Thermal effect of blood feeding in the telmophagous fly Glossina morsitans morsitans

During feeding on warm-blooded hosts, haematophagous insects are exposed to thermal stress due to the ingestion of a meal which temperature may highly exceed their own body temperature. In order to avoid overheating and its subsequent deleterious effects, these insects respond by setting up molecular protective mechanisms such as heat shock proteins synthesis or by using thermoregulative strategies. Moreover, the duration of contact with the host depends on the way of feeding displayed by the different species (either telmophagous or solenophagous) and thus also impacts their exposure to heat. Solenophagous insects feed directly on blood vessels and are relatively slow feeders while telmophagous insects by lacerating capillaries, facilitate their access to blood and thus feed more quickly. The aim of this work was to investigate to what extent strictly telmophagous insects such as tsetse flies are exposed to thermal stress during feeding and consequently to evaluate the impact of the feeding strategy on the exposition to overheating in haematophagous insects in general. Real time thermographic analysis during feeding revealed that the flies’ body significantly heat up quite homogeneously. At the end of feeding, however, a marked regional heterothermy occurs as a consequence of the alary muscles warm up that precedes take-off. Feeding strategies, either solenophagy or telmophagy, thus appear to have a great impact on both exposition to predation risks and to thermal stress.     

Biophysical Ecology and Heat Exchange in Insects

When used with observations of behavior and physiology of animalsin known microclimates, a biophysical approach is a powerfultool for predicting body temperatures of insects. For ectothermicinsects, solution of the energy budget equation and use of operativetemperature models have been used to determine the range oftemperatures which an insect can exhibit in a given environment.Knowledge of body temperature has allowed predictions of whenimportant behaviors arepossible in the field, thereby directlyrelating biophysical models to fitness parameters of animals.A proper understanding of the physiological mechanism(s) controllingheat exchange is prerequisite to application and interpretationof information obtained using biophysical techniques. For endothermicinsects, physiological regulation of heat exchange forces amore complicated analysis. Evaluation of thoracic heat exchangealone (aside from indicating whether insects are regulatingT_th) is of little utility for either quantifying total heatexchange, or evaluating thermoregulatory mechanisms withoutfurther information. Further studies of biophysics and physiologyof endothermic insects during flight are needed to correct thesedeficiencies. Application of biophysical techniques has allowedpredictions of behavior of flying insects based onprinciplesof heat exchange which cannot be examined directly. Analysesof endothermy of restinghoneybee swarms and hives indicate thatthese "superorganisms" regulate temperature rather preciselyover a remarkable range of environmental temperature using mechanismsequivalent to thoseused by resting endothermic vertebrates.     

Genetic variation in heat-stress tolerance among South American <Emphasis Type="Italic">Drosophila</Emphasis> populations

Spatial or temporal differences in environmental variables, such as temperature, are ubiquitous in nature and impose stress on organisms. This is especially true for organisms that are isothermal with the environment, such as insects. Understanding the means by which insects respond to temperature and how they will react to novel changes in environmental temperature is important for understanding the adaptive capacity of populations and to predict future trajectories of evolutionary change. The organismal response to heat has been identified as an important environmental variable for insects that can dramatically influence life history characters and geographic range. In the current study we surveyed the amount of variation in heat tolerance among Drosophila melanogaster populations collected at diverse sites along a latitudinal gradient in Argentina (24°–38°S). This is the first study to quantify heat tolerance in South American populations and our work demonstrates that most of the populations surveyed have abundant within-population phenotypic variation, while still exhibiting significant variation among populations. The one exception was the most heat tolerant population that comes from a climate exhibiting the warmest annual mean temperature. All together our results suggest there is abundant genetic variation for heat-tolerance phenotypes within and among natural populations of Drosophila and this variation has likely been shaped by environmental temperature.     

