Insect thermoregulation

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The pre-flight warm-up behavior of a moth

Insect thermoregulation is the process whereby insects maintain body temperatures within certain boundaries. Insects have traditionally been considered as poikilotherms (animals in which body temperature is variable and dependent on ambient temperature) as opposed to being homeothermic (animals that maintain a stable internal body temperature regardless of external influences). However, the term temperature regulation, or thermoregulation , is currently used to describe the ability of insects and other animals to maintain a stable temperature (either above or below ambient temperature), at least in a portion of their bodies by physiological or behavioral means. [1] While many insects are ectotherms (animals in which their heat source is primarily from the environment), others are endotherms (animals that can produce heat internally by biochemical processes). These endothermic insects are better described as regional heterotherms because they are not uniformly endothermic. When heat is being produced, different temperatures are maintained in different parts of their bodies, for example, moths generate heat in their thorax prior to flight but the abdomen remains relatively cool. [2]

Contents

In-flight thermoregulation

Animal flight is a very energetically expensive form of locomotion that requires a high metabolic rate. In order for an animal to fly, its flight muscles need to be capable of high mechanical power output, which in turn, due to biochemical inefficiencies, end up producing large amounts of heat. [3] A flying insect produces heat, which, as long as it does not exceed an upper lethal limit, will be tolerated. However, if the flying insect is also exposed to external sources of heat (for example, radiation from the sun) or ambient temperatures are too high, it should be able to thermoregulate and stay in its temperature comfort zone. Higher speeds necessarily increase convective cooling. Higher flying velocities have been shown to result in an increase, instead of a reduction, of thoracic temperature. [4] This is probably caused by the flight muscles working at higher levels and consequently, increasing thoracic heat generation. The first evidence for insect thermoregulation in flight came from experiments in moths demonstrating that dissipation of heat occurs via hemolymph movement from the thorax to the abdomen. [5] The heart of these moths makes a loop through the center of the thorax facilitating heat exchange and converting the abdomen into both a heat sink and a heat radiator that helps the flying insect in maintaining a stable thoracic temperature under different ambient temperature conditions. It was believed that heat regulation was only achieved by varying heat loss until evidence for varying heat production was observed in honeybees. [6] Then, it was then suggested that thermal stability in honeybees, and probably many other heterothermic insects, was primarily attained by varying heat production. Whether flying insects are able or not to regulate their thoracic temperature by regulating heat production or only by varying heat loss, is still a matter of debate.

Pre-flight thermoregulation

Thoracic temperature changes in a moth recorded with an infra-red camera Insect warm-up.jpg
Thoracic temperature changes in a moth recorded with an infra-red camera

Several large insects have evolved to warm-up previous to flight so that energetically demanding activities, such as flight, are possible. [7] Insect behavior involves inefficient muscle operation that produces excess heat and establishes the thermal range in which specific muscles best function. The high metabolic cost of insect flight muscles means that great amounts of chemical energy are utilized by these specific muscles. However, only a very small percentage of this energy translates into actual mechanical work or wing movement. [3] Thus, the rest of this chemical energy is transformed into heat that in turn produces body temperatures significantly greater than those of the ambient.

These high temperatures at which flight muscles work impose a constraint on low temperature take-off because an insect at rest has its flight muscles at ambient temperature, which is not the optimal temperature for these muscles to function. So, heterothermic insects have adapted to make use of the excess heat produced by flight muscles to increase their thoracic temperature pre-flight. Both the dorsolongitudinal muscles (which flip down the wings during flight) and the dorsoventral muscles (which cause the wings to flip upward during flight) are involved in the pre-flight warm-up behavior but in a slightly different way. During flight, these function as antagonistic muscles to produce the wing flapping that allows for sustained flight. However, during warm-up these muscles are contracted simultaneously (or almost simultaneously in some insects) [8] to produce no wing movement (or a minimal amount of wing movement) and produce as much heat as possible to elevate thoracic temperatures to flight-levels. The pre-flight warm-up behavior of male moths ( Helicoverpa zea ) has been shown to be affected by olfactory information. [9] [10] [11] As in many moths, the males of this species respond to female pheromone by flying towards the female and trying to mate with her. During the warm-up of their flight muscles, and when in presence of the female pheromone, males generate heat at higher rates, so as to take off earlier and out-compete other males that might have also sensed the pheromone.

