Fluctuating Thermal Regime Research Articles

Assessing the effects of cold storage regimes of North American Bombus Gynes

AbstractBumble bees are the primary commercial pollinators for greenhouse‐grown crops and managing them requires insight into the Bombus life cycle. However, some aspects of the life cycle are not fully understood. Once mated, adult Bombus gynes can be stored for a short term at a constant low temperature (CLT). However, survival rates for some species are low during CLT, particularly when storage periods exceed a month. To address this, we tested the hypothesis that Bombus gynes stored in a fluctuating thermal regime (FTR) have increased survival compared to gynes stored in CLT. Specifically, the FTR had a baseline temperature of 2°C, with a daily fluctuation to 20°C relative to the CLT of 2°C with no warming pulse. We tested the effects of FTR on gyne survival and post‐cold storage lipid content in three species used for commercial pollination in North America: B. vosnesenskii, B. huntii and B. impatiens. We further assessed how additional factors influence cold storage survival, including gyne body weight, body size and colony age. Survival responses varied among species. Bombus vosnesenskii and B. huntii had a lower survival rate in FTR compared to CLT, but B. impatiens gynes had a significantly higher survival rate in FTR. We did not observe significant effects of FTR on lipid stores for any species, but survival increased with an increasing initial weight prior to cold storage. Moreover, gynes produced later in the colony life cycle had lower body weight and decreased survival compared to early emerging gynes. Our study provides insight into how cold storage conditions interact with colony and gyne characteristics to influence captive overwintering survival. Our findings have economic applications for improving commercial rearing and efforts for conservation rearing of at‐risk Bombus species.

Effects of Temperature and Wildflower Strips on Survival and Macronutrient Stores of the Alfalfa Leafcutting Bee (Hymenoptera: Megachilidae) Under Extended Cold Storage.

Megachile rotundata (F.) is an important pollinator of alfalfa in the United States. Enhancing landscapes with wildflowers is a primary strategy for conserving pollinators and may improve the sustainability of M. rotundata. Changing cold storage temperatures from a traditionally static thermal regime (STR) to a fluctuating thermal regime (FTR) improves overwintering success and extends M. rotundata’s shelf life and pollination window. Whether floral resources enhance overwintering survival and/or interact with a thermal regime are unknown. We tested the combined effects of enhancing alfalfa fields with wildflowers and thermal regime on survival and macronutrient stores under extended cold storage (i.e., beyond one season). Megachile rotundata adults were released in alfalfa plots with and without wildflower strips. Completed nests were harvested in September and stored in STR. After a year, cells were randomly assigned to remain in STR for 6 months or in FTR for a year of extended cold storage; emergence rates were observed monthly. Macronutrient levels of emerged females were assessed. FTR improved M. rotundata survival but there was no measurable effect of wildflower strips on overwintering success or nutrient stores. Timing of nest establishment emerged as a key factor: offspring produced late in the season had lower winter survival and dry body mass. Sugars and glycogen stores increased under FTR but not STR. Trehalose levels were similar across treatments. Total lipid stores depleted faster under FTR. While wildflowers did not improve M. rotundata survival, our findings provide mechanistic insight into benefits and potential costs of FTR for this important pollinator.

Consequences of Thermal Variation during Development and Transport on Flight and Low-Temperature Performance in False Codling Moth (Thaumatotibia leucotreta): Fine-Tuning Protocols for Improved Field Performance in a Sterile Insect Programme