Diversity of insect‐induced galls along a temperature– rainfall gradient in the tropical savannah region of the Northern Territory,Australia

Evidence regarding the effect of temperature and rainfall on gall‐inducing insects is contradictory: some studies indicate that species richness of gall‐inducing insects increases as environments become hotter and drier, while others suggest that these factors have no effect. The role of plant species richness in determining species richness of gall‐inducing insects is also controversial. These apparent inconsistencies may prove to be due to the influence of soil fertility and the uneven distribution of gall‐inducing insect species among plant taxa. The current study tested hypotheses about determinants of gall‐inducing insect species richness in a way different to previous studies. The number of gall‐inducing insect species, and the proportion of species with completely enclosed galls (more likely to give protection against heat stress and desiccation), were measured in replicate plots at five locations along a 500‐km N‐S transect in the seasonal tropics of the Northern Territory, Australia. There is a strong temperature–rainfall gradient along this transect during the wet season. Plant species lists had already been compiled for each collection plot. All plots were at low elevation in eucalypt savannah growing on infertile soils. There was no evidence to suggest that hot, dry environments in Australia have more gall‐inducing insect species than cooler, wetter environments, or that degree of enclosure of galls is related to protecting insects from heat stress and desiccation. The variable number of gall‐inducing insect species on galled plant species meant that plant species richness did not influence gall species richness. Confirmation is still required that low soil fertility does not mask temperature–rainfall effects and that galls in the study region are occupied predominantly in the wet season, when the temperature–rainfall gradient is most marked.     

Relative susceptibility of Tribolium confusum life stages exposed to elevated temperatures

Methyl bromide, a space fumigant used in food-processing facilities, may be phased out in the United States by 2005. The use of elevated temperatures or heat treatment is gaining popularity as a methyl bromide alternative. During heat treatment, the temperature of the whole food-processing facility, or a portion of it, is raised and held between 50 and 60 degrees C for 24-36 h to kill stored-product insects. We determined time-mortality responses of the confused flour beetle, Tribolium confusum (Jacquelin du Val), eggs, young larvae, old larvae, pupae, and adults exposed to six constant temperatures between 46 and 60 degrees C. Responses of all five insect stages also were measured using exposure times of 160, 40, and 12 min at 46, 50, and 60 degrees C, respectively. Time-mortality responses of all T. confusum life stages increased with an increase in exposure time and temperature. Both time-mortality and fixed time responses showed eggs and young larvae to be most susceptible at elevated temperatures and old larvae to be least susceptible. Our results suggest that old larvae should be used as test insects to gauge heat treatment effectiveness, because heat treatment aimed at controlling old larvae should be able to control all other T. confusum life stages. Besides providing baseline data for successful use of heat treatments, time-mortality data collected at the six temperatures can be used for developing thermal death kinetic models for this species to predict mortality during actual facility heat treatments.     

Insect responses to heat: physiological mechanisms,evolution and ecological implications in a warming world

Surviving changing climate conditions is particularly difficult for organisms such as insects that depend on environmental temperature to regulate their physiological functions. Insects are extremely threatened by global warming, since many do not have enough physiological tolerance even to survive continuous exposure to the current maximum temperatures experienced in their habitats. Here, we review literature on the physiological mechanisms that regulate responses to heat and provide heat tolerance in insects: (i) neuronal mechanisms to detect and respond to heat; (ii) metabolic responses to heat; (iii) thermoregulation; (iv) stress responses to tolerate heat; and (v) hormones that coordinate developmental and behavioural responses at warm temperatures. Our review shows that, apart from the stress response mediated by heat shock proteins, the physiological mechanisms of heat tolerance in insects remain poorly studied. Based on life‐history theory, we discuss the costs of heat tolerance and the potential evolutionary mechanisms driving insect adaptations to high temperatures. Some insects may deal with ongoing global warming by the joint action of phenotypic plasticity and genetic adaptation. Plastic responses are limited and may not be by themselves enough to withstand ongoing warming trends. Although the evidence is still scarce and deserves further research in different insect taxa, genetic adaptation to high temperatures may result from rapid evolution. Finally, we emphasize the importance of incorporating physiological information for modelling species distributions and ecological interactions under global warming scenarios. This review identifies several open questions to improve our understanding of how insects respond physiologically to heat and the evolutionary and ecological consequences of those responses. Further lines of research are suggested at the species, order and class levels, with experimental and analytical approaches such as artificial selection, quantitative genetics and comparative analyses.     

