Thermoregulation behaviour in codling moth larvae

Abstract. The thermoregulation behaviour of the codling moth, Cydia pomonella, is investigated in temperature gradient experiments with larvae feeding within apples, and with mature larvae searching for cocooning sites. Feeding larvae appear to prefer the apple hemisphere with a higher temperature (i.e. they build larger cavities in the radiated, warmer part of the fruit). The proportion of larval cavities in the warmer hemisphere is positively related to increasing apple temperature on that side, as well as to the temperature difference between the warm and the cool fruit hemisphere. The mechanism in feeding larvae can be termed as cryptic basking because, during microhabitat selection, the caterpillars exploit temperature differences that are caused explicitly by incident solar radiation. Fifth-instar larvae in search of cocooning sites show no temperature preference within the large gradient offered (9–29 °C), with no difference between males and females. During larval development, the insect changes its thermoregulation behaviour in response to a possible shift in benefits of an elevated body temperature with respect to environmental conditions. Both the thermoregulation behaviour and such a shift of behavioural response should be respected when simulating body temperatures of the species.     

Opposite effect of capsaicin and capsazepine on behavioral thermoregulation in insects

Transient receptor potential channels are implicated in thermosensation both in mammals and insects. The aim of our study was to assess the effect of mammalian vanilloid receptor subtype 1 (TRPV1) agonist (capsaicin) and antagonist (capsazepine) on insect behavioral thermoregulation. We tested behavioral thermoregulation of mealworms larvae intoxicated with capsaicin and capsazepine in two concentrations (10⁻⁷ and 10⁻⁴ M) in a thermal gradient system for 3 days. Our results revealed that in low concentration, capsaicin induces seeking lower temperatures than the ones selected by the insects that were not intoxicated. After application of capsazepine in the same concentration, the mealworms prefer higher temperatures than the control group. The observed opposite effect of TRPV1 agonist and antagonist on insect behavioral thermoregulation, which is similar to the effect of these substances on thermoregulation in mammals, indicates indirectly that capsaicin may act on receptors in insects that are functionally similar to TRPV1.     

Physiological variation in insects: large-scale patterns and their implications

In this paper we demonstrate how broad scale comparative physiology has an important role to play in informing a variety of assumptions made in macroecology. We do so by examining large-scale geographic variation in insect development, thermal tolerance and metabolic rate. From these studies, and those from the literature on insect water loss and thermoregulation, we show that there is often a bias to the geographic extent of available empirical data. Studies of cold hardiness are most usually undertaken at high latitudes, while investigations of upper thermal tolerances and water loss are most common in warm arid regions. Likewise, we demonstrate that much variation in insect physiological tolerances is partitioned at higher taxonomic levels, which has important implications for comparative physiology. Intriguingly, data on the full range of variables we review are available for only three species. We also show that, despite its importance, body size is regularly reported in only some kinds of investigations (metabolic rate, water loss rate), whereas in others (upper lethal temperature, cold hardiness, development) this variable is often ignored. In short, although large-scale comparative physiology can contribute considerable understanding to both physiology and ecology, there is much that remains to be done.     

Host thermal biology: the key to understanding host–pathogen interactions and microbial pest control?

1 The role of pathogens in insect population dynamics remains poorly understood and their performance in biological control is erratic. Here we identify that temperature and host thermal behaviour, both the active interaction with environmental temperature and solar radiation via thermoregulation and the passive interception of these factors by thermal generalists, are central to understanding host–pathogen interactions. 2 We demonstrate that pathogenicity, the latent period of infection and host recovery rate can all vary dramatically across and between seasons due to thermal biology of the host and changes in environmental temperature. 3 Such effects have not been thoroughly explored in any previous investigations but may have major implications for disease dynamics in insects and possibly in ectotherms in general, and for development of effective biopesticides.     