Simple SummaryIn two separate experiments, we examined how (1) developmental temperature and (2) transport conditions influenced the low-temperature performance and flight ability of false codling moth (FCM) adults. In experiment 1, larvae were exposed to a control (constant 25 °C), a cold treatment (constant 15 °C) or a fluctuating thermal regime (FTR) (25 °C for 12 h; 15 °C for 12 h) for 5 days, whereafter larvae were returned to 25 °C to pupate and emerge. After adult emergence, cold tolerance, life history traits and flight ability were scored. In experiment 2, adult FCM were exposed to 4 or 25 °C, with or without vibrations, whereupon flight ability, spontaneous behaviour (i.e., muscle coordination by monitoring whether the moth moved out of a defined circle or not) and cold tolerance were determined. The results of the first experiment showed that FTR led to enhanced cold tolerance, increased flight performance and high egg-laying capacity with minimal costs. The results of the second experiment showed that transport conditions currently in use did not appear to adversely affect flight and cold performance of FCM. These results are significant for refining conditions prior to and during release for maximum field efficacy in an SIT programme.Here we aimed to assess whether variation in (1) developmental temperature and (2) transport conditions influenced the low-temperature performance and flight ability of false codling moth (FCM) adults in an SIT programme. To achieve the first aim, larvae were exposed to either a (control) (constant 25 °C), a cold treatment (constant 15 °C) or a fluctuating thermal regime (FTR) (25 °C for 12 h to 15 °C for 12 h) for 5 days, whereafter larvae were returned to 25 °C to pupate and emerge. After adult emergence, critical thermal minimum, chill coma recovery time, life history traits and laboratory flight ability were scored. For the second aim, adult FCM were exposed to 4 or 25 °C with or without vibrations to simulate road transportation. After the pre-treatments, flight ability, spontaneous behaviour (i.e., muscle coordination by monitoring whether the moth moved out of a defined circle or not) and chill coma recovery time were determined. The first experiment showed that FTR led to enhanced cold tolerance, increased flight performance and high egg-laying capacity with minimal costs. The second experiment showed that transport conditions currently in use did not appear to adversely affect flight and low-temperature performance of FCM. These results are important for refining conditions prior to and during release for maximum field efficacy in an SIT programme for FCM.

Comparison of Fluctuating Thermal Regimes and Commercially Achievable Constant-Temperature Regimes for Short-Term Storage of the Alfalfa Leafcutting Bee (Hymenoptera: Megachilidae).

Interrupting the spring incubation of Megachile rotundata (F.) with a period of low-temperature storage for synchronizing the bees' emergence with crop bloom is an essential part of M. rotundata management. Previously, we demonstrated that bees exposed to thermoperiods (TPs) during low-temperature storage have higher survival rates than bees exposed to constant temperatures. But changing the temperature in the large mass of bees commonly found in most commercial settings would place considerable stress on the chambers' refrigeration system. Reducing the difference between a TP's cryophase and thermophase would decrease the stress on the refrigeration system. Therefore, we investigated a range of TPs with cryophases (12 h) of 6, 12, or 15°C and thermophases (12 h) of 15 or 18°C and compared the survival rates of these bees against bees exposed to constant temperatures of 12, 15, or 18°C. For eye-pigmented pupae, the TP 6-18°C and the control fluctuating thermal regime (FTR; 6°C with a daily 1-h pulse at 20°C) had the highest survival rates for the 2 yr tested. For the constant-temperature storage protocols, constant 15 and 18°C were either equivalent or lower survival than the control FTR. For emergence-ready adults, the 6-18°C TP had the highest survival rates. The constant 15°C and the control FTR had equivalent survival rates. Under the current constraints imposed by a commercial chamber's refrigeration system, interrupting M. rotundata spring incubation by exposing the developing bees to constant temperatures of 15-18°C is currently the best option for commercial operations.

Fluctuating thermal regimes prevent chill injury but do not change patterns of oxidative stress in the alfalfa leafcutting bee, Megachile rotundata