Validity of thermal ramping assays used to assess thermal tolerance in arthropods

Proper assessment of environmental resistance of animals is critical for the ability of researchers to understand how variation in environmental conditions influence population and species abundance. This is also the case for studies of upper thermal limits in insects, where researchers studying animals under laboratory conditions must select appropriate methodology on which conclusions can be drawn. Ideally these methods should precisely estimate the trait of interest and also be biological meaningful. In an attempt to develop such tests it has been proposed that thermal ramping assays are useful assays for small insects because they incorporate an ecologically relevant gradual temperature change. However, recent model-based papers have suggested that estimates of thermal resistance may be strongly confounded by simultaneous starvation and dehydration stress. In the present study we empirically test these model predictions using two sets of independent experiments. We clearly demonstrate that results from ramping assays of small insects (Drosophila melanogaster) are not compromised by starvation- or dehydration-stress. Firstly we show that the mild disturbance of water and energy balance of D. melanogaster experienced during the ramping tests does not confound heat tolerance estimates. Secondly we show that flies pre-exposed to starvation and dehydration have "normal" heat tolerance and that resistance to heat stress is independent of the energetic and water status of the flies. On the basis of our results we discuss the assumptions used in recent model papers and present arguments as to why the ramping assay is both a valid and ecologically relevant way to measure thermal resistance in insects.     

Thermal physiological ecology of Colias butterflies in flight

Summary As a comparison to the many studies of larger flying insects, we carried out an initial study of heat balance and thermal dependence of flight of a small butterfly (Colias) in a wind tunnel and in the wild.Unlike many larger, or facultatively endothermic insects, Colias do not regulate heat loss by altering hemolymph circulation between thorax and abdomen as a function of body temperature. During flight, thermal excess of the abdomen above ambient temperature is weakly but consistently coupled to that of the thorax. Total heat loss is best expressed as the sum of heat loss from the head and thorex combined plus heat loss from the abdomen because the whole body is not isothermal. Convective cooling is a simple linear function of the square root of air speed from 0.2 to 2.0 m/s in the wind tunnel. Solar heat flux is the main source of heat gain in flight, just as it is the exclusive source for warmup at rest. The balance of heat gain from sunlight versus heat loss from convection and radiation does not appear to change by more than a few percent between the wings-closed basking posture and the variable opening of wings in flight, although several aspects require further study. Heat generation by action of the flight muscles is small (on the order of 100 m W/g tissue) compared to values reported for other strongly flying insects. Colias appears to have only very limited capacity to modulate flight performance. Wing beat frequency varies from 12–19 Hz depending on body mass, air speed, and thoracic temperature. At suboptimal flight temperatures, wing beat frequency increases significantly with thoracic temperature and body mass but is independent of air speed. Within the reported thermal optimum of 35–39°C, wing beat frequency is negatively dependent on air speed at values above 1.5 m/s, but independent of mass and body temperature. Flight preference of butterflies in the wind tunnel is for air speeds of 0.5–1.5 m/s, and no flight occurs at or above 2.5 m/s. Voluntary flight initiation in the wild occurs only at air speeds 1.4 m/s.In the field, Colias fly just above the vegetation at body temperatures of 1–2°C greater than when basking at the top of the vegetation. These measurements are consistent with our findings on low heat gain from muscular activity during flight. Basking temperatures of butterflies sheltered from the wind within the vegetation were 1–2°C greater than flight temperatures at vegetation height.     

Adaptations to low temperature in high altitude insects from Mount Kenya

Abstract. 1. The strategies for low temperature survival in insects on Mount Kenya were investigated. The insects were collected from their natural habitats and their supercooling points and low temperature tolerances determined.
2. Most insects showed no special adaptations to low temperature survival and seem to depend on spending the cold nights in protected habitats, such as beneath stones and fallen trunks of plants, as well as within the wet frills of dead leaves of alpine plants, where they are protected by the heat released from freezing water.
3. Some insects, e.g. Collembola, aphids and a curculionid beetle, which live in relatively unprotected habitats, had low supercooling points, allowing them to remain unfrozen when exposed to low night temperatures. A nucleator free diet is apparently essential for the survival of such species.
4. Two species of curculionid beetles were found to withstand freezing down to -7C. These beetles had nucleating agents in their haemolymph and higher supercooling points than most of the other species studied.
5. A moderate freezing tolerance was found in larvae of a midge that lives in the watery liquid between the leaves of Senecio brassica .     

