External structure of insects. Internal structure of insects. Insect sense organs

External structure of insects.Insects differ from other representatives of the arthropod phylum mainly by the division of the body into three sections - head, thorax and abdomen, and by the presence of 3 pairs of legs and usually 2 pairs of wings on the thoracic region). The body of insects is covered with a cuticular (chitinous) covering and is divided into rings (segments). The thoracic region consists of 3 segments - prothoracic, mesothoracic and metathorax, the abdominal region - usually of 10 segments. The dorsal part of the thoracic segments is called the anterior, mid- and metanotum. The dorsal part of the last abdominal segment is called the anal plate, and its abdominal part is called the genital plate.

The head of insects consists of an undivided head capsule, on the sides of which there are large compound eyes. Its front surface is called the forehead (downward from the forehead there is a clypeus), the top is the crown, the back is the back of the head, and the sides are the temples (behind the eyes) and cheeks (below the eyes). In addition to compound eyes, there are often small lens-shaped transparent eyes on the crown; Usually there are 3 eyes.

Antennae are attached to the front surface of the head, which can be filamentous (thin, of the same thickness throughout), setalike (thin, thinning towards the end), beetle-shaped (with sharp interceptions between short cylindrical or rounded segments), xiphoid (flattened and expanded at the base ), clavate (with a widening at the end), serrate (with irregularly triangular compacted segments, the edge of which protrudes at an angle), comb (with long fleshy projections at the ends of the segments), pinnate (with thin hair-like projections on the segments), lamellar (with several plates on end), geniculate (bent at an angle, with a greatly elongated main segment) or have an irregular shape. The number of antennal segments can vary from 2-3 to several dozen. The length of the antennae can be several times greater than the length of the body.

The mouthparts are attached to the head from below. When viewing the head from the front, the upper lip is visible, which is an unpaired plate movably connected to the clypeus. On the sides of the upper lip there are massive mandibles. Examining the head from below, it is easy to identify the lower lip, which is a median unpaired plate equipped at the end with short labial palps. On the sides of this plate are the lower jaws, bearing on the outer surface a long articulated maxillary palp. This structure is characteristic of a typical gnawing mouthpart. Insects that feed on liquid food have a mouthparts modified into a piercing or sucking proboscis. Sometimes the mandibles are not part of the proboscis and function normally - this type of oral apparatus is called gnawing-licking or gnawing-sucking. Some insects have underdeveloped mouthparts.

Each thoracic segment carries a pair of legs, respectively the front, middle and hind legs. The main segment of the leg, the coxa, is placed in a special coxal cavity on the underside of the thoracic segment. This is followed by a short trochanter, a long and often thickened femur, an equally long tibia and a tarsus consisting of several segments, usually ending in two claws. Many insects have suckers under their claws. There are often spikes on the shin, and movable spurs at its end. Depending on the structure and function, the legs can be walking, running, jumping, swimming, digging, grasping, etc. On the posterior edge of the chest there is a small, usually more or less triangular protrusion - the scute.

Most insects have two pairs of wings attached to the dorsal part of the thorax; the anterior pair is located on the meso-thorax, the posterior pair - on the metathorax. In some insects, the forewings are leathery, and sometimes strongly sclerotized and durable. They have protective functions, covering at rest the rear pair of wings used for flight, and are called elytra. Some groups of insects do not have wings, but sometimes only one (front or, less commonly, rear) pair of wings is well developed. The wing is distinguished by a base and apex, as well as anterior, outer and posterior edges. When identifying certain species and groups of insects, the venation of the wing, i.e., the features of the pattern formed by the hard veins that serve as a framework for the wing membrane, becomes important.

The veins, according to their direction, are divided into longitudinal and transverse, with the main ones being the longitudinal veins. Along the edge of the wing runs the so-called costal vein (C), which sometimes goes around the entire wing. The next vein, branching at the base of the wing and running parallel to the costal vein, is called the subcostal (Sc). It can be divided into several branches (Sc1, Sc2, etc.). The next two vein stems, which branch off at the base of the wing, are especially important. The first of these trunks - radial (R) - branches into a whole cluster of radial veins, which, in accordance with the order of their merging with the leading edge of the wing, are designated as first radial (R1), second radial (R 2), third radial (R3), etc. e. The second trunk - medial (M) - can also branch and in the same order forms the first medial (M1), second medial (M2), third medial (M3) and subsequent veins. The posterior edge of the wing is also strengthened by cubital veins (Cu 1, Cu 2, etc.) extending from the base of the wing with a single cubital trunk (Cu), of which there are usually two. The fan of veins is completed by several non-branching anal veins (A1, A2, A3, etc.).

