What are the sense organs in insects? The structure of the body of an insect - the sense organs and the nervous system of insects What do you know about the sense organs of insects
The sense organs are inseparable from the central nervous system of the body. If the latter has a control function, coordinating the physiological processes and behavioral reactions of the body, then the sense organs through their signals connect the central nervous system both with the external world and with the internal environment of the body. Sensory or receptor cells, scattered throughout the body or combined into complex receptor organs, serve as a kind of "windows" to the outside world and internal environment organism. The information that enters the central nervous system through them is extremely diverse and, as we will see below, is absolutely necessary for the organization of expedient behavior, as well as for the biologically justified and coordinated functioning of the physiological systems of the body.
The fulfillment of all three indispensable vital tasks of the organism: nutrition, reproduction and resettlement, which ensure the preservation of the species, is possible only thanks to continuous control by various sensory organs. The receptors, together with their brain centers, collectively called analyzers, not only single out certain objects and phenomena from the background, i.e. answer the question "what?", but also establish the position of the object in space, i.e. respond to the question is "where?".
Let us consider, using examples, how the sense organs make it possible to fulfill the above life tasks and what questions a researcher has when observing the sensory behavior of an insect.
reproduction. The most characteristic form of behavior associated with reproduction is the search for a sexual partner. The involvement of the sense organs in the maintenance of sexual behavior is quite obvious, and, perhaps, it is in this area that the amazing possibilities inherent in the structure of the receptor systems of insects are manifested. The main role in the search and identification of a sexual partner in most insects is played by the sense of smell, which is narrowly tuned to the perception of a sexual attractant. Among the innumerable multitude of odors, the male unmistakably singles out one, precisely the one that belongs to the female of his species, although it can also react to the odors of related species. The sexual attractant of the female excites the male's chemoreceptors at an insignificant concentration of molecules in the air, which allows him to find the female from a distance (in the record case) up to 12 km. The male, in turn, often has "charm" organs, the odorous secret of which - an aphrodisiac - predisposes the female to copulation. In other words, both sexual partners exchange species-specific odorous signals, which ensures the reliability of their meeting.
It has recently been shown on the oak leafworm Tortrix vlridana that the sex pheromone enters the body of the female from the larval food plant and is determined by the chemistry of the latter. Therefore, females reared on diet A do not attract males reared on diet B. This circumstance leads to reproductive isolation of populations and may be the cause of the emergence of temporary (reversible) intraspecific forms.
In diurnal species and in luminous insects, the role of vision in sexual behavior is especially significant. The coloration of the wings and the whole body, the nature of the flight, and some other visual signs serve for diurnal butterflies, dragonflies, many flies and other insects as specific signals of the male and female, which are easily caught by their compound eyes. Sometimes these features are so specific to insects that we can judge their existence only with the help of special instruments. For example, we do not see with the naked eye the difference in the reflection of ultraviolet rays by the wings, which in some butterflies is an effective secondary sex trait. In a number of cases, it was possible to identify special color detectors in the visual system of insects, narrowly tuned to the perception of the color of the sexual partner. Optical signaling in fireflies is well known, but not everyone suspects how complex it is organized. Each species has its own identification lights - luminous spots that differ in configuration and temporal parameters. To the flash of the species-specific signal of the male, his chosen one responds after a strictly defined time interval with a calling glow. The strict species specificity of the set of signals and responses ensures reliable communication and at the same time serves as an ethological barrier if several species live together.
It is surprising with its complexity in sexual behavior and acoustic signaling. Against the background of various noises (even very loud ones), grasshoppers, crickets and some other insects, tens of meters away, emit the invocative song of the sexual partner and find the direction of the sound source. In addition to the call song, there are other signals: copulatory, threatening and territorial. The ability of the auditory analyzer to fine-tune species-specific, in particular, gives rise to the emergence of local dialects of territorial songs, well studied in the locust British Isles.
resettlement. Settlement requires, first of all, a reliable orientation in space, otherwise the animal will move chaotically and will not be able to leave the original territory. Dispersal associated with orientation can be either active - scattering, spreading, or passive - transport by wind or water. During active dispersal, insects are guided mainly visually by ground landmarks and a celestial compass in the form of the sun, the polarization of the light of the blue sky and the moon. In this case, targeting becomes possible due to the mechanism of one of the taxises, which allows, based on signals from receptors, to keep the locomotor axis in the chosen direction. The "navigation art" of insects, capable of correcting the chosen course for the daily shift of celestial landmarks, is almost as good as the art of birds using a celestial compass. It is possible that insects, like birds, also orient themselves by magnetic field Earth. In passive transport, such as by wind, insects choose a certain posture that promotes directional transport of the body through the air, based on information from wind-sensing hairs and other receptors.
All of these forms of activity are associated either with locomotion or with maintaining a certain position of the body in space, as well as individual parts of the body relative to each other. Both are possible only on the basis of information coming from special sensors. These primarily include various mechanoreceptors that are sensitive to stretching, compression or torque - stimuli applied to the cuticle, connective tissue and muscles as a result of either external influence, or internal effort, or only the weight of a given part of the body. Mechanoreceptor signals provide posture control, coordination of movements of body parts during running, swimming, cocoon curling, copulation, etc., and also signal the breaking of contact with the substrate, the direction and speed of body displacement during movement.
The role of sensory signals in the implementation of the motor reactions of insects is given a good idea by the analysis of the throw of the mantis Mantis religiosa on prey. The praying mantis, turning its head, tracks the prey visually and can grab it even when it is on the side of its longitudinal axis. Therefore, the center controlling the throw must have information both about the direction to the prey relative to the head of the praying mantis, and about the position of the head relative to the prothorax with its prehensile legs. Information of the first kind is given by the eyes, information of the second kind is given by mechanoreceptors - two pairs of so-called hair plates in the cervical region. If you cut the nerves from all the cervical hair plates (deafferent the control center), then the reliability of the throw drops to 20-30% against 85% in the norm. With deafferentation of only one left side, misses become more frequent, and the praying mantis tends to direct the throw to the right of the target. Signals coming only from the right cervical plates are interpreted by the control center as a turn of the head to the right.
Afferent control of walking is carried out by an exceptionally large set of mechanoreceptors: in particular, certain receptors of the paw, lower leg, and thigh are responsible for stimulating certain leg muscles of levators and depressors. Some of them, such as the bell-shaped sensilla, are positioned so that they are excited by the tension forces arising in the leg when the insect is normally standing. Therefore, if the mechanoreceptors of the leg are destroyed, then the mechanical aspect of walking is disturbed in the insect: gait, speed, etc. The walking posture is often regulated by feedback with hair plates that control the angle between the coxa and the trochanter (together with the thigh). The stick insect Caraussius morosus normally freely holds the body above the ground. The gap between them is maintained even when the insect carries a load four times heavier than the body. If the hair plates are damaged, then the stick insect begins to touch the substrate even under the weight of its own body.
Of all the forms of locomotion, flight is the most sensory demanding. Afferent signals not only cause flight, they are also necessary for its maintenance and regulation. The so-called tarsal reflex is well known: detachment of the legs from the support in many insects causes flight or swimming movements (for example, in water bugs - belostomatids), which immediately stop when contact with the substrate is resumed. Several types of mechanoreceptor sensilla in the legs serve as sensors for the tarsal reflex. Flight-supporting receptors include wind-sensing hairs on the head and wings. Their phase-tonic signals depend on the speed and direction of the air flow and can not only maintain and regulate flight, but also launch it. In bees, flies, and aphids, Johnston's antenna organ is also involved in automatic flight stabilization. Its signals, along with other sensors, regulate the operation of the wings: the greater the air pressure on the antenna bundle, the smaller the amplitude of the ipsilateral wing flaps. It is easy to imagine that on the basis of such a negative feedback loop, a straight flight direction is automatically maintained.