Achieving elevated temperatures as stated above fall under the term physiological thermoregulation because heat is generated by a physiological process inside the insect. The other described way of thermoregulation is called behavioral thermoregulation because body temperature is controlled by behavioral means, such as basking in the sun. Butterflies are a good example of insects that are heliotherms (deriving heat almost exclusively from the sun). [12]

Other thermoregulatory examples

Some nocturnal dung beetles have been shown to increase their ball-making and ball-rolling velocity when their thoracic temperature increases. [13] In these beetles, dung is a precious commodity that allows them to find a mate and feed their larvae. Discovering the resource soon is important so that they can start rolling a ball as soon as possible and take it to a distant place for burying. The beetles first detect the dung by olfactory cues and fly towards it rapidly. As they first arrive, their body temperatures are still high due to their flight metabolism, which allows them to make and roll balls faster; and the bigger the ball, the better chances they have of getting a mate. However, as time passes, a grounded beetle making a ball starts to cool off and it becomes harder to increase the size of the dung ball and also transport it. So, there is a trade-off between making a large ball that would guarantee a mate but might be not easily transported and a smaller ball, which might not attract a mate but can be safely taken to the burying place. Additionally, other beetles that arrive later (which are hotter), can actually fight over balls and have been shown to usually win against beetles that are cooler. [14]

Another example of thermoregulation is that of heat being used as a defensive mechanism. The Japanese honeybee ( Apis cerana japonica ) is preyed upon by a hornet ( Vespa simillima xanthoptera ) that usually waits at the entrance of their hive. Even though the hornets are many times bigger than the bees, bees numbers make the difference. These bees are adapted to survive temperatures above 46 °C (115 °F) but the hornet is not. Thus, bees are able to kill their attacker by making a ball around the hornet and then increasing their body temperature above 46 °C (115 °F). [15]

Anopheles mosquitoes, vectors of Malaria, thermoregulate each time they take a blood meal on a warm-blooded animal. During blood ingestion, they emit a droplet composed of urine and fresh blood that they keep attached to their anus. The liquid of the drop evaporates dissipating the excess of heat in their bodies consequence of the rapid ingestion of relatively high amounts of blood much warmer than the insect itself. This evaporative cooling mechanism helps them to avoid the thermal stress associated to their haematophagous way of life. [16]

The Grayling butterfly ( Hipparchia semele ) engages in thermoregulation as well. The species prefers to live in open habitats with easy access to the sun, and can be seen orienting its body to maximize exposure to the sun. At lower temperatures, the grayling can be observed exposing as much of its body as possible to the sun, whereas at higher temperatures, it exposes as little of its body as possible. This behavior is often used by male butterflies defending their territory, as this thermoregulatory behavior allows them to maximize their flight efficiency. [17]

The thermoregulatory properties of dark coloration are important for mate searching by Phymata americana males. [18] In cool climates, darker coloration allows males to reach warmer temperatures faster, which increases locomotor ability and decreases mate search time. [18]

See also

Related Research Articles

<span class="mw-page-title-main">Warm-blooded</span> Animal species that can maintain a body temperature higher than their environment

Warm-blooded is an informal term referring to animal species whose bodies maintain a temperature higher than that of their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. Other species have various degrees of thermoregulation.

<span class="mw-page-title-main">Bumblebee</span> Genus of insect

A bumblebee is any of over 250 species in the genus Bombus, part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related genera are known from fossils. They are found primarily in higher altitudes or latitudes in the Northern Hemisphere, although they are also found in South America, where a few lowland tropical species have been identified. European bumblebees have also been introduced to New Zealand and Tasmania. Female bumblebees can sting repeatedly, but generally ignore humans and other animals.

<i>Helicoverpa zea</i> Species of moth

Helicoverpa zea, commonly known as the corn earworm, is a species in the family Noctuidae. The larva of the moth Helicoverpa zea is a major agricultural pest. Since it is polyphagous during the larval stage, the species has been given many different common names, including the cotton bollworm and the tomato fruitworm. It also consumes a wide variety of other crops.