The space between the veins is called the field, which is designated by the name of the vein in front. The field is divided into cells by transverse veins: in the radial sector - radial, in the medial - medial, etc. At the base of the wing, basal cells are distinguished, and between the radial and medial sectors - one or more discoidal ones. If there are many cross-veins and, therefore, cells, the venation is called reticulate; if there are several cross-veins limiting large cells, then cellular. At the front edge of the wing there is often a small darkened area - the wing ocellus. The surface of the wing may be covered with hairs, scales or other cuticular formations.

The abdomen of insects is equipped with various appendages, usually located only at the very end. These are mainly long thin caudal filaments or shorter paired cerci. Females often develop a hard, needle-shaped (saber-shaped) or soft, usually retractable ovipositor. Sometimes there is a sting. Only a few insects have developed appendages on the underside of the abdominal segments: paired outgrowths or a kind of jumping fork.

Literature: B.M. Mamaev, L.N. Medvedev, F. N. Pravdin. Key to insects of the European part of the USSR. Moscow, "Enlightenment", 1976

Insects are the most numerous class of arthropod invertebrates. According to various estimates, their number reaches 3 million species. To date, about 1 million species of insects have been described, which is approximately 70% of the total known fauna. Representatives of the insect class are found everywhere and play a significant role in most ecological communities.

The defining characteristics of insects are the presence of a pair of antennae, three pairs of legs and three body sections (tagmas): head, thorax and abdomen.

Spider insect. Photo: Jon Sullivan

The position of insects in the system of modern classification of living nature:

Kingdom Animalia (= Metazoa; Animals)

Subkingdom Eumetazoa

Section Bilateria (= Triploblastica; Three-layered)

Subsection Protostomia (Protostomes)

Phylum Arthropoda (Arthropods)

Subphylum Atelocerata (= Tracheata, Antennata; Incomplete)

Class Insecta – Insects

Insects can be characterized as bilaterally symmetrical protostomes with a segmented body covered with a chitinous capsule; they are the most evolutionarily advanced class of Arthropods - the highest type of invertebrate animals.

Insect body structure

The insect's body is segmented. The head consists of a head lobe (acron) and 4 segments; chest - of 3 segments. The abdomen consists of 4–11 segments and an anal lobe (telson). The insect's body is covered with a chitinous shell (cuticle), which performs a barrier function, prevents excessive evaporation of water and plays the role of an exoskeleton, providing mechanical protection for the body. It forms hard plates - sclerites, connected by thin articular membranes.

External structure of an insect. 1 Eye. 2. Compound (compound) eye. 3. Trochanter. 4. Basin. 6. Front wing. 7. Rear wing. 8. Tympanic membrane. 9. Ovipositor. 10. Anus. 11. Spiracles 12. Hind leg. 13. Metathorax. 14. Middle leg. 15. Mesothorax. 16. Prothorax. 17. Front leg. 18. Thigh 19. Shin. 20. Paw. 21. Claw. 22. Pad. 23. Palp. 24 Antennae.

The chitinous shell is secreted by the hypodermis - a single-layer epithelium lying on the basement membrane; it usually consists of two layers: the epicuticle and the procuticle. The basis of the latter is proteins associated with the nitrogen-containing polysaccharide chitin. It is very durable and in nature is decomposed by a few species of fungi and bacteria that have the enzyme chitinase. The lower layer, in turn, is divided into endocuticle (elastic, gives flexibility to the integument) and exocuticle (provides strength to the integument, therefore it is often sclerotized). The top layer is necessary for land insects to prevent moisture evaporation and desiccation of the body; it consists of four layers and contains a large amount of lipids.

The presence of a chitinous capsule prevents the constant growth of the body, so insects molt: the old chitinous shell lags behind the body, and the epithelium secretes a new one, and until it acquires normal strength, the body grows rapidly

On the insect's head there are compound eyes, between which there may be several simple ocelli, antennae, and mouthparts. The surface of the head capsule (epicranium) is divided into separate sections by sutures. The upper part of the head capsule is called the crown (vertex), it is divided into two halves by the parietal (epicranial) suture. In front, it passes into two frontal sutures delimiting the triangle of the forehead. Outside the frontal sutures are the cheeks (genae), which pass into the crown without visible boundaries. Posteriorly, the crown is bounded by the occipital suture. Behind it, at the level of the cheeks, are the cheeks, and at the level of the crown, the back of the head. Behind them runs the postoccipital suture and the postoccipital. The lower border of the forehead, cheeks and cheeks is a suture, the sections of which are called epistomal, subgenal and hypostomal sutures, respectively.