Receptors are involved in the regulation of not only the locomotor system, but also almost all other physiological systems and organs. Their participation in controlling the process of digestion, for example, is very conspicuous in blood-sucking mosquitoes. Female Anopheles mosquitoes feed not only on the blood of vertebrates, but also drink the so-called "free fluids": juice protruding from plants, dew, etc. In this case, only blood enters directly into the intestines, while other fluids are initially stored in the blind branch of the esophagus - in bulky food tank. But if in the experiment the mosquito drinks an openly lying drop of blood, without puncturing the cover of the victim, then the blood does not enter the intestines, but also into the food reservoir, and the insect soon dies. The fact is that the direction of the current of the liquid absorbed by the insect is controlled by receptors located on the proboscis and in the pharynx.
An example of receptor activation of the endocrine glands is the dependence of the molting of the blood-sucking bug Rhodnius on the amount of blood drunk: the larva molts only after drinking a certain portion of blood, and at a time. If the larva receives the same portion of blood in several doses, with breaks between separate acts of bloodsucking, then it does not molt. The experiments of the prominent English entomophysiologist W. Wigglesworth showed that the relationship between molting and bloodsucking is quite complex. Molting occurs under the action of the hormone ecdysone secreted by the prothoracic gland, which is stimulated by signals from neurosecretory brain cells. The brain center, in turn, is activated by signals from certain receptors, including stretch receptors, which are located in the walls of the bug's abdomen. These receptors work only when the intestine expands to a certain threshold volume, which occurs when a certain portion of blood enters it. In the same way, signals about stretching of the rectum, for example, trigger the act of defecation, signals about stretching of the ducts of the gonads of the female inform the central nervous system about the readiness of the body for oviposition, etc. The examples given convincingly show that coordinated work internal organs depends on information coming from interoreceptors.
There is another reason that contributed to the rapid development of the physiology of the sense organs of insects and animals in general - this is the bionic aspect of the problem of reception. Animal receptors are usually superior in many respects to similar-purpose sensors currently being designed by humans. Therefore, the desire to study this or that living system is understandable in order to create a technical device similar in principle of operation. The physiology of the sense organs, in comparison with most other biological disciplines, has moved far ahead as a result of the inclusion in its arsenal of approaches introduced on the path of bionic search by physicists, cybernetics, and mathematicians. For bionics, only qualitative characteristics are not enough, but quantitative parameters of a living system, translated into the language of mathematics, are necessary.
More specifically, engineers are interested in the sense organs of insects as potential prototypes. technical devices with exceptionally high sensitivity, noise immunity, redundant design, combined with miniaturization and low energy consumption for operation. The sensitivity of insect receptor cells is practically brought to the physical limit. So, in order to excite the olfactory cell on the antenna of the male silkworm, tuned to the perception of the female sexual attractant, contact with one molecule of this substance is enough. The visual cell of the compound eye can be excited by a single photon. The mechanoreceptor cell of the so-called popliteal organ detects vibrations of the substrate, the amplitude of which is less than the diameter of a hydrogen atom. At the same time, the receptors differ from the known technical sensors of information by their amazing noise immunity. We have already noted that the grasshopper distinguishes (recognizes) a species-specific song against the background of the most diverse sounds. A bee from afar visually recognizes a flower known to her among many other objects similar in size, color and shape. The redundancy in the design of living systems is manifested in the fact that the destruction of a part of an organ does not put it out of action, and in insects this property is combined with the extreme miniaturization of all organs.
In all receptor systems, without exception, bionics are especially striving to decipher highly efficient biological methods for separating a signal from noise. Along with this, in the olfactory analyzer the main object of search is methods for organizing exceptionally high and selective sensitivity to odors, in the auditory analyzer - methods for finding the sound source and identifying its signals, in the visual analyzer - mechanisms for analyzing the polarization of light and the perception of rays invisible to humans.
The achievements of sensory bionics, as far as can be judged from the available publications*, are still more modest than the success achieved by sensory physiology itself, enriched with a physical approach borrowed from bionics. As an example of success, let's name the creation of a device for measuring the speed of aircraft relative to the Earth, working on the principle of perception of movement by the compound eye, discovered in the weevil Chlorophanus. It has been repeatedly reported on the creation of acoustic devices that attract (and destroy) blood-sucking mosquitoes, and ultrasonic emitters that imitate the cry of bats and scare away harmful moths that hear these sounds. In the fight against gypsy moth and related species successfully use traps with a sexual attractant (for example, synthetic disparlur). Improved light traps emitting ultraviolet rays, especially attractive to nocturnal insects.
* (It is known that bionic research abroad is widely funded by the military department and many of them have a corresponding focus that is not subject to wide publicity.)
Both bionics and biologists of various specialties are of great interest to the problem of pattern recognition associated with the study of receptors, with a brief summary of which we will conclude our review of the role of the sense organs in the life of insects.
The search for this or that object is always based on the distinction (discrimination) of external stimuli and their modalities, for which the receptors are entirely responsible, since they are at the "entrance" of the organism. But a purposeful choice is possible only if the receptor signals from the object coincide with its description or features embedded in the central nervous system of the body. Therefore, the choice of an object is determined not only by sensory information coming from outside, but also by that contained in the genetic or individual memory of the organism. The choice is preceded by the identification of the object as such, by comparison with the standard idea of it, which already exists in the central nervous system.
In this regard, a fundamental question arises: in what form is the description of objects stored in the memory of insects - in the form of specific features of each of them individually or a generalized representation? The following example will clarify our idea. When a bee unmistakably finds its hive by color (beekeepers have long noticed that color makes it easier to find, and therefore adjacent hives are painted in different colors), then to an inexperienced observer it may seem that the situation is quite simple. The bee, as you know, can distinguish colors, so she identifies her hive by color. But in reality, she recognizes the hive as such, does not confuse it with other objects that are identically colored. The task for the bee can be made more difficult by placing an object on the hive that distorts the appearance of the hive. Formally, in the language of describing this situation by eye receptors, here the object is different, nevertheless, a trained bee and under these conditions recognizes it as a hive. This means that the bee keeps in memory the image of the hive - some generalized idea of it, which, as you can easily guess, can only arise as a result of personal experience, multiple return to the hive in different situations and selection in the process of forming the image of the main optical features of the hive.
The ability of the honey bee for visual generalization has recently been confirmed in special experiments in which the insect was trained on different objects, but belonging to the same class of objects reinforced (by food) according to one characteristic common to all of them, to which the class of unreinforced objects was opposed. Previously, this logical operation was considered the privilege of exclusively higher animals with a voluminous brain, in whose behavior some researchers saw signs of "elementary reason".
The problem of pattern recognition turned out to be in the center of attention not only of biologists, but also of designers of "thinking" machines. The fact is that visual recognition in humans and animals is invariant to many transformations of a recognizable object. We recognize a familiar face from the front and in profile, in a photograph, from a contour drawing, and even in a caricature. Identification is preceded by the selection of some key features, and on their basis follows a logical operation of generalization and image formation. But what signs and how the brain generalizes them is far from always known, and this is the difficulty in creating algorithms and programs for computers, for example, reading texts typed in different fonts. Not all of the experiments required here are possible on humans, and some of them, especially with surgical intervention, are feasible only on animals. This explains the relevance of studying the complex forms of behavior of insects, in this case visual behavior of bees. The relatively small number of neurons in the retina and especially in the head ganglion makes bees, in comparison with higher vertebrates, a more accessible object for studying the peripheral and central mechanisms of generalization and pattern recognition.
Sense organs in insects
Zhdanova T. D.
Coming into contact with the varied and energetic activities of the insect world can be an amazing experience. It would seem that these creatures carelessly fly and swim, run and crawl, buzz and chirp, gnaw and carry. However, all this is not done aimlessly, but mainly with a certain intention, according to the innate program embedded in their body and the acquired life experience. For the perception of the surrounding world, orientation in it, the implementation of all expedient actions and life processes, animals are endowed with very complex systems, primarily nervous and sensory.
What do the nervous systems of vertebrates and invertebrates have in common?
The nervous system is a complex complex of structures and organs, consisting of nervous tissue, where the central section is the brain. The main structural and functional unit of the nervous system is a nerve cell with processes (in Greek, a nerve cell is a neuron).