Physiological mechanisms of thermoregulation in reptiles: a review

The thermal dependence of biochemical reaction rates means that many animals regulate their body temperature so that fluctuations in body temperature are small compared to environmental temperature fluctuations. Thermoregulation is a complex process that involves sensing of the environment, and subsequent processing of the environmental information. We suggest that the physiological mechanisms that facilitate thermoregulation transcend phylogenetic boundaries. Reptiles are primarily used as model organisms for ecological and evolutionary research and, unlike in mammals, the physiological basis of many aspects in thermoregulation remains obscure. Here, we review recent research on regulation of body temperature, thermoreception, body temperature set-points, and cardiovascular control of heating and cooling in reptiles. The aim of this review is to place physiological thermoregulation of reptiles in a wider phylogenetic context. Future research on reptilian thermoregulation should focus on the pathways that connect peripheral sensing to central processing which will ultimately lead to the thermoregulatory response.     

Highly‐enhanced larval growth during the cold season mediated by the basking behavior of the butterfly Parnassius citrinarius (Lepidoptera: Papilionidae)

Some insect species are thought to grow quickly, even in low temperatures under natural conditions, presumably by conducting basking behaviors to use sunlight. However, whether basking behavior in fact enhances developmental speed and shortens the larval period in the field has not been determined. Moreover, few studies have examined whether basking is behavioral thermoregulation or simply the result of highly‐heterogeneous heat environments in the field. To examine these issues, we conducted field observations and laboratory experiments using larvae of Parnassius citrinarius Motschulsky, which mature within a short period after the thaw in early spring. First, body temperatures of larvae were measured under sunny and cloudy conditions. Second, larval preference for warmer locations was examined. Finally, we compared the developmental speed of larvae when they basked under field conditions and when did not bask in laboratory conditions under different air temperature regimes. Under sunny conditions, larval body temperature was substantially higher than either the temperature of the host plant or the air temperature, and was equivalent to the temperature of dead leaves, which the larvae used as basking sites. In contrast, no such tendency was observed under cloudy conditions. Larvae exhibited an exclusive preference for warmer locations. Moreover, in the field, despite the low ambient temperature, larvae grew much faster than those reared in the laboratory. These results imply that the basking behavior of P. citrinarius larvae is active thermoregulation to maintain high body temperatures in the cold season.     

Modern theoretical and practical problems of homoiothermia and thermoregulation

The adjuncts to the existing determinations of homoiothermia are made on the basis of new data, the principles of temperature adaptation of humans and homoiothermal animals are presented. The main purposes of the thermoregulation system of homoiothermal animals and humans in various temperature excesses are formulated. The arguments are advanced in favor of the fact that in the thermoneutral zone the thermoregulation system goes from the principles of regulating the temperature homeostasis by one or several temperature points of a body to the regulation by the fluctuations of the total heat content of an organism, which increases the sensitivity and the accuracy of the thermoregulation system operation. The physiological mechanisms are described of determining (measuring) the total heat content of a body.     

Into thin air: Physiology and evolution of alpine insects

Numerous physical parameters that influence insect physiologyvary substantially with altitude, including temperature, airdensity, and oxygen partial pressure. Here, we review existingliterature and present new empirical data to better characterizethe high-altitude environment, and then consider how this environmentaffects the physiology and evolution of insects. Using weatherballoon data from fifty-three sites across the globe, we estimatea mean altitudinal temperature lapse rate of 6.0 °C/km.We also present empirically determined lapse rates for P_O2 andair density. The temperature decline with elevation may substantiallycompromise insect thermoregulation at high altitude. However,heat-transfer models predict that lower air density at elevationreduces convective heat loss of insects by to a surprisinglylarge degree. This effect combined with behavioral thermoregulationand the availability of buffered microhabitats make the netthermal consequences of high-altitude residence strongly context-specific.The decline in P_O2 with elevation may compromise insect developmentand physiology, but its effects are difficult to predict withoutsimultaneously considering temperature and air density. Flyinginsects compensate for low air densities with both short-termresponses, such as increased stroke amplitude (but not wingbeatfrequency), and with long-term developmental and/or evolutionaryincreases in wing size relative to body size. Finally, in contrastto predictions based on Bergmann's Rule, a literature surveyof thirty-six insect species suggests that those living in colder,higher altitudes do not tend to have larger body sizes.     