Insect eyes. “Dragonfly” 1. Facet. 2. Compound eye. 3. Ommatidium. 4. Cornea. 5. Pigment cell. 6. Crystal crystal cone. 7. Sensory cell (visual receptor) 8. Rhabdom. 9. Nerve 10. Basal membrane.

At the lower border of the forehead and above the bases of the lower jaws are structures called tentorial fossae. These are invaginations of the integument that penetrate inside the head capsule and form its internal skeleton - tentorium. The internal skeleton, the fusion of the head segments and their chitinous plates provide special strength to the head capsule.

Complex compound eyes consist of individual ocelli - ommatidia, the eye is covered with a transparent cornea, which has the appearance of a convex hexagon (facet). Under the cornea there is a so-called crystalline (crystalline) cone, together they form the lens of the eye. Light is perceived by receptor (retinal) cells. Their sensitive parts - rhabdomeres - are located in the central part of the ocellus and form a photosensitive element - rhabdom. Along the edges there are pigment cells that isolate one eye from the other.

Pigment cells in diurnal and nocturnal insects differ in the ability of the pigment to move within the cell. In nocturnal insects, pigment can accumulate in the upper part of the cell, while light rays fall on the receptor cells of the neighboring eye and this significantly increases the light sensitivity of the eye.

Compound eyes can include from several hundred to 28,000 (in a dragonfly) ocelli, each capable of perceiving a narrow beam of light rays. As a result, the image of the object is composed of individual “points” (it is mosaic in nature). Such an image is blurry and poorly characterizes the shape of the object. But the advantage of the compound eye is a very wide field of view, which allows you to catch any movement and notice prey or an enemy in time.

Many insects also have simple eyes, consisting of a lens, a layer of sensitive cells, and a cover of pigment cells. At the larval stage, simple eyes have a different structure and disappear during metamorphosis.

Antennae (antennae, collarbone) are appendages of the head lobe. They represent a series of segments of various shapes: bristle-shaped (retina, butterflies, cockroaches), filamentous (wasps, bees, beetles), serrate (moths), comb-like (butterflies, beetles), pinnate (butterflies, dipterans), cranked (lamella beetles) ), club-shaped (butterflies, beetles). Antennas perform tactile and olfactory functions; in various species of insects they are used to perceive temperature, air humidity, ultrasound, and the gravity of the Earth.

Types of antennas. 1. Thread-like. 2. Club-shaped. 3. Lamellar. 4. Fan-shaped. 5. Columnar. 6. Comb. 7. Bristle-like.

The mouth of insects has a different structure depending on the method of feeding. The oral apparatus is distinguished as gnawing (beetles, ants, orthoptera), lapping (bees, bumblebees), piercing (mosquitoes, bedbugs), sucking (butterflies), licking (flies). Apparently, the most primitive oral apparatus is the gnawing type. This is indicated by the presence of such a mouth in the larvae of insect orders, which in adulthood have mouthparts of other types, richly articulated appendages, and similarity with the mouthparts of centipedes (according to one hypothesis, insects descended from centipedes or have common ancestors with them). It is assumed that the primary feeding for insects was small remains of animal or plant origin, from which other types of nutrition subsequently developed. These ideas are consistent with the assumption that the gnawing oral apparatus of the greater tubercles is primitive. The oral apparatus includes the upper lip (labrum), a pair of upper and lower jaws, the lower lip and the hypopharynx (hypopharynx). The upper lip is a fold of the integument of the head, the hypopharynx (tongue, subpharynx) is a protrusion of the floor of the oral cavity. A pair of upper jaws (mandibles, or mandibles) are the limbs of segment II of the head (segment I and its appendages are almost completely reduced). These powerful, undivided plates, jagged along the outer edge, play a major role in gnawing food. In primitive insects, the upper jaws are connected to the head capsule by one joint (condyle) and are capable of moving in different planes. Their movements are less precise and forceful compared to the movements of the bicondylar maxillae of advanced insects. The latter type of jaw can only move in one plane.

Gnawing mouthparts. 1. Upper lip. 2. Mandible. 3. Subpharyngeal 4. Maxillary palp 5. Labial palp. 6.Lower lip. 7. Mouth opening 8. Antenna (antenna). 9. Eye. 10. Oral apparatus.

