the full range of metabolic change that occurs in response to cold, and what metabolic pathways are affected? These are the sorts of questions that can be uniquely answered by genomics, proteomics and metabolomics. Clearly, all of these approaches mark, not the end of the discovery phase, but the beginning.

Freezing tolerance and low molecular weight cryoprotectants in an invasive parasitic fly, the deer ked (Lipoptena cervi)

Insect cold hardiness is often mediated by low molecular weight cryoprotectants, such as sugars, polyols, and amino acids (AA). While many free-living northern insects must cope with extended periods of freezing ambient temperatures (Ta), the ectoparasitic deer ked Lipoptena cervi imago can encounter subfreezing Ta only during a short autumnal period between hatching and host location. Subsequently, it benefits from the body temperature of the cervid host for survival in winter. This study investigated the cold tolerance of the species by determining its lower lethal temperature (100% mortality, LLT100) during faster and slower cold acclimation, by determining the supercooling point (SCP) and by measuring the concentrations of potential low molecular weight cryoprotectants. The LLT100 of the deer ked was approximately -16 ° C, which would enable it to survive freezing nighttime Ta not only in its current area of distribution but also further north. The SCP was -7.8 ° C, clearly higher than the LLT100 , indicating that the deer ked displays freezing tolerance. The concentrations of free AA, especially nonessential AA, were higher in the cold-acclimated deer keds similar to several other insects. The concentrations of proline increased together with γ-aminobutyrate, arginine, asparagine, cystine, glutamate, glutamine, hydroxylysine, sarcosine, serine, and taurine. AA could be hypothesized to act as cryoprotectants by, e.g., protecting enzymes and lipid membranes from damage caused by cold.

In Cold‐Hardy Insects, Seasonal, Temperature, and Reversible Phosphorylation Controls Regulate Sarco/Endoplasmic Reticulum Ca2+‐ATPase (SERCA)

Winter cold hardiness of insects typically involves one of two major strategies for survival below 0 degrees C: freeze avoidance and freeze tolerance. The two strategies have some common features, including the accumulation of high concentrations of cryoprotectant polyols and the frequent occurrence of diapause. Entry into the hypometabolic state of diapause requires coordinated suppression of major ATP-consuming metabolic processes, and ion motive ATPases are important targets for regulation. This study documents the suppression of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) activity in the overwintering larvae of two cold-hardy species, the freeze-avoiding gall moth Epiblema scudderiana and the freeze-tolerant gall fly Eurosta solidaginis. Activity was reduced despite a lack of change in SERCA protein levels in E. solidaginis larvae over the winter and a six- to eightfold increase in SERCA protein in E. scudderiana. This implicated posttranslational modification as the mechanism of SERCA suppression, and in vitro incubations indicated that enzyme phosphorylation by protein kinases A, G, or C strongly reduced enzyme activity. A stable reduction in SERCA activity was also seen in cold-acclimated larvae of both species compared with 15 degrees C controls, with significant changes in the kinetic parameters of the E. scudderiana enzyme (e.g., K(m) ATP was 3.2-fold higher in -20 degrees C-acclimated larvae) that were consistent with reduced enzyme function at low temperature. Epiblema scudderiana SERCA was also subject to regulation by differential temperature effects (Arrhenius activation energy increased by approximately threefold below 10 degrees C) and by seasonal changes in the levels of a SERCA inhibitor protein, phospholamban.

Impact of Host Tree on Forest Tent Caterpillar Performance and Offspring Overwintering Mortality

One of the most damaging insect pests in deciduous forests of North America is the forest tent caterpillar, Malacosoma disstria Hübner. It can feed on a variety of plants, but trembling aspen (Populus tremuloides Michaux) is its preferred host and sugar maple (Acer saccharum Marshall) serves as a secondary one in the northern part of its distribution. Because host plant characteristics influence insect performance and survival, we evaluated the impact of trembling aspen and sugar maple foliage on M. disstria performance. Host effects on insect cold hardiness and overwintering survival of offspring were also studied. Forest tent caterpillar reared on aspen leaves had a shorter development time, higher pupal weights and fecundity, and superior egg parameters (length and weight) compared with those reared on sugar maple leaves. Larvae from the two food treatments had low glucose levels during diapause, whereas glycerol content of insects reared on maple was significantly higher during diapause than larvae fed on aspen. Lower glycerol content may explain the higher overwinter mortality of pharate larvae from aspen-reared parents even though their supercooling points were as low as -36 degrees C. This study shows the influence of host plant on insect life history and the need to consider overwintering success and offspring performance in studies to understand and predict population growth and cycling.

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 °C min −1) and slow (0.03 °C min −1) rates of temperature reduction down to −10 °C. No adults survived cooling to −10 °C at either cooling rate. Mean supercooling points (SCPs) from fast cooling were −7.0 and −4.6 °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 °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 °C, indicating their longevity at more favourable temperatures. Members of the Apteropanorpidae are adapted to the relatively warm, maritime climate currently influencing Tasmania.