In insects, prolonged exposure to unseasonably low temperatures can lead to detrimental physiological effects known as chill injury. Changes to active and passive transport across epithelia during chilling likely drive the collapse of ion gradients, metabolic imbalance and potentially oxidative stress. In the alfalfa leafcutting bee, Megachile rotundata transcriptomic evidence provides support for these responses at the level of gene expression, but variable expression profiles between life stages in M. rotundata indicate that different mechanisms could be responsible for repairing and protecting against chill injuries across development. Herein, we test the hypotheses that 1) chill injury leads to oxidative stress and damage in insects and 2) exposure to a fluctuating thermal regime (FTR) promotes an increased oxidative stress response leading to a decrease in damage by reactive oxygen species. We measured the expression of transcripts with products known to have antioxidant properties in overwintering prepupae as well as total antioxidant capacity and lipid peroxidation during both extended overwintering in prepupae and low temperature stress during pupal development. We observed differential gene expression for the antioxidant glutathione peroxidase and several transcripts with putative antioxidant properties including vitellogenin, apolipoprotein D, glutathione S-transferase, and nuclear protein 1. However, the expression of transcripts coding for other enzymatic antioxidants did not change between treatments. Neither life stage varied in their capacity to cope with an induced oxidative stress after FTR exposure and we did not observe evidence of lipid peroxidation in chill injured (STR) prepupae. These results did not support our initial hypotheses and indicate that oxidative-stress-induced damage is neither a causal factor or symptom of chill injury.

Thermoprofile Parameters Affect Survival of Megachile rotundata During Exposure to Low-Temperatures.

Insects exposed to low temperature stress can experience chill injury, but incorporating fluctuating thermoprofiles increases survival and blocks the development of sub-lethal effects. The specific parameters required for a protective thermoprofile are poorly understood, because most studies test a limited range of thermoprofiles. For example, thermoprofiles with a wave profile may perform better than a square profile, but these two profiles are rarely compared. In this study, two developmental stages of the alfalfa leafcutting bee, Megachile rotundata, eye-pigmented pupae, and emergence-ready adults, were exposed to one of eight thermoprofiles for up to 8 weeks. All the thermoprofiles had a base of 6°C and a peak temperature of either 12°C or 18°C. The duration at peak temperature varied depending on the shape of the thermoprofile, either square or wave form. Two other treatments acted as controls, a constant 6°C and a fluctuating thermal regime (FTR) with a base temperature of 6°C that was interrupted daily by a single, 1-h pulse at 20°C. Compared with constant 6°C, all the test thermoprofiles significantly improved survival. Compared with the FTR control, the thermoprofiles with a peak temperature of 18°C outperformed the 12°C profiles. Bees in the eye-pigmented stage exposed to the 18°C profiles separated into two groups based on the shape of the profile, with higher survival in the square profiles compared with the wave profiles. Bees in the emergence-ready stage exposed to 18°C profiles all had significantly higher survival than bees in the FTR controls. Counter to expectations, the least ecologically relevant thermoprofiles (square) had the highest survival rates and blocked the development of sub-lethal effects (delayed emergence).

Immediate Transcriptional Response to a Temperature Pulse under a Fluctuating Thermal Regime.

The response of ectotherms to temperature stress is complex, non-linear, and is influenced by life stage and previous thermal exposure. Mortality is higher under constant low temperatures than under a fluctuating thermal regime (FTR) that maintains the same low temperature but adds a brief, daily pulse of increased temperature. Long term exposure to FTR has been shown to increase transcription of genes involved in oxidative stress, immune function, and metabolic pathways, which may aid in recovery from chill injury and oxidative damage. Previous research suggests the transcriptional response that protects against sub-lethal damage occurs rapidly under exposure to fluctuating temperatures. However, existing studies have only examined gene expression after a week or over many months. Here we characterize gene expression during a single temperature cycle under FTR. Development of pupating alfalfa leafcutting bees (Megachile rotundata) was interrupted at the red-eye stage and were transferred to 6°C with a 1-h pulse to 20°C and returned to 6°C. RNA was collected before, during, and after the temperature pulse and compared to pupae maintained at a static 6°C. The warm pulse is sufficient to cause expression of transcripts that repair cell membrane damage, modify membrane composition, produce antifreeze proteins, restore ion homeostasis, and respond to oxidative stress. This pattern of expression indicates that even brief exposure to warm temperatures has significant protective effects on insects exposed to stressful cold temperatures that persist beyond the warm pulse. Megachile rotundata’s sensitivity to temperature fluctuations indicates that short exposures to temperature changes affect development and physiology. Genes associated with developmental patterning are expressed after the warm pulse, suggesting that 1 h at 20°C was enough to resume development in the pupae. The greatest difference in gene expression occurred between pupae collected after the warm pulse and at constant low temperatures. Although both were collected at the same time and temperature, the transcriptional response to one FTR cycle included multiple transcripts previously identified under long-term FTR exposure associated with recovery from chill injury, indicating that the effects of FTR occur rapidly and are persistent.