The upper jaws are followed by two pairs of lower jaws - the limbs of segments III and IV. Often in the literature, only the first pair is called the mandible; it is located on the sides of the oral opening. Each jaw consists of a two-segmented base and 3 appendages at its apex: the internal and external lobes and the maxillary palp. The second pair of mandibles merges and forms the lower lip: on a two-segmented base (chin + subchin) sit 2 pairs of lobes and a pair of lower labial palps. The dissected maxillary and labial palps are equipped with tactile and chemoreceptors.

The lapping mouthparts of bees and bumblebees are characterized by the elongation of both pairs of lower jaws and the formation of a proboscis, which serves to absorb nectar. The proboscis can be folded into two knees and pressed against the head with the upper jaws, or vice versa, it can move forward strongly and penetrate flowers with deep corollas. The upper lip and upper jaws are practically unchanged; the jaws are used for collecting and grinding hard flower pollen and building nests.

The piercing proboscis of mosquitoes consists of a groove and modified parts of the oral apparatus placed inside it. The groove is formed by a strongly elongated lower lip, the palps of which have been almost completely reduced. The upper lip also extends, its edges close, forming a tube for sucking blood. Between the inner surface of the groove and the tube, piercing stylets are placed, arising from the upper jaws, the first pair of lower jaws and the tongue. The cavity of the tongue serves to conduct saliva.

The piercing-sucking apparatus of the bug is formed by four stylets enclosed in a sheath - a modified lower lip. The internal pair of stylets - the first pair of mandibles - forms two grooves for conducting saliva into the wound and suctioning liquid food. The upper jaws, which make up the outer pair of stylets, alternately move out of the sheath and go deeper into the wound. Then the lower jaws simultaneously move forward. All operations are repeated until the stylets penetrate to a sufficient depth into the tissue of the feeding organism.

The oral apparatus of Lepidoptera is represented by a sucking proboscis, consisting of a pair of lower jaws tightly adjacent to each other, each of which forms a groove. The inner surfaces of the grooves form a tube for sucking nectar. In the resting state, the proboscis is curled into a spiral and hidden under the head. It unfolds due to the injection of fluid into the cavities of the lower jaws connected to the body cavity. The remaining parts of the oral apparatus are atrophied: the upper lip practically disappears, the lower one is a small plate with three-segmented palps. There are no upper jaws.

The main part of the licking mouthparts of flies is the fleshy lower lip, which ends in a pair of plate-like outgrowths. These outgrowths serve to filter semi-liquid food. At rest they are folded, and when fully unfolded they expose teeth, which are used for scraping the substrate. The upper jaws and the first pair of lower jaws are atrophied, but the mandibular palps are preserved. The upper lip and tongue lie in the recess of the lower lip and form a tube through which filtered food particles move.

Depending on the position of the mouthparts, three types of head positioning are distinguished: if the mouthparts are directed downwards, then the head is hypognathic (in cockroaches), forward – prognathic, obliquely backward – opisthognathic. The latter is characteristic of leafhoppers and aphids: the displacement of the stylets towards the center of gravity of the body facilitates the piercing of hard integuments.

The chest consists of three segments, which are called the prothorax, mesothorax, and metathorax (prothorax, mesothorax, metathorax, respectively). Each segment has a pair of limbs, and the last two have two pairs of wings.

The limbs are attached between the ventral and lateral chitinous plates (sclerites) and consist of a wide main segment - the coxa (thighs; coxa), trochanter, femur, tibia and tarsus. The coxa is attached to the body by two joints (condyles) and can move forward and upward or backward and downward. The articulation between the trochanter and the thigh allows movement in different directions, and the knee articulation between the thigh and shin is needed to bring the limb closer to the body. The tarsus consists of several segments (usually five) and ends with 1–2 claws. With their help, the insect is firmly attached to the substrate. Sometimes large bristles called spurs are located on the top of the tibia. They are involved in the movement of the limb and serve as one of the defining characteristics in some families.

Insect wings are lateral outgrowths of the body wall. They are formed by thin membranes stretched over a framework of veins through which trachea, nerves and abdominal fluid penetrate into the wing.

The veins penetrate the entire insect wing (there are especially many of them at the leading edge of the wing), providing the necessary rigidity of the structure and its aerodynamic properties. The first, thickest vein is called costal. Below it is the subcostal vein). Next come the branching radial and medial veins. Their branches are numbered and designated R 1, R 2, R 3, ..., M 1, M 2, M 3 ... They form a radius sector and a medial sector. In the posterior part of the wing there are cubital, anal and juginal veins. In addition, at the point where the subcosta meets the costa there may be a dense cuticular formation - the wing ocellus, which removes one of the harmful vibrations during flight. The movements of the wings are limited by numerous small chitinous plates located in the area of ​​the articular membrane between the dorsal and lateral plates.

