Respiratory system of insects. How do aquatic insects breathe? How do insects breathe?

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Respiration process in terrestrial insects

In the simplest cases

In arid biotopes

Video demonstrates the breathing process of a praying mantis

The operation of the closure devices reduces water loss during breathing. (video)

During respiratory movements, they move away from each other and come closer, and in Hymenoptera they also make telescopic movements, that is, the rings retract into each other during “exhalations” and straighten out during “inhalations.” At the same time, the active respiratory movement, which is caused by muscle contraction, is precisely “exhalation” and not “inhalation,” unlike in humans and animals, for whom the opposite is true.

The rhythm of respiratory movements can be different and depends on many factors, for example, on temperature: in the Melanoplus filly, at 27 degrees, 25.6 respiratory movements are carried out per minute, and at 9 degrees there are only 9. Before, many increase their breathing, and during it inhalations and exhalations often stop. A honeybee has 40 respiratory movements at rest, and 120 when working.

Some researchers write that, despite the presence of respiratory movements, insects do not have typical inhalations and exhalations. We can agree with this, taking into account the characteristics of a number of taxa. Thus, in locusts, air enters the body through the front pairs and leaves through the rear pairs, which creates differences from “normal” breathing. By the way, in the same insect, with an increased carbon dioxide content, the air in can begin to move in the opposite direction: drawn in through the abdominal and exited through.

How do aquatic insects breathe?

In insects that live in water, respiration occurs in two ways. It depends on what structure they have.

Many of the aquatic organisms have a closed environment in which they do not function. It is closed and there are no “exits” to the outside. Breathing is carried out using - outgrowths of the body into which they enter and branch abundantly. Thin tracheoles come so close to the surface that oxygen begins to diffuse through them. This allows some insects living in water (including caddis flies, stoneflies, mayflies, dragonflies) to carry out gas exchange. During their transition to terrestrial existence (transformation into) they are reduced, and from closed they turn into open.

In other cases, the respiration of aquatic insects is carried out by atmospheric air. Such insects have an open. They take in air through, floating to the surface, and then sink under water until it is used up. In this regard, they have two structural features:

Other features are also possible. For example, in the swimming beetle they are located at the rear end of the body. When she needs to “take a breath,” she swims to the surface, takes vertical position“upside down” and exposes the part where the .

The breathing of adult swimmers is interesting. They have developed, lateral sides that bend downward and inward, toward the body. As a result, when floating to the surface with the elytra folded, the beetle captures an air bubble, which enters the sub-elite space. They open there too. This is how the swimmer renews its oxygen reserves. The swimmer of the genus Dyliscus can stay under water for 8 minutes between surfacings, Hyphidrus for about 14 minutes, and Hydroporus for up to half an hour. After the first frost, the beetles also remain viable under the ice. They find air bubbles underwater and swim over them so as to “take” them under.

In the water lover, air is stored between the hairs located on the ventral part of the body. They are not wetted, so a supply of air is formed between them. When the insect swims underwater, its ventral part appears silvery due to the air cushion.

In aquatic insects that breathe atmospheric air, the small reserves of oxygen that they capture from the surface should be consumed very quickly, but this does not happen. Why? The fact is that oxygen diffuses from water into air bubbles, and carbon dioxide partially escapes from them into the water. Thus, by taking air under water, the insect receives a supply of oxygen, which is replenished by itself for some time. The process is highly temperature dependent. For example, the Plea bug can live in boiled water for 5-6 hours at warm temperatures and 3 days at cold temperatures.

In all of these cases, skin respiration occurs. Insects breathe over the entire surface of the body (the first instars

). On the sides of the body there are up to 10 pairs, sometimes fewer, of spiracles, or stigmas: they lie on the meso- and metathorax and on 8 abdominal segments.

Stigmas are often equipped with special closing devices and each lead into a short transverse canal, and all transverse canals are connected to each other by a pair (or more) of the main longitudinal tracheal trunks. Thinner tracheas originate from the trunks, branching repeatedly, and entangling all the organs with their branches. Each trachea ends with a terminal cell with radially diverging processes, penetrated by the terminal tubules of the trachea (Fig. 341). The terminal branches of this cell (tracheoles) even penetrate into individual cells of the body.

Sometimes the trachea forms local expansions, or air sacs, which serve in terrestrial insects to improve air ventilation in the tracheal system, and in aquatic insects, probably as reservoirs that increase the supply of air in the animal’s body.

Tracheas appear in insect embryos in the form of deep invaginations of the ectoderm; like other ectodermal formations, they are lined with a cuticle (Fig. 341). In the surface layer of the latter, a spiral thickening is formed, which gives the trachea elasticity and prevents the walls from collapsing.

In the simplest cases, the entry of oxygen into the tracheal system and the removal of carbon dioxide from it occurs by diffusion through constantly open stigmas. This is observed, however, only in inactive insects living in conditions of high humidity.

