Insect thermoregulation
Insect thermoregulation is the process whereby insects maintain body temperatures within certain boundaries.
In-flight thermoregulation
Pre-flight thermoregulation
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
Another example of thermoregulation is that of heat being used as a defensive mechanism. The Japanese honeybee (
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
- Thermoregulation
- Entomology
- Ethnoentomology
- Flying and gliding animals
References
Further reading
- SP Roberts, JF Harrison (1999), "Mechanisms of thermal stability during flight in the honeybee apis mellifera", J Exp Biol, 202 (11):1523-33
- Cheng-Chia Tsai, Richard A. Childers, Norman Nan Shi, Crystal Ren, Julianne N. Pelaez, Gary D. Bernard, Naomi E. Pierce & Nanfang Yu (2020), "Physical and behavioral adaptations to prevent overheating of the living wings of butterflies", Nature Communications, 11 (551)