Thermoregulation in the comfort temperature zone

Under constant adequate temperature conditions (comfortable for a man) the retention of temperature homeostasis was shown to require a continuous functioning of the physiological thermoregulation system to prevent short-term and whole day deviations of the temperature from the physiological level. Under adequate temperature conditions the thermoregulation system was shown to attain its highest sensitivity and accuracy. It is possible that this occurs owing to physiological control over the total body heat content being included into the process of thermoregulation. The data are given on the existence and "structure" of the physiological mechanisms of such a control.     

Behavioural and autonomic thermoregulation in lean and genetically obese (ob/ob) mice

1. 1.|The capacity for behavioural thermoregulation has been assessed in lean and genetically obese (ob/ob) mice, using operant conditioning.

2. 2.|After 30 min at an initial air temperature (T_a) of 0°C, total thermal reinforcements and T_a were greater in ob/ob than lean mice; deep body temperature increased in both genotypes. Without a heater, body temperature in the ob/ob fell markedly in the cold.

3. 3.|Behavioural thermoregulation also depended on food intake and test temperature. i]4.|The capacity for behavioural thermoregulation is thus unimpaired in the ob/ob mouse, unlike that for autonomic thermoregulation, suggesting separate sets of central controls for the two thermoregulatory systems.

Thermoregulatory abilities of Alaskan bees: effects of size, phylogeny and ecology

1. The thermoregulatory capabilities of 18 species of Alaskan bees spanning nearly two orders of magnitude of body mass were measured. Thoracic temperature, measured across the temperature range at which each species forages, was regressed against operative (environmental) temperature to determine bees' abilities to maintain relatively constant thoracic temperatures across a range of operative temperatures (thermoregulatory performance).
2. Previous studies on insect thermoregulation have compared thoracic temperature with ambient air temperature. Operative temperature, which integrates air temperature, solar radiation and effects of wind, was estimated by measuring the temperature of a fresh, dead bee in the field environment. It is suggested that this is a more accurate measure of the thermal environment experienced by the insect and also allows direct comparisons of insects under different microclimate conditions, such as in sun and shade.
3. Simple regression analysis of species and family means, and analysis of phylogenetically based independent contrasts showed thermoregulatory capability, ability to elevate thoracic temperature, and minimum thoracic temperature necessary for initiating flight all increased with body size.
4. Bumble-bees were better thermoregulators than solitary bees primarily as a consequence of their larger body size. However, their thermoregulatory abilities were slightly, but significantly, better than predicted from body size alone, suggesting an added role of pelage and/or physiology. Large solitary bees were better thermoregulators than small solitary bees apparently as a result of body-size differences, with small bees acting as thermal conformers.     

Communication by electrical means in social insects

Social insects, belonging to the order Hymenoptera, maintain a fixed, optimal temperature in their nest. Thus, in social wasps and hornets, the optimal nest temperature is 29 degrees C, despite the fact that they are distributed in regions of varying climates both in the northern and southern hemispheres of the globe. Since hornets and bees are relatively small insects, determination of their own body temperature as well as that of their nest and the brood was made via thermometers or by the use of infrared (IR) rays. It has been suggested that thermoregulation in social insect colonies is effected primarily by the adult insects via muscle activation, that is, fluttering of their wings, which can raise both their own and the ambient temperature by many degrees centigrade. However, the larval brood can also contribute to the thermoregulation by acting as heat resources and thereby raising the ambient temperature by 1-2 degrees C. To this end, the adult hornets are endowed with a well-developed musculature and their larvae, too, have muscles that enable them to move about. Not so the hornet pupae which are enclosed in a silk envelope (the cocoon), with a rather thick silk cap spun by the pupating larvae, and have rather undeveloped muscles. In the latter instance, it stands to reason that the pupae benefit from the nest warming achieved primarily by the adult hornets, but how is the information regarding their thermal needs relayed from them to the adults? Previously we showed that the adult hornets are attracted to the pupae by pheromones released by the latter, but such chemical compounds can only convey information of a general nature and we are still left with the question as to how the adult hornet can gauge or ascertain the temperature of a single insulated pupa. The present study provides evidence that the hornet pupa can indeed transmit information regarding its body temperature via electrical means.     