Fluctuating thermal regime preserves physiological homeostasis and reproductive capacity in Drosophila suzukii

Drosophila suzukii, an invasive species recently introduced in Europe, lays eggs in thin-skinned fruits and causes huge financial losses to fruit growers. One potential way to control this pest is the sterile insect technique (SIT) which demands a large stock of reproductive females to produce millions of sterile males to be released on demand. Unfortunately, Drosophila stocks age quickly, show declining fecundity when maintained at warm temperatures and conversely, they die from chill injury if they are maintained at constant low temperature. Here we investigate the potential of fluctuating thermal regime (FTR) as a storage method that harness the benefits of both warm and cold storage. Using a FTR with a daily warm period (1 h 20 at 25 °C) and cold period (20 h at 3 °C), interspaced by gradual heating and cooling, we compared longevity, fecundity and physiological condition between FTR females and females exposed to constant 25 °C and 3 °C. As hypothesised, FTR flies experienced much slower senescence (>3-fold increase in lifespan) and they preserved fecundity to a much higher age than flies from constant 25 °C. Flies maintained at constant 3 °C quickly died from chill injuries caused by a gradual loss of ion and water balance. In contrast, FTR flies were able to maintain ion and water balance (similar to 25 °C flies) as they were allowed to recover homeostasis during the short warm periods. Together these results demonstrate that FTR represents a useful protocol for storage of Drosophila stocks, and more broadly, this shows that the benefits of FTR are tightly linked with the insect ability to recover physiological homeostasis during the short warm periods.

Physiological responses to fluctuating temperatures are characterized by distinct transcriptional profiles in a solitary bee.

Exposure to stressful low temperatures during development can result in the accumulation of deleterious physiological effects called chill injury. Metabolic imbalances, disruptions in ion homeostasis and oxidative stress contribute to the increased mortality of chill-injured insects. Interestingly, survival can be significantly increased when chill-susceptible insects are exposed to a daily warm-temperature pulse during chilling. We hypothesize that warm pulses allow for the repair of damage associated with chill injury. Here, we describe transcriptional responses during exposure to a fluctuating thermal regime, relative to constant chilled temperatures, during pupal development in the alfalfa leafcutting bee, Megachile rotundata, using a combination of RNA-seq and qPCR. Pupae were exposed to either a constant, chilled temperature of 6°C, or 6°C with a daily pulse of 20°C for 7days. RNA-seq after experimental treatment revealed differential expression of transcripts involved in construction of cell membranes, oxidation-reduction and various metabolic processes. These mechanisms provide support for shared physiological responses to chill injury across taxa. The large number of differentially expressed transcripts observed after 7days of treatment suggests that the initial divergence in expression profiles between the two treatments occurred upstream of the time point sampled. Additionally, the differential expression profiles observed in this study show little overlap with those differentially expressed during temperature stress in the diapause state of M. rotundata While the mechanisms governing the physiological response to low-temperature stress are shared, the specific transcripts associated with the response differ between life stages.

Physiological basis for low-temperature survival and storage of quiescent larvae of the fruit fly Drosophila melanogaster.