<span class="mw-page-title-main">Endotherm</span> Organism that maintains body temperature largely by heat from internal bodily functions

An endotherm is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions instead of relying almost purely on ambient heat. Such internally generated heat is mainly an incidental product of the animal's routine metabolism, but under conditions of excessive cold or low activity an endotherm might apply special mechanisms adapted specifically to heat production. Examples include special-function muscular exertion such as shivering, and uncoupled oxidative metabolism, such as within brown adipose tissue.

<span class="mw-page-title-main">Thermoregulation</span> Ability of an organism to keep its body temperature within certain boundaries

Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature as its own body temperature, thus avoiding the need for internal thermoregulation. The internal thermoregulation process is one aspect of homeostasis: a state of dynamic stability in an organism's internal conditions, maintained far from thermal equilibrium with its environment. If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as hyperthermia occurs. Humans may also experience lethal hyperthermia when the wet bulb temperature is sustained above 35 °C (95 °F) for six hours. Work in 2022 established by experiment that a wet-bulb temperature exceeding 30.55°C caused uncompensable heat stress in young, healthy adult humans. The opposite condition, when body temperature decreases below normal levels, is known as hypothermia. It results when the homeostatic control mechanisms of heat within the body malfunction, causing the body to lose heat faster than producing it. Normal body temperature is around 37°C(98.6°F), and hypothermia sets in when the core body temperature gets lower than 35 °C (95 °F). Usually caused by prolonged exposure to cold temperatures, hypothermia is usually treated by methods that attempt to raise the body temperature back to a normal range. It was not until the introduction of thermometers that any exact data on the temperature of animals could be obtained. It was then found that local differences were present, since heat production and heat loss vary considerably in different parts of the body, although the circulation of the blood tends to bring about a mean temperature of the internal parts. Hence it is important to identify the parts of the body that most closely reflect the temperature of the internal organs. Also, for such results to be comparable, the measurements must be conducted under comparable conditions. The rectum has traditionally been considered to reflect most accurately the temperature of internal parts, or in some cases of sex or species, the vagina, uterus or bladder.

<span class="mw-page-title-main">Ectotherm</span> Organism where internal heating sources are small or negligible

An ectotherm, more commonly referred to as a "cold-bloodedanimal", is an animal in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature. Such organisms rely on environmental heat sources, which permit them to operate at very economical metabolic rates.

<span class="mw-page-title-main">Heterothermy</span> Metabolic system

Heterothermy or heterothermia is a physiological term for animals that vary between self-regulating their body temperature, and allowing the surrounding environment to affect it. In other words, they exhibit characteristics of both poikilothermy and homeothermy.

<span class="mw-page-title-main">Grayling (butterfly)</span> Species of butterfly

The grayling or rock grayling is a species in the brush-footed butterfly family Nymphalidae. Although found all over Europe, the grayling mostly inhabits coastal areas, with inland populations declining significantly in recent years. The grayling lives in dry and warm habitats with easy access to the sun, which helps them with body temperature regulation.

<span class="mw-page-title-main">Forest tent caterpillar moth</span> Species of insect

The forest tent caterpillar moth is a moth found throughout North America, especially in the eastern regions. Unlike related tent caterpillar species, the larvae of forest tent caterpillars do not make tents, but rather, weave a silky sheet where they lie together during molting. They also lay down strands of silk as they move over branches and travel as groups along these pheromone-containing silk trails. The caterpillars are social, traveling together to feed and massing as a group at rest. Group behavior diminishes as the caterpillars increase in size, so that by the fifth instar (molt) the caterpillars are feeding and resting independently.

The obelisk posture is a handstand-like position that some dragonflies and damselflies assume to prevent overheating on sunny days. The abdomen is raised until its tip points at the sun, minimizing the surface area exposed to solar radiation. When the sun is close to directly overhead, the vertical alignment of the insect's body suggests an obelisk.

<span class="mw-page-title-main">East African lowland honey bee</span> Subspecies of honey bee native to Africa

The East African lowland honey bee is a subspecies of the western honey bee. It is native to central, southern and eastern Africa, though at the southern extreme it is replaced by the Cape honey bee. This subspecies has been determined to constitute one part of the ancestry of the Africanized bees spreading through North and South America.