The nervous system and the brain of insects provide: perception with the help of the senses of external and internal irritation (irritability, sensitivity); instant processing by the system of analyzers of incoming signals, preparation and implementation of an adequate response; storage in memory in an encoded form of hereditary and acquired information, as well as its instantaneous retrieval as needed; management of all organs and systems of the body for its functioning as a whole, balancing it with the environment; implementation of mental processes and higher nervous activity, expedient behavior.
The organization of the nervous system and brain of vertebrates and invertebrates is so different that at first glance it seems impossible to compare them. And at the same time, for the most diverse types of the nervous system, belonging, it would seem, to both completely “simple” and “complex” organisms, the same functions are characteristic.
The very tiny brain of a fly, bee, butterfly or other insect allows it to see and hear, touch and taste, move with great accuracy, and moreover, fly using an internal “map” over considerable distances, communicate with each other and even own its own “language”, learn and apply in non-standard situations logical thinking. So, the brain of an ant is much smaller than a pinhead, but this insect has long been considered a "sage". When compared not only with his microscopic brain, but also with the incomprehensible capabilities of a single nerve cell, a person should be ashamed of his most modern computers. And what can science say about this, for example, neurobiology, which studies the processes of birth, life and death of the brain? Was she able to unravel the mystery of the vital activity of the brain - this most complex and mysterious of the phenomena known to people?
The first neurobiological experience belongs to the ancient Roman physician Galen. Having cut the nerve fibers in a pig, with the help of which the brain controlled the muscles of the larynx, he deprived the animal of its voice - it immediately became numb. It was a millennium ago. But how far has science gone since then in its knowledge of the principle of the brain? It turns out that despite the enormous work of scientists, the principle of operation of even one nerve cell, the so-called "brick" from which the brain is built, is still not known to man. Neuroscientists understand a lot about how a neuron "eats" and "drinks"; how it receives the energy necessary for its life activity, digesting the necessary substances extracted from the environment in “biological boilers”; how then this neuron sends to its neighbors a wide variety of information in the form of signals, encrypted either in a certain series of electrical impulses, or in various combinations chemical substances. And then what? Here a nerve cell received a specific signal, and in its depths a unique activity began in collaboration with other cells that form the brain of an animal. There is a memorization of the incoming information, the extraction of the necessary information from the memory, decision-making, giving orders to the muscles and various organs, etc. How is everything going? Scientists don't know for sure yet. Well, since it is not clear how individual nerve cells and their complexes, then the principle of operation of the whole brain, even as small as that of an insect, is not clear.
The work of the sense organs and living "devices"
The vital activity of insects is accompanied by the processing of sound, olfactory, visual and other sensory information - spatial, geometric, quantitative. One of the many mysterious and interesting features insects is their ability to accurately assess the situation using their own "instruments". Our knowledge of these devices is limited, although they are widely used in nature. These are determinants of various physical fields, which allow predicting earthquakes, volcanic eruptions, floods, weather changes. This and the sense of time, counted by internal biological clock, and a sense of speed, and the ability to navigate and navigate, and much more.
The property of any organism (microorganisms, plants, fungi and animals) to perceive irritations emanating from external environment and from their own organs and tissues, is called sensitivity. Insects, like other animals with a specialized nervous system, have nerve cells with a high selectivity for various stimuli - receptors. They can be tactile (responsive to touch), temperature, light, chemical, vibrational, muscular-articular, etc. Thanks to their receptors, insects capture the whole variety of environmental factors - various vibrations (a wide range of sounds, radiation energy in the form of light and heat), mechanical pressure (for example, gravity) and other factors. Receptor cells are located in tissues either singly or assembled into systems with the formation of specialized sensory organs - sense organs.
All insects perfectly "understand" the indications of their sense organs. Some of them, like the organs of vision, hearing, smell, are remote and are able to perceive irritation at a distance. Others, like the organs of taste and touch, are contact and respond to exposure through direct contact.
Insects in the mass are endowed with excellent vision. Their complex compound eyes, to which simple eyes are sometimes added, serve to recognize various objects. Some insects are provided with color vision, suitable night vision devices. Interestingly, the eyes of insects are the only organ that other animals have the likeness of. At the same time, the organs of hearing, smell, taste and touch do not have such a similarity, but, nevertheless, insects perfectly perceive smells and sounds, navigate in space, capture and emit ultrasonic waves. Delicate sense of smell and taste allow them to find food. A variety of glands of insects secrete substances to attract brothers, sexual partners, scare off rivals and enemies, and a highly sensitive sense of smell is able to detect the smell of these substances even for several kilometers.
Many in their ideas associate the sense organs of insects with the head. But it turns out that the structures responsible for collecting information about environment, are found in insects in various parts of the body. They can determine the temperature of objects and taste food with their feet, detect the presence of light with their backs, hear with their knees, whiskers, tail appendages, body hairs, etc.
The sense organs of insects are part of sensory systems - analyzers that penetrate the network of almost the entire organism. They receive many different external and internal signals from the receptors of their sense organs, analyze them, form and transmit "instructions" to various organs for the implementation of appropriate actions. The sense organs mainly make up the receptor section, which is located on the periphery (ends) of the analyzers. And the conductive department is formed by central neurons and pathways from receptors. The brain has certain areas for processing information coming from the senses. They constitute the central, “brain”, part of the analyzer. Thanks to such a complex and expedient system, for example, a visual analyzer, an accurate calculation and control of the organs of movement of an insect is carried out.
Extensive knowledge has been accumulated about the amazing capabilities of the sensory systems of insects, but the volume of the book allows us to cite only a few of them.
organs of vision
Eyes and the entire most complex visual system are an amazing gift, thanks to which animals are able to receive basic information about the world around them, quickly recognize various objects and evaluate the situation that has arisen. Vision is necessary for insects when searching for food to avoid predators, to explore objects of interest or environment, to interact with other individuals in reproductive and social behavior, etc.
Insects are equipped with a variety of eyes. They can be complex, simple or additional eyes, as well as larval. The most complex are compound eyes, which consist of a large number ommatidia, which form hexagonal facets on the surface of the eye. Ommatidium is essentially a tiny visual apparatus, equipped with a miniature lens, a light guide system and light-sensitive elements. Each facet perceives only a small part of the object, and together they provide a mosaic image of the entire object. Compound eyes, characteristic of most adult insects, are located on the sides of the head. In some insects, for example, a hunter dragonfly, which quickly reacts to the movement of prey, the eyes occupy half of the head. Each of her eyes is built from 28,000 facets. For comparison, butterflies have 17,000 of them, and a housefly has 4,000. Eyes on the head of insects can be two or three on the forehead or crown, and less often on its sides. Larval ocelli in beetles, butterflies, hymenoptera in adulthood are replaced by complex ones.
It is curious that insects cannot close their eyes during rest and therefore sleep with their eyes open.
It is the eyes that contribute to the quick reaction of an insect hunter, such as a praying mantis. By the way, this is the only insect that can turn around and look behind itself. Large eyes provide the praying mantis with binocular vision and allow you to accurately calculate the distance to the object of their attention. This ability, combined with the quick forward movement of the front legs towards the prey, make the mantid an excellent hunter.
And in yellow-footed beetles, running on the water, the eyes allow you to simultaneously see the prey both on the surface of the water and under it. To do this, the visual analyzers of the beetle have the ability to correct for the refractive index of water.
The perception and analysis of visual stimuli is carried out by the most complex system - the visual analyzer. For many insects, this is one of the main analyzers. Here, the primary sensitive cell is the photoreceptor. And the pathways (optic nerve) and other nerve cells located at different levels of the nervous system are connected with it. When perceiving light information, the sequence of events is as follows. The received signals (light quanta) are instantly encoded in the form of impulses and transmitted along the conducting paths to the central nervous system - to the "brain" center of the analyzer. There, these signals are immediately decoded (decoded) into the corresponding visual perception. For its recognition, standards of visual images and other necessary information are retrieved from memory. And then a command is sent to various organs for an adequate response of the individual to a change in the situation.
Where are the "ears" of insects located?