The cryopreservation techniques proposed for embryos of the fruit fly Drosophila melanogaster are not yet ready for practical use. Alternative methods for long-term storage of D. melanogaster strains, although urgently needed, do not exist. Herein, we describe a narrow interval of low temperatures under which the larvae of D. melanogaster can be stored in quiescence for up to two months. The development of larvae was arrested at the pre-wandering stage under fluctuating thermal regime (FTR), which simultaneously resulted in diminishing the accumulation of indirect chill injuries. Our physiological, metabolomic, and transcriptomic analyses revealed that compared to larvae stored at constant low temperatures, the larvae stored under FTR conditions were able to decrease the rates of depletion of energy substrates, exploited brief warm episodes of FTR for homeostatic control of metabolite levels, and more efficiently exerted protection against oxidative damage.

Fluctuating versus constant temperatures: effects on metabolic rate and oxidative damages in freshwater crustacean embryos

Rising temperatures will pose a major threat, notably for freshwater ecosystems, in the decades to come. Temperature, a major environmental factor, affects organisms’ physiology and metabolism. Most studies of temperature effect address constant thermal regime (CTR), whereas organisms are exposed to fluctuating thermal regime (FTR) in their natural environments. In addition, previous works have predominantly addressed issues of thermal tolerance in adults rather than in early life stages. Therefore, for the first time to our knowledge, we aimed to investigate the influence of thermal conditions, either FTR or CTR, on the physiology of the crustacean amphipod Gammarus roeseli Gervais, 1835 at different embryonic stages. We measured the metabolic rate and the TBARS (thiobarbituric acid reactive substances) body content (to assess the level of oxidative damage). Oxygen consumption rate strongly increased throughout embryo development, whereas oxidative damages did not clearly change. In addition, the embryos tended to consume oxygen equally but displayed less oxidative damage when developing under FTR compared with developing under CTR. Moreover, our results revealed that fluctuating temperatures (and especially the existence of a colder (nonstressful) period during the day) could allow cell-damage repairs, and therefore, allow G. roeseli embryos to ensure good development by implementing an efficient protection response against oxidative stress.

Optimizing Fluctuating Thermal Regime Storage of Developing Megachile rotundata (Hymenoptera: Megachilidae).

The alfalfa leafcutting bee, Megachile rotundata (F.), is the primary pollinator for alfalfa seed production in North America. Under current management practice, developing pupae are incubated at 29-30°C until the adults emerge for pollination. If unfavorable spring weather delays peak alfalfa bloom, managers will cool pupae to slow development, which can increase mortality and causes sublethal effects. Previously, we demonstrated that exposure to a fluctuating thermal regime (FTR) increases survival and extends the viable storage period. To determine the optimal conditions for FTR during storage of developing M. rotundata , we examined four variables: temperature of the daily warm pulse, duration of the warm pulse, number of weeks exposed to the FTR treatment, and developmental stage of the bee. Survival was measured by successful eclosion to the adult stage. Under all conditions, exposure to FTR increased survival compared with exposure to a constant 6°C. When the temperature of the daily warm pulse was 20-25°C from a base temperature of 6°C, and the pulse duration was extended to 3 h, survival rates were as high as those observed under standard storage conditions (29°C). Under this FTR storage protocol, bee managers can delay emergence for ∼8 wk without significant decreases in survival. Our findings have substantial economic implications for bee management and alfalfa seed production by increasing the flexibility and efficiency of M. rotundata adult emergence.

A Fluctuating Thermal Regime Improves Long-Term Survival of Quiescent Prepupal <I>Megachile rotundata</I> (Hymenoptera: Megachilidae)

The alfalfa leafcutting bee Megachile rotundata (F.) is the primary pollinator for alfalfa seed production. Under standard management conditions, the alfalfa leafcutting bee develops to the diapausing prepupal stage under field conditions, after which they are cold-stored at a static temperature until the following spring, when temperatures are raised and development resumes. We have assessed the effects of a fluctuating thermal regime (FTR) during overwintering cold storage, where bees were exposed to a daily 1 h pulse of 20 degrees C, and compared viability and insect quality to bees stored under a static thermal regime. Our results demonstrate that implementing an FTR protocol dramatically increases the survival of cold-stored alfalfa leafcutting bees, effectively extending their shelf-life into the subsequent growing season. These findings could substantially ameliorate significant obstacles that restrict the more widespread use of this important pollinator, such as the biological constraints that restrict its use in early blooming crops, and yearly fluctuations in bee prices that add significant financial uncertainty to end users. This study also strengthens a growing body of evidence that indicates FTR protocols are superior to static thermal regime protocols for insect cold storage.