The effects of temperature on host-pathogen interactions in D. melanogaster: who benefits?

Drosophila melanogaster is widely used to study immune system function in insects. However, little work has been done in D. melanogaster on the effect of temperature on the immune system. Here we describe experiments that demonstrate that cooler temperatures enhance survival after infection and alter expression of immune-related genes in flies. This effect appears to be due not only to the fact that colder temperatures slow down bacterial growth, but also to the beneficial effects of cooler temperature on immune function. We explore the possibility that heat shock proteins, and in particular, Hsp83, may improve immune function at cool temperatures. We have long known that temperature can alter immune responses against microbial pathogens in insects. The approach described here allows us to determine whether this effect is due primarily to temperature-specific effects on the host or on its pathogen. These results suggest that both may be important.     

Warming rates as a function of body size in periodic endotherms

Summary Warm-up rates and cooling constants were measured in several groups of insects over a wide range of thoracic weights. Vertebrate heterotherms show an inverse dependence of warm-up rate on body weight, but in insects warm-up rate increases with increasing size over the range studied (Figures 1-4, 8). Equations are derived, based on known or estimated relations of heat loss and production to body weight, that predict warm-up rates in insects and mammals with reasonable accuracy. Both weight-specific heat production and loss increase with decreasing body size, but heat loss increases more rapidly. At the size range of insects, loss is so rapid that metabolism cannot fully compensate. Then warm-up rate is constant or decreases with diminishing size.     

Thermoregulation and daily activity patterns in a black desert grasshopper,Taeniopoda eques

Behavioural thermoregulation was studied in the western horse lubber grasshopper Taeniopoda eques (Burmeister), a native of the Chihuahuan Desert of North America. The grasshoppers regulated their temperature through a series of daily cyclical vertical movements between vegetation and the soil, and by the adoption of four thermoregulatory postures: flanking, crouching, stilting and stem-shading. At dawn, the grasshoppers moved from their nocturnal roost-plants to the ground, returned to bushes during the middle of the day, moved back to the open ground in the afternoon, then reascended vegetation at dusk. The occurrences of the four thermoregulatory postures were synchronized with these microhabitat shifts. During the cooler mornings and afternoons, the insects maximized heat gain by flanking and crouching, achieving thoracic temperatures of up to 16°C above ambient. Throughout the hot middle of the day the insects stilted and shaded, minimizing heat gain. These behaviours effectively kept the grasshoppers' body temperatures near the preferred temperature (36·2°C), but lower than the maximum voluntarily tolerated temperature (41·9°C), critical thermal maximum (45·2°C) and instantaneous lethal maximum (46·5°C). The body size of flanking insects influenced heating and cooling rates, wind effects and temperature excess at equilibrium. Both infrared and visible radiation appeared to elicit flanking. The need and ability to thermoregulate are influenced by this insect's reliance on chemical deterrents for defence.     

Rapid thermal adaptation during field temperature variations in Drosophila melanogaster

Under natural conditions, the fruit fly (Drosophila melanogaster) is constantly exposed to variations in temperature and light. Laboratory investigations have demonstrated that D. melanogaster and other insects adapt quickly to temperature variations, but only few studies have investigated this ability under natural temperature variations. Here we placed laboratory raised female D. melanogaster in field cages and exposed them to natural variations in light and temperature over a 2 day period (temperature range: 12–25 °C). During this period we sampled flies every 6 h and measured their ability to survive heat and cold shock. There was a significant positive correlation between field temperature and heat shock survival and a significant negative correlation between field temperature and cold shock survival indicating that D. melanogaster are constantly adapting to their surrounding environment. The results also suggest that heat and cold resistance are obtained at a cost as these two traits were negatively correlated.     