Most animals and humans hear with their ears, where sounds cause the eardrum to vibrate—strong or weak, slow or fast. Any change in vibration informs the body about the nature of the sound being heard. How do insects hear? In many cases, they are also peculiar “ears”, but in insects they are in places unusual for us: on the mustache - for example, in male mosquitoes, ants, butterflies; on the tail appendages - in the American cockroach. Crickets and grasshoppers hear with the shins of their front legs, and locusts hear with their stomachs. Some insects do not have "ears", that is, they do not have special organs of hearing. But they are able to perceive various fluctuations in the air environment, including sound vibrations and ultrasonic waves that are inaccessible to our ear. The sensitive organs of such insects are thin hairs or the smallest sensitive sticks. They are located in large numbers on different parts of the body and are associated with nerve cells. So, in hairy caterpillars, the “ears” are hairs, and in naked caterpillars, the whole skin covering body.
A sound wave is formed by alternating rarefaction and condensation of air, propagating in all directions from the sound source - any oscillating body. Sound waves are perceived and processed by the auditory analyzer - the most complex system of mechanical, receptor and nervous structures. These vibrations are converted by auditory receptors into nerve impulses that are transmitted along the auditory nerve to the central part of the analyzer. The result is the perception of sound and the analysis of its strength, height and character.
The auditory system of insects ensures their selective response to relatively high-frequency vibrations - they perceive the slightest tremors of the surface, air or water. For example, buzzing insects produce sound waves through rapid wing beats. Such a vibration of the air environment, for example, the squeak of mosquitoes, males perceive with their sensitive organs located on the antennae. Thus, they catch the air waves that accompany the flight of other mosquitoes and adequately respond to the received sound information. The auditory systems of insects are “tuned” to perceive relatively weak sounds, so loud sounds have a negative effect on them. For example, bumblebees, bees, flies of some species cannot rise into the air when they sound.
The varied but well-defined signal calls made by male crickets of each species play an important role in their reproductive behavior in courting and attracting females. The cricket is provided with a wonderful tool for communicating with a friend. When creating a gentle trill, he rubs the sharp side of one elytra against the surface of another. And for the perception of sound, the male and female have a particularly sensitive thin cuticular membrane, which plays the role of the eardrum. An interesting experiment was made when a chirring male was placed in front of a microphone, and a female was placed in another room near the telephone. When the microphone was turned on, the female, having heard the species-typical chirping of the male, rushed to the source of the sound, the telephone.
Organs for capturing and emitting ultrasonic waves
Moths are equipped with a device for detecting bats, which use ultrasonic waves for orientation and hunting. Predators perceive signals with a frequency of up to 100,000 hertz, and night butterflies and lacewings, which they hunt, up to 240,000 hertz. In the chest, for example, of the moth butterflies, there are special organs for acoustic analysis of ultrasonic signals. They make it possible to capture ultrasonic impulses of hunting kozhans at a distance of up to 30 m. When a butterfly perceives a signal from a predator locator, protective behavioral actions are activated. Hearing the ultrasonic calls of the night mouse at a relatively large distance, the butterfly abruptly changes the direction of flight, using a deceptive maneuver - "diving". At the same time, she begins to perform aerobatics - spirals and "dead loops" to get away from the chase. And if the predator is at a distance of less than 6 m, the butterfly folds its wings and falls to the ground. And the bat does not detect a motionless insect.
But the relationship between moths and bats has recently been found to be even more complex. So, butterflies of some species, having detected the signals of a bat, themselves begin to emit ultrasonic impulses in the form of clicks. Moreover, these impulses act on the predator in such a way that, as if frightened, it flies away. There is only speculation as to what causes bats to stop chasing the butterfly and "run away from the battlefield". It is likely that ultrasonic clicks are adaptive signals of insects, similar to those sent by the bat itself, only much stronger. Expecting to hear a faint reflected sound from his own signal, the pursuer hears a deafening roar - as if a supersonic aircraft breaks the sound barrier.
This begs the question why a bat is stunned not by its own ultrasonic signals, but by butterflies. It turns out that the bat is well protected from its own scream-impulse sent by the locator. Otherwise, such a powerful impulse, which is 2,000 times stronger than the received reflected sounds, can deafen the mouse. To prevent this from happening, her body manufactures and purposefully uses a special stirrup. Before sending an ultrasonic pulse, a special muscle pulls the stirrup away from the window of the cochlea of the inner ear - the vibrations are mechanically interrupted. Essentially, the stirrup also makes a click, but not a sound, but an anti-sound one. After a signal-cry, it immediately returns to its place so that the ear is ready to receive the reflected signal. It is difficult to imagine with what speed the muscle can act, turning off the hearing of the mouse at the moment of the sent impulse-scream. During the pursuit of prey - this is 200-250 impulses per second!
And the butterfly clicks, which are dangerous for a bat, are heard exactly at the moment when the hunter turns on his ear to perceive his echo. So, to make a stunned predator fly away in fright, moth sends signals that are extremely matched to its locator. To do this, the insect's body is programmed to receive the pulse frequency of the approaching hunter and sends a response signal exactly in unison with it.
This relationship between moths and bats raises many questions. How did insects get the ability to perceive the ultrasonic signals of bats and instantly understand the danger they carry? How could butterflies gradually develop an ultrasonic device with perfectly matched protective characteristics through the process of selection and improvement? The perception of ultrasonic signals of bats is also not easy to figure out. The fact is that they recognize their echo among millions of voices and other sounds. And no cries-signals of fellow tribesmen, no ultrasonic signals emitted with the help of equipment, prevent bats from hunting. Only the signals of the butterfly, even artificially reproduced, make the mouse fly away.
Living beings present new and new riddles, causing admiration for the perfection and expediency of the structure of their body.
The praying mantis, like the butterfly, along with excellent eyesight, is also given special hearing organs to avoid meeting with bats. These hearing organs that perceive ultrasound are located on the chest between the legs. And for some species of praying mantis, in addition to the ultrasonic organ of hearing, the presence of a second ear is characteristic, which perceives much lower frequencies. Its function is not yet known.
chemical feeling
Animals are endowed with a general chemical sensitivity, which is provided by various sensory organs. The chemical sense of insects has the most significant role smell plays. And termites and ants, according to scientists, are given a three-dimensional sense of smell. What it is is hard for us to imagine. The olfactory organs of an insect react to the presence of even very small concentrations of a substance, sometimes very remote from the source. Thanks to the sense of smell, the insect finds prey and food, navigates the terrain, learns about the approach of the enemy, and carries out biocommunication, where the specific “language” is the exchange of chemical information using pheromones.
Pheromones are the most complex compounds secreted for communication purposes by some individuals in order to transfer information to other individuals. Such information is encoded in specific chemicals, depending on the type of living being and even on its belonging to a particular family. Perception with the help of the olfactory system and decoding of the "message" causes a certain form of behavior or physiological process in the recipients. To date, a significant group of insect pheromones is known. Some of them are designed to attract individuals of the opposite sex, others, trace ones, indicate the path to a home or food source, others serve as an alarm signal, fourth ones regulate certain physiological processes, etc.
Truly unique should be the "chemical production" in the body of insects in order to release in the right amount and at a certain moment the whole range of pheromones they need. Today, more than a hundred of these substances of the most complex nature are known. chemical composition, but no more than a dozen of them were artificially reproduced. Indeed, to obtain them, advanced technologies and equipment are required, so for now it remains only to be surprised at such an arrangement of the body of these miniature invertebrate creatures.
Beetles are provided mainly with olfactory type antennae. They allow you to capture not only the smell of a substance and the direction of its distribution, but even "feel" the shape of an odorous object. An example of a great sense of smell is gravedigger beetles, engaged in cleaning the earth from carrion. They are able to smell hundreds of meters from her and gather big group. And the ladybug, with the help of smell, finds colonies of aphids in order to leave masonry there. After all, not only she herself feeds on aphids, but also her larvae.