Duration and Frequency of a High Temperature Pulse Affect Survival of Emergence-Ready Megachile rotundata (Hymenoptera: Megachilidae) During Low-Temperature Incubation

Synchronizing Megachile rotundata (F.) nesting activity with alfalfa bloom is essential for ensuring optimal pollination for alfalfa seed production. This is achieved by timing the initiation of spring bee incubation so that adults will emerge -2 wk before peak bloom. If weather conditions change so as to delay the bloom, bee managers will commonly expose the developing bees to a period of low-temperature incubation to slow their development. We have previously demonstrated survival during low-temperature incubation can be significantly increased by using a fluctuating thermal regime (FTR) where the bees receive a daily pulse at 20 degrees C. A FTR incubation protocol is composed of a number of different components, such as the base and pulse temperatures, and the duration and frequency of the pulse. In this investigation, the effect of the duration of the pulse (5-120 min) and the frequency of a pulse (twice daily to weekly) on the survival of developing M. rotundata was examined. A pulse as short as 5 min at 20 degrees C increased survival of the developing bees as compared with the constant 6 degrees C controls. Increasing the pulse duration induced a further increase in tolerance to 6 degrees C. As with the pulse duration, increasing the pulse frequency from once weekly to twice daily had a significant effect on improving the bees tolerance to low-temperature incubation. This investigation further strengthens the argument that a FTR protocol is superior to using a constant low-temperature exposure for interrupting the spring incubation of M. rotundata.

Cyclic CO2 emissions during the high temperature pulse of fluctuating thermal regime in eye-pigmented pupae of Megachile rotundata

Megachile rotundata (Hymenoptera: Megachilidae), the primary pollinator used in alfalfa seed production, may need to be exposed to low-temperature storage to slow the insects' development to better match spring emergence with the alfalfa bloom. It has been demonstrated that using a fluctuating thermal regime (FTR) improves the tolerance of pupae to low temperatures. Carbon dioxide emission rates were compared between four different FTRs, all with a base temperature of 6°C and a daily high-temperature pulse. Four different high-temperature pulses were examined, 15 or 25°C for 2h and 20°C for 1 or 2h. A subset of pupae at the FTR base temperature of 6°C exhibited continuous gas exchange and, once ramped to 20 or 25°C, shifted to cyclic gas exchange. As temperatures were ramped down from the high-temperature pulse to 6°C, the pupae reverted to continuous gas exchange. The following conclusions about the effect of FTR on the CO2 emissions of M. rotundata pupae exposed to low-temperature storage during the spring incubation were reached: 1) the high temperature component of the FTR was the best predictor of respiratory pattern; 2) neither pupal body mass nor days in FTR significantly affected which respiratory pattern was expressed during FTRs; 3) cyclic gas exchange was induced only in pupae exposed to temperatures greater than 15°C during the FTR high temperature pulse; and 4) a two hour pulse at 25°C doubled the number of CO2 peaks observed during the FTR pulse as compared to a two hour pulse at 20°C.

A Fluctuating Thermal Regime Improves Survival of Cold-Mediated Delayed Emergence in Developing Megachile rotundata (Hymenoptera: Megachilidae)

A significant concern in the commercial application of the alfalfa leafcutting bee, Megachile rotundata (F.) (Hymenoptera: Megachilidae), for pollination is synchronizing bee emergence and activity with peak crop bloom. Previous studies have demonstrated that the commercial spring incubation of this species can be successfully interrupted by low temperature incubation, thereby slowing development and giving producers flexibility in timing emergence to weather conditions or crop bloom. In this study, we demonstrate that the implementation of a fluctuating thermal regime, during which bees are given a daily one hour pulse of high temperature, markedly increases the "shelf-life" of individuals of this species. Although constant temperatures can be used to store bees for up to 1 wk with no decrease in survival, properly staged bees can be stored for up to 6 wk without a significant decrease in percentage of emergence. Hence, we expect fluctuating thermal regime protocols to become a valuable tool for M. rotundata managers, especially when timing nesting activity with peak bloom to maximize effectiveness.