Local adaptation of reproductive performance during thermal stress

Considerable evidence exists for local adaptation of critical thermal limits in ectotherms following adult temperature stress, but fewer studies have tested for local adaptation of sublethal heat stress effects across life‐history stages. In organisms with complex life cycles, such as holometabolous insects, heat stress during juvenile stages may severely impact gametogenesis, having downstream consequences on reproductive performance that may be mediated by local adaptation, although this is rarely studied. Here, we tested how exposure to either benign or heat stress temperature during juvenile and adult stages, either independently or combined, influences egg‐to‐adult viability, adult sperm motility and fertility in high‐ and low‐latitude populations of Drosophila subobscura. We found both population‐ and temperature‐specific effects on survival and sperm motility; juvenile heat stress decreased survival and subsequent sperm motility and each trait was lower in the northern population. We found an interaction between population and temperature on fertility following application of juvenile heat stress; although fertility was negatively impacted in both populations, the southern population was less affected. When the adult stage was also subject to heat stress, the southern population exhibited positive carry‐over effects whereas the northern population's fertility remained low. Thus, the northern population is more susceptible to sublethal reproductive consequences following exposure to juvenile heat stress. This may be common in other organisms with complex life cycles and current models predicting population responses to climate change, which do not take into account the impact of juvenile heat stress on reproductive performance, may be too conservative.     

Mathematical modeling of the temperature field distribution in insect winter clusters

A model is proposed for the distribution of temperature fields and mechanisms of thermoregulation in an insect (honeybee) cluster self-organizing for protection against long-term cooling. The winter cluster is an ordered system of heat generation, accumulation, and dissipation. Estimates are obtained for the influence of ambient temperature that promotes clustering and of the number of clustered insects on the efficiency of cold protection. Described are the dynamic links between the cluster structures that ensure minimal energy expenditures in metabolism and thermoregulation; this allows the cluster to withstand the long unfavorable exposure to temperature varying far beyond the limits of viability for an individual insect.     

Behavioral thermoregulation inpalmipenna aeoleoptera (neuroptera): Do the hypertrophied hindwings play a role?

The hypertrophied hindwings of Palmipenna aeoleoptera (Neuroptera) were examined for a possible thermoregulatory role. These wings arise from basal stalks which expand into large, flattened, darkly pigmented, and vascularized dilations. During the cooler times of the day the insects basked by crouching with the body and hindwings held horizontally in contact with rocks. As air temperatures increased, insects stilted with the hindwings held at 90° to the horizontal. Thoracic temperatures of these ectotherms correlated with air temperatures (T_thorax = 1.55T_air –10.99), with maximum recorded thoracic temperatures of 47°C. No differences were found between thoracic temperatures of males and those of females, although males had far larger hindwings. Live insects caught on rocks were consistently cooler than dead insects (operational temperature thermometers) on rocks. This may be attributed to convective cooling in flight just prior to capture, and stilting, behavior patterns that were frequent during the hottest times of the day. Thoracic temperatures of insects resting on rocks were frequently higher than operational temperature thermometers in air, suggesting that warming resulted from basking on rocks. The minimum body temperature for flight was 27°C. In the laboratory, hindwing ablation altered neither the rate (using time constants) of heating or cooling nor the equilibrium temperature of the body, showing that the hindwings play no direct role in heat uptake or loss.     

中华蜜蜂ZFP37基因的生物信息学分析及高温下表达特性的研究

锌指蛋白(Zinc finger proteins, ZFPs)是一类在真核生物体内广泛分布的蛋白质。锌指蛋白作为一类转录因子,它能够调控基因的表达和细胞的分化,最近的研究显示其在动植物抗逆方面也发挥着重要作用。本研究对中华蜜蜂Apis cerana cerana ZFP37的蛋白结构进行了预测分析,并通过qRT-PCR分析了中华蜜蜂在遭受高温胁迫时ZFP37的表达情况,进一步了解锌指蛋白在中华蜜蜂应对热胁迫过程中的作用。结果显示,中华蜜蜂ZFP37可编码123个氨基酸,蛋白分子量为13.7 kDa,无跨膜结构。氨基酸同源序列比对结果表明,中华蜜蜂ZFP37序列与蜜蜂科昆虫的相似性最高,与其他膜翅目昆虫的相似性存在差异。基因的表达模式显示,ZFP37在高温下表达升高,此外,胁迫时间的增加也可导致ZFP37表达的升高。这些结果表明ZFP37对于中华蜜蜂应对热应激有重要的生物学意义。     