Not only adult insects, but also their larvae are often endowed with an excellent sense of smell. Thus, the larvae of the cockchafer are able to move to the roots of plants (pine, wheat), guided by a slightly elevated concentration of carbon dioxide. In experiments, the larvae immediately go to the soil area, where they introduced a small amount of a substance that forms carbon dioxide.
The sensitivity of the olfactory organ, for example, of the Saturnian butterfly, the male of which is able to capture the smell of a female of its own species at a distance of 12 km, seems incomprehensible. When comparing this distance with the amount of pheromone secreted by the female, a result that surprised scientists was obtained. Thanks to his antennae, the male unmistakably searches among many odorous substances for one single molecule of the hereditarily known substance per 1 m3 of air!
Some Hymenoptera are given such a keen sense of smell that it is not inferior to the well-known instinct of a dog. So, female riders, when running along a tree trunk or stump, vigorously move their antennae. With them, they “sniff out” the larvae of the horntail or lumberjack beetle, located in the wood at a distance of 2–2.5 cm from the surface.
Thanks to the unique sensitivity of the antennae, the tiny helis rider determines by just touching the cocoons of spiders what is in them - whether they are underdeveloped testicles, sedentary spiders that have already left them, or testicles of other riders of their species. How Helis makes such an accurate analysis is not yet known. Most likely, he feels the subtlest specific smell, but it may be that when tapping his antennae, the rider picks up some kind of reflected sound.
The perception and analysis of chemical stimuli acting on the olfactory organs of insects is carried out by a multifunctional system - the olfactory analyzer. It, like all other analyzers, consists of a perceiving, conducting and central departments. Olfactory receptors (chemoreceptors) perceive molecules of odorous substances, and impulses signaling a certain smell are sent along the nerve fibers to the brain for analysis. There is an instant development of the response of the body.
Speaking about the sense of smell of insects, one cannot but say about the smell. In science, there is still no clear understanding of what a smell is, and there are many theories regarding this natural phenomenon. According to one of them, the analyzed molecules of a substance represent a “key”. And the “lock” is the receptors of the olfactory organs included in the odor analyzers. If the configuration of the molecule approaches the "lock" of a certain receptor, then the analyzer will receive a signal from it, decipher it and transmit information about the smell to the animal's brain. According to another theory, the smell is determined by the chemical properties of the molecules and the distribution of electrical charges. The newest theory, which has won many supporters, sees the main cause of smell in the vibrational properties of molecules and their constituents. Any fragrance is associated with certain frequencies (wave numbers) of the infrared range. For example, onion soup thioalcohol and decaborane are chemically completely different. But they have the same frequency and the same smell. At the same time, there are chemically similar substances that are characterized by different frequencies and smell differently. If this theory is correct, then both aromatic substances and thousands of types of cells that perceive smell can be assessed by infrared frequencies.
"Radar installation" of insects
Insects are endowed with excellent organs of smell and touch - antennae (antennae or shackles). They are very mobile and easily controlled: an insect can breed them, bring them together, rotate each one individually on its own axis or together on a common one. In this case, they both outwardly resemble and in essence are a “radar installation”. The nerve-sensitive element of the antennae are the sensilla. From them, an impulse at a speed of 5 m per second is transmitted to the "brain" center of the analyzer to recognize the object of irritation. And then the signal of response to the received information instantly goes to the muscle or other organ.
In most insects, on the second segment of the antennae, there is a Johnston organ - a universal device, the purpose of which has not yet been fully elucidated. It is believed that it perceives movements and tremors of air and water, contacts with solid objects. Locusts and grasshoppers are endowed with surprisingly high sensitivity to mechanical vibrations, which are able to register any vibrations with an amplitude equal to half the diameter of a hydrogen atom!
Beetles also have a Johnston organ on the second segment of the antennae. And if a beetle running on the surface of the water is damaged or removed, then it will stumble upon any obstacles. With the help of this organ, the beetle is able to capture reflected waves coming from the coast or obstacles. He feels water waves with a height of 0.000000004 mm, that is, the Johnston organ performs the task of an echo sounder or radar.
Ants are distinguished not only by a well-organized brain, but also by an equally perfect bodily organization. The antennae are of paramount importance for these insects; some serve as an excellent organ of smell, touch, knowledge of the environment, and mutual explanations. Ants deprived of antennae lose the ability to find a way, nearby food, and distinguish enemies from friends. With the help of antennas, insects are able to "talk" among themselves. Ants transmit important information by touching each other's antennae with their antennae. In one of the behavioral episodes, two ants found prey in the form of larvae of different sizes. After "negotiations" with their brothers with the help of antennas, they went to the place of discovery together with mobilized assistants. At the same time, the more successful ant, which managed to transmit information about the larger prey it found with the help of antennae, mobilized a much larger group of worker ants behind it.
Interestingly, ants are one of the cleanest creatures. After each meal and sleep, their entire body and especially the antennae are thoroughly cleaned.
Taste sensations
A person clearly defines the smell and taste of a substance, while in insects, taste and olfactory sensations are often not separated. They act as a single chemical feeling (perception).
Insects with taste sensations prefer one or another substance depending on the nutrition characteristic of a given species. At the same time, they are able to distinguish between sweet, salty, bitter and sour. For contact with the food consumed, the taste organs can be located on various parts of the body of insects - on the antennae, proboscis and legs. With their help, insects receive basic chemical information about the environment. For example, a fly, only by touching its paws to an object of interest to it, almost immediately finds out what is under its feet - drink, food or something inedible. That is, it is capable of performing instant contact analysis of a chemical with its feet.
Taste is the sensation that occurs when a solution of chemicals is exposed to the receptors (chemoreceptors) of the insect's taste organ. Receptor taste cells are the peripheral part of the complex system of the taste analyzer. They perceive chemical stimuli, and here the primary coding of taste signals occurs. Analyzers immediately transmit volleys of chemoelectric impulses along thin nerve fibers to their "brain" center. Each such pulse lasts less than a thousandth of a second. And then the central structures of the analyzer instantly determine the taste sensations.
Attempts are continuing to understand not only the question of what a smell is, but also to create a unified theory of "sweetness". So far, this has not been successful - maybe you, the biologists of the 21st century, will succeed. The problem is that completely different chemicals, both organic and inorganic, can create relatively the same taste sensation of sweetness.
sense organs
The study of the sense of touch of insects is perhaps the greatest difficulty. How do these creatures chained in a chitinous shell touch the world? So, thanks to skin receptors, we are able to perceive various tactile sensations - some receptors register pressure, others temperature, etc. Touching an object, we can conclude that it is cold or warm, hard or soft, smooth or rough. Insects also have analyzers that determine temperature, pressure, etc., but much in the mechanisms of their action remains unknown.
The sense of touch is one of the most important senses for the flight safety of many flying insects, to sense air currents. For example, in dipterans, the entire body is covered with sensilla, which perform tactile functions. There are especially many of them on the halteres in order to perceive air pressure and stabilize the flight.
Thanks to the sense of touch, the fly is not so easy to swat. Her vision allows her to notice a threatening object only at a distance of 40 - 70 cm. But the fly is able to respond to a dangerous movement of the hand, which caused even a small movement of air, and instantly take off. This ordinary housefly once again confirms that nothing is simple in the living world - all creatures, young and old, are provided with excellent sensory systems for active life and their own protection.
Insect receptors that register pressure can be in the form of pimples and bristles. They are used by insects for various purposes, including for orientation in space - in the direction of gravity. For example, a fly larva always moves clearly upwards before pupation, that is, against gravity. After all, she needs to crawl out of the liquid food mass, and there are no landmarks there, except for the attraction of the Earth. Even after getting out of the chrysalis, the fly tends to crawl up for some time until it dries out in order to fly.
Many insects have a well-developed sense of gravity. For example, ants are able to estimate a surface slope of 20. And a rove beetle that digs vertical burrows can estimate a deviation from the vertical of 10.
Living "forecasters"
Many insects are endowed with an excellent ability to anticipate weather changes and make long-term forecasts. However, this is typical for all living things - be it a plant, a microorganism, an invertebrate or a vertebrate. Such abilities ensure normal life activity in their intended habitat. There are also rarely observed natural phenomena - droughts, floods, sharp cold snaps. And then, in order to survive, living beings need to mobilize additional protective equipment in advance. In both cases, they use their internal "weather stations".