An alternative heat-budget model relevant to heat transfer in fishes and its practical use for detecting their physiological thermoregulation

Previous studies have detected activity-independent fish thermoregulation or conservation mechanisms by applying a mathematical model to body temperature data collected with electronic tags. This model is inadequate, due to its inability to separate quantitatively the effects of physiological thermoregulation from those of physical thermal inertia (the low thermal conductance of the body). In this paper, we have developed an alternative mathematical model that separates these effects. We have then applied it to published electronic tagging data from a large, free-swimming blue shark, Prinoca glauca, to demonstrate physiological thermoregulation. Resultant estimated body-temperature curves indicate that the fish could adjust its whole-body heat-transfer coefficient by changes in arterial blood flow over a range of one order of magnitude. To look at the physical effect on thermoregulation, body temperature for a smaller hypothetical fish was calculated. The estimated temperature was significantly lower than the actual value, indicating that an ectothermic fish like the blue shark cannot achieve physiological thermoregulation without assistance from thermal inertia. In addition, the blue shark returns to cooler depths without recovering its body temperature to the normal surface-temperature level, indicating that this behavior contributes to maximization of the rate of body-temperature recovery. Furthermore, the model indicated that the time for body-temperature recovery is irrelevant to the initial body temperature. Thus, the model made it possible to quantify thermophysiological manipulation. In addition, it was also useful in the comparison of thermoregulatory mechanisms between fishes of different sizes or species.     

Incorporating neurophysiological concepts in mathematical thermoregulation models

Skin blood flow (SBF) is a key player in human thermoregulation during mild thermal challenges. Various numerical models of SBF regulation exist. However, none explicitly incorporates the neurophysiology of thermal reception. This study tested a new SBF model that is in line with experimental data on thermal reception and the neurophysiological pathways involved in thermoregulatory SBF control. Additionally, a numerical thermoregulation model was used as a platform to test the function of the neurophysiological SBF model for skin temperature simulation. The prediction-error of the SBF-model was quantified by root-mean-squared-residual (RMSR) between simulations and experimental measurement data. Measurement data consisted of SBF (abdomen, forearm, hand), core and skin temperature recordings of young males during three transient thermal challenges (1 development and 2 validation). Additionally, ThermoSEM, a thermoregulation model, was used to simulate body temperatures using the new neurophysiological SBF-model. The RMSR between simulated and measured mean skin temperature was used to validate the model. The neurophysiological model predicted SBF with an accuracy of RMSR?<?0.27. Tskin simulation results were within 0.37 °C of the measured mean skin temperature. This study shows that (1) thermal reception and neurophysiological pathways involved in thermoregulatory SBF control can be captured in a mathematical model, and (2) human thermoregulation models can be equipped with SBF control functions that are based on neurophysiology without loss of performance. The neurophysiological approach in modelling thermoregulation is favourable over engineering approaches because it is more in line with the underlying physiology.     

Thermal ecology and behaviour of the nomadic social forager Malacosoma disstria

The present study examines whether the nomadic social caterpillar Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae) can thermoregulate despite the lack of a tent, and evaluates the role of thermoregulation in directing the colony's behaviour. The presence of a radiant heat and light source (i.e. a lamp in the laboratory experiments and the sun in the field observations) enables caterpillar colonies to increase body temperature by basking (remaining still under a heat source) and this is only effective when caterpillars cluster in groups. Body temperatures achieved when basking in a group coincide with the temperatures at which the development rate is maximal for this species. Indeed, in the laboratory experiments, the presence of a lamp results in higher growth rates, confirming that thermoregulation is an advantage to group living. When a radiant heat/light source is provided at a distance from the food in the laboratory, caterpillars behave to maximize thermal gains: colonies move away from the food to bivouac (i.e. group together and remain still on a silk mat) under the lamp, spend more time on the bivouac and cluster in a more cohesive group. Thermal needs thus influence habitat selection and colony aggregation. Malacosoma disstria relies on developing rapidly, despite low seasonal temperatures, aiming to benefit from springtime high food quality and low predation rates; however, unlike others in its genus, it does not build a tent but instead exhibits collective nomadic foraging (i.e. the whole colony moves together between temporary resting and feeding sites). In this species, collective thermoregulatory behaviour is not only possible and advantageous, but also drives much of the colony's behaviour, in large part dictating the temporal and spatial patterns of movement. These findings suggest that thermoregulation may be an important selection pressure keeping colonies together.     