A model for the time–temperature–mortality relationship in the chill-susceptible beetle, Alphitobius diaperinus, exposed to fluctuating thermal regimes

Exposing insects to a fluctuating thermal regime (FTR) compared with constant low temperature (CLT) significantly reduces cold-induced mortality. The beneficial effects of FTR result from physiological repair during warming intervals. The duration and the temperature experienced during the recovery period are supposed to strongly impact the resulting cold survival; however, disentangling the effects of both recovery variables had not been broadly investigated. In this study, we investigate cold tolerance (lethal time, Lt 50) of the polyphagous beetle Alphitobius diaperinus. We examined adult survival under various CLTs (0, 5, 10 and 15 °C), and under 20 different FTR conditions, where the 0 °C exposure alternated with various recovery temperatures (Rt) (5, 10, 15 and 20 °C) combined with various recovery durations (Rds) (0.5, 1, 2, 3 and 4 h). Under CLTs, Lt 50 increased with temperature until no mortality occurred above the upper limit of cold injury zone (ULCIZ). Under FTRs, Lt 50 increased with both Rt and Rd. The magnitude of the survival gain was clearly boosted when Rt was above the ULCIZ (at 20 °C). Based on a data matrix of lethal times with multiple Rt×Rd combinations, a predictive model showed that cold survival increased exponentially with Rt and Rd. This model was subsequently validated with additional survival tests. We suggest that increasing recovery durations associated with optimal recovery temperatures eventually leads to a progressive chilling compensation.

Does fluctuating thermal regime trigger free amino acid production in the parasitic wasp Aphidius colemani (Hymenoptera: Aphidiinae)?

When stressful cold-exposure is interrupted by short warm intervals, physiological recovery is possible, and this improves markedly the survival of insects. Fluctuating thermal regime (FTR) may act as a cue triggering the initiation of a metabolic response involving synthesis of cryoprotective compounds, such as free amino acids (FAA). Since specific changes in FAA levels can provide a good indication of the overall response of an organism to stressful conditions, we investigated temporal changes in FAA body contents of the parasitoid Aphidius colemani Viereck during exposure to FTR (4 degrees C: 20 degrees C for 22 h: 2 h per day) versus constant low temperature (4 degrees C). Physiological response during cold-exposure was clearly dissimilar between thermal treatments. Under constant cold-exposure FAA pool increased, whereas it decreased with cold-exposure duration in FTR. No single FAA accumulation could explain the higher survival under FTR. We propose that instead of considering FAA as a part of cryoprotective arsenal, FAA accumulation should rather be regarded as a symptom of a cold-induced physiological response. This is much less manifest under FTR, as the warm intervals likely allow a periodic reactivation of normal metabolic activities and a recovery of developmental processes.

Temperature Compensation of [ U - 14 C]Glucose Incorporation by Microbial Communities in a River with a Fluctuating Thermal Regime

In summer, the river Saar in the southwest of Germany exhibits distinct temperature fluctuations from 8 degrees C at the source to nearly 30 degrees C in the middle region. Temperature optima for bacterial plate counts and the uptake velocity of [U-C]glucose by the natural microbial communities of different regions ranged from 20 to 30 degrees C, which is significantly above the mean annual water temperature. A correlation between temperature optima and different seasons or habitats was not observed. Despite the relatively high temperature optima, the turnover time for glucose was shortest at temperatures around the mean annual water temperature, due to changes in the substrate affinity. At limiting substrate concentrations, the higher substrate affinity at lower temperatures may lead to a higher real activity at in situ temperatures, and a compensatory stabilization of uptake rates at fluctuating temperatures is possible.