Constantly and carefully observing the behavior of various living beings, one can learn not only about weather changes, but even about upcoming natural disasters. After all, over 600 species of animals and 400 species of plants, so far known to scientists, can play a kind of role as barometers, indicators of humidity and temperature, predictors of both thunderstorms, storms, tornadoes, floods, and beautiful cloudless weather. Moreover, there are live "weather forecasters" everywhere, wherever you are - by the reservoir, in the meadow, in the forest. For example, before the rain, even with a clear sky, the green grasshoppers stop chirping, the ants begin to tightly close the entrances to the anthill, and the bees stop flying for nectar, sit in the hive and buzz. In an effort to hide from the impending bad weather, flies and wasps fly into the windows of houses.
Observations for poisonous ants, living in the foothills of Tibet, revealed their excellent ability to make more distant forecasts. Before the onset of a period of heavy rains, ants move to another place with dry hard ground, and before the onset of a drought, ants fill dark, moist depressions. Winged ants are able to feel the approach of a storm in 2–3 days. Large individuals begin to rush along the ground, while small ones swarm at a low altitude. And the more active these processes are, the stronger bad weather is expected. It was found that during the year the ants correctly identified 22 weather changes, and were mistaken only in two cases. This amounted to 9%, which looks quite good compared to the average error of weather stations of 20%.
The purposeful actions of insects often depend on long-term forecasts, and this can be of great service to people. An experienced beekeeper is provided with a fairly reliable forecast by bees. For the winter, they close up the notch in the hive with wax. By the opening for ventilation of the hive, one can judge the upcoming winter. If the bees leave a large hole, the winter will be warm, and if it is small, expect severe frosts. It is also known that if the bees start to fly out of the hives early, an early warm spring can be expected. The same ants, if the winter is not expected to be severe, remain to live near the surface of the soil, and before a cold winter, they settle down deeper in the ground and build a higher anthill.
In addition to the macroclimate for insects, the microclimate of their habitat is also important. For example, bees do not allow overheating in the hives and, having received a signal from their living "devices" about the temperature exceeding, they begin to ventilate the room. Part of the worker bees is organized at different heights throughout the hive and sets the air in motion with quick wing beats. A strong air current is formed, and the hive is cooled. Ventilation is a long process, and when one batch of bees gets tired, it is the turn of another, and in strict order.
The behavior of not only adult insects, but also their larvae, depends on the readings of living "instruments". For example, cicada larvae that develop in the ground come to the surface only when the weather is good. But how do you know what the weather is like at the top? To determine this, they create special earthen cones with large holes above their underground shelters - a kind of meteorological structures. In them, cicadas assess temperature and humidity through a thin layer of soil. And if the weather conditions are unfavorable, the larvae return to the mink.
The phenomenon of forecasting rainstorms and floods
Observing the behavior of termites and ants in critical situations can help people predict heavy rainfall and flooding. One of the naturalists described the case when, before the flood, an Indian tribe living in the jungles of Brazil hurriedly left their settlement. And the ants "told" the Indians about the approaching disaster. Before the flood, these social insects become very agitated and urgently leave the habitable place along with the pupae and food supplies. They go to places where water does not reach. The local population hardly understood the origins of such an amazing sensitivity of ants, but, obeying their knowledge, people left the trouble after the little weather forecasters.
They are excellent at predicting floods and termites. Before it starts, they leave their homes with the whole colony and rush to the nearest trees. Anticipating the magnitude of the disaster, they rise to exactly the height that will be higher than the expected flood. There they wait until the muddy streams of water subside, which rush at such a speed that trees sometimes fall under their pressure.
A huge number of weather stations monitor the weather. They are located on land, including in the mountains, on specially equipped scientific vessels, satellites and space stations. Meteorologists are equipped with modern instruments, devices and computers. In fact, they do not make a weather forecast, but a calculation, a calculation of weather changes. And the insects in the above examples of the real predict the weather using innate abilities and special living “devices” built into their bodies. Moreover, weather forecasting ants determine not only the time of the approach of the flood, but also estimate its scope. After all, for a new refuge, they occupied only safe places. Scientists have not yet been able to explain this phenomenon. Termites presented an even greater mystery. The fact is that they were never located on those trees that, during a flood, turned out to be demolished by stormy streams. In a similar way, according to the observation of ethologists, the starlings behaved, which in the spring did not occupy the birdhouses dangerous for the settlement. Subsequently, they were really torn off by a hurricane wind. But here we are talking about a relatively large animal. The bird, perhaps by swinging the birdhouse or by other signs, assesses the unreliability of its fastening. But how and with the help of what devices can such forecasts be made by very small, but very "wise" animals? Man is not only not yet able to create anything like this, but he cannot answer. These tasks are for future biologists!
Bibliography
For the preparation of this work, materials from the site were used. http://www.portal-slovo.ru/
Zhdanova T. D.
Coming into contact with the varied and energetic activities of the insect world can be an amazing experience. It would seem that these creatures carelessly fly and swim, run and crawl, buzz and chirp, gnaw and carry. However, all this is not done aimlessly, but mainly with a certain intention, according to the innate program embedded in their body and the acquired life experience. For the perception of the surrounding world, orientation in it, the implementation of all expedient actions and life processes, animals are endowed with very complex systems, primarily nervous and sensory.
What do the nervous systems of vertebrates and invertebrates have in common?
Nervous system is a complex complex of structures and organs, consisting of nervous tissue, where the central section is the brain. The main structural and functional unit of the nervous system is a nerve cell with processes (in Greek, a nerve cell is a neuron).
The nervous system and the brain of insects provide: perception with the help of the senses of external and internal irritation (irritability, sensitivity); instant processing by the system of analyzers of incoming signals, preparation and implementation of an adequate response; storage in memory in an encoded form of hereditary and acquired information, as well as its instantaneous retrieval as needed; management of all organs and systems of the body for its functioning as a whole, balancing it with the environment; implementation of mental processes and higher nervous activity, expedient behavior.
The organization of the nervous system and brain of vertebrates and invertebrates is so different that at first glance it seems impossible to compare them. And at the same time, for the most diverse types of the nervous system, belonging, it would seem, to both completely “simple” and “complex” organisms, the same functions are characteristic.
The very tiny brain of a fly, bee, butterfly or other insect allows it to see and hear, touch and taste, move with great accuracy, and moreover, fly using an internal “map” over considerable distances, communicate with each other and even own its own "language", to learn and apply logical thinking in non-standard situations. So, the brain of an ant is much smaller than a pinhead, but this insect has long been considered a "sage". When compared not only with his microscopic brain, but also with the incomprehensible capabilities of a single nerve cell, a person should be ashamed of his most modern computers. And what can science say about this, for example, neurobiology, which studies the processes of birth, life and death of the brain? Was she able to unravel the mystery of the vital activity of the brain - this most complex and mysterious of the phenomena known to people?
The first neurobiological experience belongs to the ancient Roman physician Galen. Having cut the nerve fibers in a pig, with the help of which the brain controlled the muscles of the larynx, he deprived the animal of its voice - it immediately became numb. It was a millennium ago. But how far has science gone since then in its knowledge of the principle of the brain? It turns out that despite the enormous work of scientists, the principle of operation of even one nerve cell, the so-called "brick" from which the brain is built, is still not known to man. Neuroscientists understand a lot about how a neuron "eats" and "drinks"; how it receives the energy necessary for its life activity, digesting the necessary substances extracted from the environment in “biological boilers”; how then this neuron sends the most various information in the form of signals, encrypted either in a certain series of electrical impulses, or in various combinations of chemicals. And then what? Here a nerve cell received a specific signal, and in its depths a unique activity began in collaboration with other cells that form the brain of an animal. There is a memorization of the incoming information, the extraction of the necessary information from the memory, decision-making, giving orders to the muscles and various organs, etc. How is everything going? Scientists don't know for sure yet. Well, since it is not clear how individual nerve cells and their complexes operate, the principle of operation of the whole brain, even as small as that of an insect, is not clear either.