A perspective on insect–microbe holobionts facing thermal fluctuations in a climate-change context

Temperature influences the ecology and evolution of insects and their symbionts by impacting each partner independently and their interactions, considering the holobiont as a primary unit of selection. There are sound data about the responses of these partnerships to constant temperatures and sporadic thermal stress (mostly heat shock). However, the current understanding of the thermal ecology of insect–microbe holobionts remains patchy because the complex thermal fluctuations (at different spatial and temporal scales) experienced by these organisms in nature have often been overlooked experimentally. This may drastically constrain our ability to predict the fate of mutualistic interactions under climate change, which will alter both mean temperatures and thermal variability. Here, we tackle down these issues by focusing on the effects of temperature fluctuations on the evolutionary ecology of insect–microbe holobionts. We propose potentially worth-investigating research avenues to (i) evaluate the relevance of theoretical concepts used to predict the biological impacts of temperature fluctuations when applied to holobionts; (ii) acknowledge the plastic (behavioural thermoregulation, physiological acclimation) and genetic responses (evolution) expressed by holobionts in fluctuating thermal environments; and (iii) explore the potential impacts of previously unconsidered patterns of temperature fluctuations on the outcomes and the dynamic of these insect–microbe associations.     

Conserved roles of Osiris genes in insect development,polymorphism and protection

Much of the variation among insects is derived from the different ways that chitin has been moulded to form rigid structures, both internal and external. In this study, we identify a highly conserved expression pattern in an insect‐only gene family, the Osiris genes, that is essential for development, but also plays a significant role in phenotypic plasticity and in immunity/toxicity responses. The majority of Osiris genes exist in a highly syntenic cluster, and the cluster itself appears to have arisen very early in the evolution of insects. We used developmental gene expression in the fruit fly, Drosophila melanogaster, the bumble bee, Bombus terrestris, the harvester ant, Pogonomyrmex barbatus, and the wood ant, Formica exsecta, to compare patterns of Osiris gene expression both during development and between alternate caste phenotypes in the polymorphic social insects. Developmental gene expression of Osiris genes is highly conserved across species and correlated with gene location and evolutionary history. The social insect castes are highly divergent in pupal Osiris gene expression. Sets of co‐expressed genes that include Osiris genes are enriched in gene ontology terms related to chitin/cuticle and peptidase activity. Osiris genes are essential for cuticle formation in both embryos and pupae, and genes co‐expressed with Osiris genes affect wing development. Additionally, Osiris genes and those co‐expressed seem to play a conserved role in insect toxicology defences and digestion. Given their role in development, plasticity, and protection, we propose that the Osiris genes play a central role in insect adaptive evolution.     

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

For subterranean rodents, searching for food by extension of the tunnel system and maintenance of body temperature are two of the most important factors affecting their life underground. In this study we assess the effect of ambient temperature on energetics and thermoregulation during digging in Ctenomys talarum. We measured VO2 during digging and resting at ambient temperature (Ta) below, within, and above thermoneutrality. Digging metabolic rate was lowest at Ta within the thermoneutral zone and increased at both lower and higher temperatures, but body temperature (Tb) remained constant at all Tas. Below thermoneutrality, the cost of digging and thermoregulation are additive. Heat production for thermoregulation would be compensated by heat produced as a by-product of muscular activity during digging. Above thermoneutrality, conduction would be an important mechanism to maintain a constant Tb during digging.     

爬行动物胚胎的行为热调节

行为热调节是外温动物体温调节的主要方式。传统观点认为行为热调节仅存在于胚后阶段,然而近年来研究表明爬行动物胚胎具备行为热调节能力。本文回顾了爬行动物胚胎行为热调节的发现和研究进展,探讨了胚胎行为热调节的生态适应意义,分析了胚胎如何感知温度以完成行为热调节,指出了该领域的未来研究方向。