<i>Spodoptera littoralis</i> Species of moth

Spodoptera littoralis, also referred to as the African cotton leafworm or Egyptian cotton leafworm or Mediterranean brocade, is a species of moth in the family Noctuidae. S. littoralis is found widely in Africa, Mediterranean Europe and Middle Eastern countries. It is a highly polyphagous organism that is a pest of many cultivated plants and crops. As a result, this species was assigned the label of A2 quarantine pest by the EPPO and was cautioned as a highly invasive species in the United States. The devastating impacts caused by these pests have led to the development of both biological and chemical control methods. This moth is often confused with Spodoptera litura.

<span class="mw-page-title-main">Western honey bee</span> European honey bee

The western honey bee or European honey bee is the most common of the 7–12 species of honey bees worldwide. The genus name Apis is Latin for "bee", and mellifera is the Latin for "honey-bearing" or "honey carrying", referring to the species' production of honey.

<i>Mythimna unipuncta</i> Species of moth

Mythimna unipuncta, the true armyworm moth, white-speck moth, common armyworm, or rice armyworm, is a species of moth in the family Noctuidae. The species was first described by Adrian Hardy Haworth in 1809. Mythimna unipuncta occurs in most of North America south of the Arctic, as well as parts of South America, Europe, Africa, and Asia. Although thought to be Neotropical in origin, it has been introduced elsewhere, and is often regarded as an agricultural pest. They are known as armyworms because the caterpillars move in lines as a massive group, like an army, from field to field, damaging crops.

<i>Galleria mellonella</i> Species of moth

Galleria mellonella, the greater wax moth or honeycomb moth, is a moth of the family Pyralidae. G. mellonella is found throughout the world. It is one of two species of wax moths, with the other being the lesser wax moth. G. mellonella eggs are laid in the spring, and they have four life stages. Males are able to generate ultrasonic sound pulses, which, along with pheromones, are used in mating. The larvae of G. mellonella are also often used as a model organism in research.

<i>Xylocopa sonorina</i> Species of bee

Xylocopa sonorina, the valley carpenter bee or Hawaiian carpenter bee, is a species of carpenter bee found from western Texas to northern California, and the eastern Pacific islands. Females are black while males are golden-brown with green eyes.

<span class="mw-page-title-main">Kleptothermy</span> Form of thermoregulation in which an animal shares in the heat production of another

In biology, kleptothermy is any form of thermoregulation by which an animal shares in the metabolic thermogenesis of another animal. It may or may not be reciprocal, and occurs in both endotherms and ectotherms. One of its forms is huddling. However, kleptothermy can happen between different species that share the same habitat, and can also happen in pre-hatching life where embryos are able to detect thermal changes in the environment.

<i>Bombus vosnesenskii</i> Species of bee

Bombus vosnesenskii, the yellow-faced bumblebee, is a species of bumblebee native to the west coast of North America, where it is distributed from British Columbia to Baja California. It is the most abundant species of bee in this range, and can be found in both urban and agricultural areas. Additionally, B. vosnesenskii is utilized as an important pollinator in commercial agriculture, especially for greenhouse tomatoes. Though the species is not currently experiencing population decline, urbanization has affected its nesting densities, and early emergence of the B. vosnesenskii has been implicated in the increasing lack of bee diversity on the West coast.

<i>Taeniopoda eques</i> Species of grasshopper

Taeniopoda eques, the western horse lubber grasshopper, is a relatively large grasshopper species of the family Romaleidae found in arid and semi-arid parts of southwestern United States to central and southwestern Mexico. Most populations are identifiable by their shiny black bodies with contrasting yellow markings, but some adults are mostly yellowish, orangish or greenish. The species is unique in using its black coloration to thermoregulate and in being chemically defended. The aposematic coloration warns vertebrate predators of its unpalatability and allows the grasshopper to roost conspicuously upon shrubs.

<i>Bombus terricola</i> Species of bee

Bombus terricola, the yellow-banded bumblebee, is a species of bee in the genus Bombus. It is native to southern Canada and the east and midwest of the United States. It possesses complex behavioral traits, such as the ability to adapt to a queenless nest, choose which flower to visit, and regulate its temperature to fly during cold weather. It was at one time a common species, but has declined in numbers since the late 1990s, likely due to urban development and parasite infection. It is a good pollinator of wild flowers and crops such as alfalfa, potatoes, raspberries, and cranberries.

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Further reading