The work of the sense organs and living "devices"
The vital activity of insects is accompanied by the processing of sound, olfactory, visual and other sensory information - spatial, geometric, quantitative. One of the many mysterious and interesting features of insects is their ability to accurately assess the situation using their own "instruments". Our knowledge of these devices is limited, although they are widely used in nature. These are determinants of various physical fields, which allow predicting earthquakes, volcanic eruptions, floods, weather changes. This is a sense of time, counted by the internal biological clock, and a sense of speed, and the ability to navigate and navigate, and much more.
The property of any organism (microorganisms, plants, fungi and animals) to perceive stimuli emanating from the external environment and from their own organs and tissues is called sensitivity. Insects, like other animals with a specialized nervous system, have nerve cells with a high selectivity for various stimuli - receptors. They can be tactile (responsive to touch), temperature, light, chemical, vibrational, muscular-articular, etc. Thanks to their receptors, insects capture the whole variety of environmental factors - various vibrations (a wide range of sounds, radiation energy in the form of light and heat), mechanical pressure (for example, gravity) and other factors. Receptor cells are located in tissues either singly or assembled into systems with the formation of specialized sensory organs - sense organs.
All insects perfectly "understand" the indications of their sense organs. Some of them, like the organs of vision, hearing, smell, are remote and are able to perceive irritation at a distance. Others, like the organs of taste and touch, are contact and respond to exposure through direct contact.
Insects in the mass are endowed with excellent vision. Their complex compound eyes, to which simple eyes are sometimes added, serve to recognize various objects. Some insects are provided with color vision, suitable night vision devices. Interestingly, the eyes of insects are the only organ that other animals have the likeness of. At the same time, the organs of hearing, smell, taste and touch do not have such a similarity, but, nevertheless, insects perfectly perceive smells and sounds, navigate in space, capture and emit ultrasonic waves. Delicate sense of smell and taste allow them to find food. A variety of glands of insects secrete substances to attract brothers, sexual partners, scare off rivals and enemies, and a highly sensitive sense of smell is able to detect the smell of these substances even for several kilometers.
Many in their ideas associate the sense organs of insects with the head. But it turns out that the structures responsible for collecting information about the environment are found in insects in various parts of the body. They can determine the temperature of objects and taste food with their feet, detect the presence of light with their backs, hear with their knees, whiskers, tail appendages, body hairs, etc.
The sense organs of insects are part of sensory systems - analyzers that penetrate the network of almost the entire organism. They receive many different external and internal signals from the receptors of their sense organs, analyze them, form and transmit "instructions" to various organs for the implementation of appropriate actions. The sense organs mainly make up the receptor section, which is located on the periphery (ends) of the analyzers. And the conductive department is formed by central neurons and pathways from receptors. There is in the brain certain areas to process information from the senses. They constitute the central, “brain”, part of the analyzer. Thanks to such a complex and expedient system, for example, a visual analyzer, an accurate calculation and control of the organs of movement of an insect is carried out.
Extensive knowledge has been accumulated about the amazing capabilities of the sensory systems of insects, but the volume of the book allows us to cite only a few of them.
organs of vision
Eyes and the entire most complex visual system are an amazing gift, thanks to which animals are able to receive basic information about the world around them, quickly recognize various objects and evaluate the situation that has arisen. Vision is necessary for insects when searching for food to avoid predators, to explore objects of interest or environment, to interact with other individuals in reproductive and social behavior, etc.
Insects are equipped with a variety of eyes. They can be complex, simple or additional eyes, as well as larval. The most complex are compound eyes, which consist of a large number of ommatidia that form hexagonal facets on the surface of the eye. Ommatidium is essentially a tiny visual apparatus, equipped with a miniature lens, a light guide system and light-sensitive elements. Each facet perceives only a small part of the object, and together they provide a mosaic image of the entire object. Compound eyes, characteristic of most adult insects, are located on the sides of the head. In some insects, for example, a hunter dragonfly, which quickly reacts to the movement of prey, the eyes occupy half of the head. Each of her eyes is built from 28,000 facets. For comparison, butterflies have 17,000 of them, and a housefly has 4,000. Eyes on the head of insects can be two or three on the forehead or crown, and less often on its sides. Larval ocelli in beetles, butterflies, hymenoptera in adulthood are replaced by complex ones.
The general plan of the structure of the nervous system of insects is the same as that of other arthropods. Along with cases of strong dissection (supraoesophageal, suboesophageal, 3 thoracic and 8 abdominal ganglia) and pair structure of the nervous system in primitive insects, there are cases of extreme concentration of the nervous system: the entire abdominal chain can be reduced to a continuous ganglionic mass, which is especially common in larvae and larval adults in the absence of limbs and a weak dismemberment of the body.
In the supraesophageal ganglion, the development of the internal structure of the protocerebral part of the brain, in particular, the mushroom bodies, forming 1-2 pairs of tubercles on the sides of the midline, is noticeable. The brain is well developed, and especially its anterior section, in which there are special paired formations responsible for complex forms of behavior.
Among the organs, represented by numerous hairs, bristles, depressions - to which the nerve endings fit - various receptors that perceive different types stimuli - mechanical, chemical, temperature, and so on, the sense organs of touch and smell prevail in their significance. The organs of mechanical sense include both the organs of touch and the organs of hearing, which perceive air vibrations as sounds. The organs of touch are represented on the surface of the body of insects by bristles. Organs of chemical sense - serve to perceive the chemistry of the environment (taste and smell). The olfactory receptors, also in the form of a bristle - sometimes changing into thin-walled detached outgrowths, non-segmented finger-like protrusions, thin-walled flat areas of the integument, are most often located on the antennae, taste - on the organs of the oral apparatus, but sometimes on other parts of the body - in flies, for example, - on the terminal segments of the legs. The sense of smell is of great importance in intra- and interpopulation relations of insect individuals.
With the help of complex compound eyes, consisting of sensilla, the hexagonal parts of which are called facets, form a cornea from a transparent cuticle - insects are able to distinguish the sizes, shapes and colors of objects. The honey bee, for example, can see all the same colors as humans, except for red, but also ultraviolet colors that are invisible to the human eye. Simple eyes of insects - reacting to the degree of illumination, ensure the stability of image perception with compound eyes, but are not able to distinguish color and shape.
Insects of some orders, the species of which have males with sound organs - for example, orthoptera - have tympanal organs, the structure of which suggests that these are organs of hearing. In grasshoppers and crickets, they are on the lower leg under knee joint, in locusts and cicadas - on the sides of the first abdominal segment and externally represented by a depression (sometimes surrounded by a fold of cover) with a thinly stretched membrane at the bottom, on the inner surface of which or near it is a nerve ending of a peculiar structure; some other insects have wings, etc.
The basis of the sense organs is the so-called neuro-sensitive formations - sensilla, which look like hairs, bristles, depressions.
Insects have the following sense organs:
1) Organs of mechanical sense. These include tactile sensilla scattered throughout the body. They perceive the shaking of the air, feel the position of the body in space, etc. The organs of mechanical sense also include organs hearing, for they perceive sound, which is known to be vibrations of the air. The organs of hearing are predominantly in insects capable of making sounds. They are located on the sides of the abdomen, on the wings, fore legs and in some other places.
2) The chemical sense organs are represented by chemoreceptor sensilla and serve to perceive the chemistry of the environment, i.e. odors and taste sensations. They are located on the mouth limbs, antennae, sometimes (in bees) on the legs. The chemical sense - the sense of smell - plays an important role in intra- and interpopulation relations of insects. Organs; vision is represented by complex (faceted) and simple eyes. The eye itself is made up of many sensilla. The surface hexagonal part is called a facet. The facets form the cornea, which is a transparent cuticle.
sensory neurons
The bodies of sensory or sensory cells, usually of a bipolar or multipolar form, always lie near the sensory organ or innervated tissue. The dendrites of some neurons, most often bipolar, are associated with cuticular formations, while others, always multipolar, are connected with the tissues of the body cavity or they form a subepidermal network, as in soft-skinned larvae.