连续温度梯度下昆虫趋温性的研究现状与展望

昆虫作为一种能够自由活动的生物,可以通过运动主动选择对其有利的环境温度。大多数研究中昆虫被迫接受人为设定的恒温或变温,并未体现出昆虫本身对适宜温度的主动选择性。连续温度梯度是在某一介质的两端产生由高到低连续变化的温度范围。在一定温度梯度中昆虫趋温行为的研究揭示了其主动选择的适宜温度,这对了解昆虫的空间动态、提高测报准确性和开发防治新方法有重要意义。总结了产生连续温度梯度的各种装置,致冷、加热和温度测量方法以及昆虫趋温行为的观察装置和方法,包括在植物体上(内)及空气、下垫面、粮食和土壤等介质中产生温度梯度的方法及装置。各装置以水浴或电器设备制冷或加热,肉眼观察手工记录或以摄像机、声音信号采集系统等方法记录昆虫的行为。综述了多种昆虫生长发育、栖息、产卵或取食的偏好温度,总结了性别、发育阶段和生态型等生理因素及光照、湿度和预适应温度等环境因子对昆虫偏好温度变化的影响。昆虫的趋温性因种而异,同种昆虫不同发育阶段或不同生命活动所趋温度不同。多数种类昆虫雄性成虫的偏好温度比雌性略高。某些昆虫的多型现象可能导致其种内不同生态型的偏好温度存在差异。光照和湿度的变化会影响某些昆虫对温度的反应。有些昆虫经预适应温度训练后,其偏好温度发生改变。某些昆虫对温度的偏好呈现出一定的日变化和季节变化规律。饥饿条件下昆虫的偏好温度降低。温度梯度的有无及其方向、温度的高低、温差的大小等因素都会影响昆虫的活动性。最后分析了本类研究中存在的问题和不足,并展望了未来的研究方向,指出开展对重要农林作物害虫和天敌趋温行为及其生理学机制,外界环境因素影响昆虫趋温性等方面的探索将是未来该领域研究的重点内容。     

A review of the energetics of pollination biology

Pollination biology is often associated with mutualistic interactions between plants and their animal pollen vectors, with energy rewards as the foundation for co-evolution. Energy is supplied as food (often nectar from flowers) or as heat (in sun-tracking or thermogenic plants). The requirements of pollinators for these resources depend on many factors, including the costs of living, locomotion, thermoregulation and behaviour, all of which are influenced by body size. These requirements are modified by the availability of energy offered by plants and environmental conditions. Endothermic insects, birds and bats are very effective, because they move faster and are more independent of environmental temperatures, than are ectothermic insects, but they are energetically costly for the plant. The body size of endothermic pollinators appears to be influenced by opposing requirements of the animals and plants. Large body size is advantageous for endotherms to retain heat. However, plants select for small body size of endotherms, as energy costs of larger size are not matched by increases in flight speed. If high energy costs of endothermy cannot be met, birds and mammals employ daily torpor, and large insects reduce the frequency of facultative endothermy. Energy uptake can be limited by the time required to absorb the energy or eliminate the excess water that comes with it. It can also be influenced by variations in climate that determine temperature and flowering season.     

Thermoregulation and the effect of body temperature on call temporal parameters in the cicada Diceroprocta olympusa (Homoptera: Cicadidae)

We investigated the thermoregulatory behavior, thermal responses (minimum flight, maximum voluntary tolerance and heat torpor temperatures) and the effect of body temperature (T(b)) on call parameters in the cicada Diceroprocta olympusa (Walker). Regression of T(b) as a function of ambient (T(a)) or perch temperatures (T(p)) suggests thermoregulation is occurring. Thermoregulation occurs through behavioral changes that alter the uptake of solar radiation. T(p) is a better predictor of T(b) than is T(a). Thermal responses (minimum flight temperature 20.4 degrees C, maximum voluntary tolerance temperature 37 degrees C, and heat torpor temperature 46.7 degrees C) may be related to the humid, grassland habitat of the species. In contrast to other acoustic insects, no significant relationship was found between the temporal parameters of the calling song and T(b) within the population of D. olympusa.