Activation of behavior and the transition to living in arid biotopes significantly complicate the breathing mechanism. The body's increasing need for oxygen is ensured by the appearance of special respiratory movements, consisting of relaxation and contraction of the abdomen. In this case, the tracheal sacs and main tracheal trunks are ventilated. The formation of closure devices on the stigmas reduces water loss during respiration. Since the rate of diffusion of water vapor is lower than that of oxygen, when the stigmas are opened for a short time, oxygen has time to penetrate into the tracheal system, and water losses are minimal.

In many insect larvae living in water (for example, dragonflies, mayflies, etc.), the tracheal system is closed, that is, there are no stigmas, while the tracheal network itself is present. In such forms, oxygen diffuses from the water through the tracheal gills, lamellar or bushy, thin-walled outgrowths of the body, penetrated by a rich network of tracheae (Fig. 342). Most often, the tracheal gills sit on the sides of part of the abdominal segments (mayfly larvae). Oxygen enters through the thin covers of the gills, enters the trachea and is then distributed throughout the body.

During the transformation of gill-breathing larvae into an adult insect living on land, the gills disappear, the stigmata open and the tracheal system changes from closed to open.

Important physiological feature respiratory system insects is as follows. Typically, oxygen is perceived by an animal in certain parts of its body and from there it is distributed by blood throughout the body. In insects, air tubes permeate the entire body and deliver oxygen directly to the places of its consumption, that is, to tissues and cells, as if replacing blood vessels.

Structure of the tracheal system. Insects breathe through a system of tracheas distributed throughout the body, less often through the surface of the skin. The tracheae are represented by hollow tubes lined with chitin in the form of spiral thickenings that prevent the trachea from collapsing during movement and bending of the body. The tracheae branch into tiny capillaries - tracheoles with a diameter of less than 1 micron, which deliver air oxygen directly to the tissues and cells of the body.

Breath. The entry of air into the tracheal system most often occurs actively, with the help of respiratory movements. In this case, certain spiracles open or close, inhaling or exhaling. The rhythm of respiratory movements depends on the type of insect, its condition and external conditions. Thus, a honey bee at rest makes about 40 respiratory movements per minute, and when moving - up to 120; in some locusts, an increase in their number from 6 to 26 or more occurs with an increase in environmental temperature from 0 °C to 27 °C and above.

In many species of insects, air is inhaled through the pectoral spiracles and exhaled through the abdominal spiracles. The rhythm of the spiracles is associated with breathing movements abdomen; with an increase and decrease in air pressure caused by these movements, some spiracles open outward, others open into the insect's body. However, under the influence of large doses of carbon dioxide, various poisons, and sometimes for no apparent reason, air circulation can change, that is, it begins to enter through the abdominal spiracles and exit through the thoracic ones. In addition, with an increase in carbon dioxide content and a lack of oxygen in the environment, the spiracles remain open for a longer time, and therefore fumigation of the premises against pests will be more effective.

Respiration is an oxidative process that occurs through the consumption of oxygen and the release of carbon dioxide. The oxidation process occurs with the participation of oxidative enzymes - oxidases and is accompanied by the gradual breakdown of molecules of consumable compounds - carbohydrates, fats, proteins - and the release of energy. The breakdown of these compounds ultimately ends with the formation of carbon dioxide and water, and for proteins, also the appearance of breakdown products that are bound into compounds that are safer for the body, such as urea and its salts.

Thus, breathing is accompanied by gas exchange. The gas exchange process is characterized by the respiratory coefficient (RC), which represents the ratio of released carbon dioxide to the total amount of absorbed oxygen. Based on this indicator, one can judge which substances are currently used as a source of energy. When oxidizing carbohydrates, DC = 1, when using less oxidized fat compounds, DC decreases to 0.7, and proteins - to 0.77-0.82. For example, when cockroaches are starving, the DC decreases to 0.65-0.85, which corresponds to the predominant consumption of previously stored fats.

Other forms of breathing. Respiration of aquatic insects occurs both due to atmospheric air and through the use of air dissolved in water. Thus, swimming beetles, living in water, breathe using atmospheric air stored under the elytra at the end of the abdomen, and from time to time rise to the surface to replenish its reserves. Beetles from the genus irisfish are mined atmospheric air from the air vessels of aquatic plants.

When using air dissolved in water, insects breathe using gills. The gills are represented by external branched or lamellar formations located in the place of the missing spiracles. They are developed in the larvae of mayflies, dragonflies, caddisflies, and some dipterans. In the larvae of heteroptera dragonflies, the gills are rectal, i.e. internal organs and are located in the rectum.

Body temperature. Insects are animals with variable body temperatures. It depends on the intensity of heat generation processes and its release. The sources of heat formation in insects are, on the one hand, metabolic processes in the body, accompanied by the release of thermal energy, and the radiant energy of the sun or the air heated by it, on the other.

According to I.D. Strelnikov, the body temperature of insects that are at rest and not exposed to sun irradiation is approximately equal to the temperature environment. Due to the fact that the temperature optimum for many species fluctuates around 20...35 °C, insects can regulate body temperature within certain limits by changing muscle activity (movement, flight) or moving to warmer or cooler areas, sometimes beyond posture change account. Known value evaporation of water from the surface of the skin and ventilation of the trachea, especially with the help of air sacs, can help regulate body temperature.