Accordingly, two broad categories of sensory cells are distinguished. Cells of the first type differ in that they are almost always associated with the cuticle or its protrusions: apodemes, tracheae, lining of the preoral and oral cavities, etc. They include a variety of exteroreceptor cells, including visual ones, although their dendrites are not clearly expressed. Cells of the second type are never associated with the cuticle and lie only on the inner surface of the body, the walls of the digestive tract, in muscle and connective tissues. They are electrophysiologically shown to belong to intero or proprioceptors.
Axons of sensory cells go directly to the corresponding ganglia of the CNS, sometimes located directly in the brain, for example, optical or olfactory centers. The question of the channels of communication between receptor cells and the nerve center is extremely important for the correct interpretation of the work of the analyzer and the mechanism for controlling the behavior of an insect. Now, apparently, everyone recognizes as untenable the former opinion that in some receptor systems, for example, in the antennae of the bug Rhodnius, the axons of several sensory cells fuse into a single fiber. But the closure of a group of receptors to one peripheral neuron of the second order, i.e., the loss of the "address" of the input signal, is characteristic of the first optical ganglion of insects. The meaning of such a method of communication with the center, leading to a partial loss of information from a set of sensors, is not always clear yet (see below).
Nervous tissue, including sensory cells, originate from the ectoderm. Their belonging to the cover of the body is also expressed in the fact that the connection of the sensory organ with the central nervous system is established centripetally. So, V. Wigglesworth showed on the bug Rhodnius that the cut afferent nerve regenerates in the direction of the central nervous system. Similarly, during each molt, when additional receptors are formed to serve the increasing body surface, their sensory cells send out axons centripetally.
The fact of centripetal development of the axon revealed on histological preparations can become one of the grounds for the important conclusion that the path from the sensory cell to the CNS is direct, without synaptic switching. Near the receptor cells and afferent nerves, there are others, such as neuroglial (feeder) cells, but they are not related to the transmission of the receptor signal.
The sense organs of insects are differentiated and well developed. The organs of touch and smell predominate in their significance. The organs of touch are externally represented by bristles. The olfactory organs also have the shape of a typical seta, which, changing, can turn into detached thin-walled protrusions and non-segmented finger-like protrusions and thin-walled flat areas of the integument. The most important location of the endings of the olfactory nerves are the antennae.
For example, the role of antennae as organs of smell in flies and lepidoptera, which distinguish even faint odors at a great distance. The sense of smell of bees is better studied; it turned out that their ability to perceive smells is close to ours: those smells that we perceive are also perceived by bees, those smells that we mix are mixed by bees; the organs of smell are also concentrated mainly on the antennae. Tastes sweet, bitter, sour, and salty are also distinguished by insects; taste organs are located on the tentacles of the mouth parts, on the legs; the sharpness of the taste sensation in different organs of the same insect may be different; it is much higher than in humans. compound eyes insects perceive the movement of objects, in some cases they can also perceive the shape of objects; higher hymenoptera (bees) can also perceive colors, including those that are not perceived by humans (“ultraviolet”); however, color vision is not as diverse as in humans: for example, a bee in the left side of the spectrum feels yellow, other colors are like shades of yellow; the right blue-violet part of the spectrum is also perceived by bees as a single color. The visual acuity of bees is much lower than that of humans.
In some orders, such as in the order of Orthoptera (Orthoptera), which include grasshoppers, crickets and locusts, the so-called tympanal organs are widespread. to assume auditory organs in the tympanal organs. Tympanal organs in grasshoppers and crickets are located on the lower leg under the knee joint, while in locusts and cicadas on the sides of the first abdominal segment, they are externally represented by a depression, sometimes surrounded by a fold of cover and with a thin stretched membrane at the bottom; on the inner surface of the membrane or in its immediate vicinity there is a nerve ending of a peculiar structure.
Insects in the mass are endowed with excellent vision. Their complex compound eyes, to which simple eyes are sometimes added, serve to recognize various objects. Some insects are provided with color vision, suitable night vision devices. Interestingly, the eyes of insects are the only organ that other animals have the likeness of. At the same time, the organs of hearing, smell, taste and touch do not have such a similarity, but, nevertheless, insects perfectly perceive smells and sounds, navigate in space, capture and emit ultrasonic waves. Delicate sense of smell and taste allow them to find food. A variety of glands of insects secrete substances to attract brothers, sexual partners, scare off rivals and enemies, and a highly sensitive sense of smell is able to detect the smell of these substances even for several kilometers.
Many in their ideas associate the sense organs of insects with the head. But it turns out that the structures responsible for collecting information about the environment are found in insects in various parts of the body. They can determine the temperature of objects and taste food with their feet, detect the presence of light with their backs, hear with their knees, whiskers, tail appendages, body hairs, etc.
The sense organs of insects are part of sensory systems - analyzers that penetrate the network of almost the entire organism. They receive many different external and internal signals from the receptors of their sense organs, analyze them, form and transmit "instructions" to various organs for the implementation of appropriate actions. The sense organs mainly make up the receptor section, which is located on the periphery (ends) of the analyzers. And the conductive department is formed by central neurons and pathways from receptors. The brain has certain areas for processing information coming from the senses. They constitute the central, “brain”, part of the analyzer. Thanks to such a complex and expedient system, for example, a visual analyzer, an accurate calculation and control of the organs of movement of an insect is carried out.
Extensive knowledge has been accumulated about the amazing capabilities of the sensory systems of insects, but the volume of the book allows us to cite only a few of them.
organs of vision
Eyes and the entire most complex visual system are an amazing gift, thanks to which animals are able to receive basic information about the world around them, quickly recognize various objects and evaluate the situation that has arisen. Vision is necessary for insects when searching for food to avoid predators, to explore objects of interest or environment, to interact with other individuals in reproductive and social behavior, etc.
Insects are equipped with a variety of eyes. They can be complex, simple or additional eyes, as well as larval. The most complex are compound eyes, which consist of a large number of ommatidia that form hexagonal facets on the surface of the eye. Ommatidium is essentially a tiny visual apparatus, equipped with a miniature lens, a light guide system and light-sensitive elements. Each facet perceives only a small part of the object, and together they provide a mosaic image of the entire object. Compound eyes, characteristic of most adult insects, are located on the sides of the head. In some insects, for example, a hunter dragonfly, which quickly reacts to the movement of prey, the eyes occupy half of the head. Each of her eyes is built from 28,000 facets. For comparison, butterflies have 17,000 of them, and a housefly has 4,000. Eyes on the head of insects can be two or three on the forehead or crown, and less often on its sides. Larval ocelli in beetles, butterflies, hymenoptera in adulthood are replaced by complex ones.
It is curious that insects cannot close their eyes during rest and therefore sleep with their eyes open.
It is the eyes that contribute to the quick reaction of an insect hunter, such as a praying mantis. By the way, this is the only insect that can turn around and look behind itself. Large eyes provide the praying mantis with binocular vision and allow you to accurately calculate the distance to the object of their attention. This ability, combined with the quick forward movement of the front legs towards the prey, make the mantid an excellent hunter.
And in yellow-footed beetles, running on the water, the eyes allow you to simultaneously see the prey both on the surface of the water and under it. To do this, the visual analyzers of the beetle have the ability to correct for the refractive index of water.
The perception and analysis of visual stimuli is carried out by the most complex system - the visual analyzer. For many insects, this is one of the main analyzers. Here, the primary sensitive cell is the photoreceptor. And the pathways (optic nerve) and other nerve cells located at different levels of the nervous system are connected with it. When perceiving light information, the sequence of events is as follows. The received signals (light quanta) are instantly encoded in the form of impulses and transmitted along the conducting paths to the central nervous system - to the "brain" center of the analyzer. There, these signals are immediately decoded (decoded) into the corresponding visual perception. For its recognition, standards of visual images and other necessary information are retrieved from memory. And then a command is sent to various organs for an adequate response of the individual to a change in the situation.