Wing venation. C – costal vein, Sc – subcostal vein, R – radial vein, M – medial vein, Cu – cubital vein, An – anal vein, Ju – jugal vein.

Some of them are attached to muscles that serve to change the angle of inclination of the wings or fold them along the body. The muscles that provide wing movements in flight are usually indirectly acting muscles: their contraction causes deformation of the walls of the so-called sternopleural complex (the ventral and lateral chitinous plates merge, forming a cup-shaped capsule that gives the segment additional strength), flattening or arching of the dorsal plate , and accordingly, the movement of the wings up or down.

In various groups of insects, there is a tendency towards the functional unification of both pairs of wings or the reduction of one of them. The fore wings are well developed in lepidopteran and dipteran insects (in the case of dipterans, the second pair of wings turns into halteres - formations that serve to stabilize flight). Fanoptera, Coleoptera and Orthoptera are characterized by the predominant development of the wings of the third thoracic segment. In beetles, the first pair of wings turns into elytra (elytra), protecting the dorsal part of the body and wings. The order Hemiptera includes insects in which only halves of the elytra harden. In dragonflies, both pairs of wings are developed almost equally. Some independence of one pair of wings from the other and the presence of direct-acting muscles allow dragonflies to achieve excellent flight characteristics. Among insects there are primarily wingless forms (subclass Apterygota) and species in which wings have been reduced (lice and fleas).

The abdomen is the last section of the insect's body. Its structure is different. All 11 segments are present only in lower insects (Protura); in the rest, some of the segments are reduced (usually the last few). Higher insects have 4–5 abdominal segments.

The genital organs of insects are located on abdominal segments VIII–IX. The ovipositor of females is formed by 4–6 valves - outgrowths of ovipositor plates, which are a modification of the abdominal legs. The valves, moving relative to each other, push the egg along the ovipositor; the same mechanism is used to bury eggs in the substrate: the female makes a passage into which she then lays eggs. Some insects lay eggs in wood (horntails, sawflies). Their oviparous valves are equipped with ribs and teeth. Ichneumas, which lay eggs in the larvae of other insects, have a very long ovipositor.

The ovipositors of higher Hymenoptera turn into a poisonous sting. The bees have small serrations on their wings that help secure the stinger in the skin of the victim. Because of these notches, the bee cannot remove the sting and dies.

The copulatory organ of males, unlike the ovipositor of females, is not homologous to the limbs and consists of a base (phallobase) and a tubular aedeagus, which serves for ejaculation.

Often the abdomen bears various vestigial structures. Representatives of the order Protura have two-segmented limbs on the first three segments. The abdominal segments of bristletails have special appendages - styli, on which the abdomen of insects slides along the substrate, like on runners. Springtails carry hooks on segment II that fix the jumping fork of segment IV. When the teeth of the hook are brought together, the fork is released, strikes the substrate, and the body of the insect is thrown up.

The aquatic larvae of mayflies and flies have appendages on the first seven segments that act as tracheal gills. The three gills of dragonfly larvae are located on the last abdominal segment. Butterfly caterpillars have pseudopods – fleshy structures located on segments III–VI, X and involved in the movement of the insect’s body. A characteristic feature of many lower insects is the terminal appendages (XI segment).



Forestry

Bachelor's training

FOREST ENTOMOLOGY

Guidelines for laboratory classes and independent work of students studying in the field of

Bryansk 2012

Forest entomology. Guidelines for laboratory classes and independent work of students studying in the bachelor's degree 250100 - Forestry. The structure of insects. /Bryansk: BGITA, 2012. - 35 p.

Compiled by: Shelukho V.P.. – Doctor of Agricultural Sciences, Professor

Reviewer: Timoshenko S.G. - Head of the Bryansk branch of the Forest Protection Center of the Kaluga Region, Federal Budgetary Institution "Roslesozashchita"

Based on the experience of teaching the academic discipline, theoretical justification and methodological recommendations are provided for conducting laboratory classes and independent work of students in forest entomology to master the structure of insects as the basis for organizing measures to control the number of forest pests, which is aimed at increasing the efficiency of the educational process and the formation of certain competencies.

For the teaching staff of the Department of Forest Protection and Game Science of BGITA, for students of the Faculty of Forestry.

The transition to individually-oriented training of students is an integral part of modern methods of enhancing and improving the quality of training of competent professionals. The preparation of bachelors is based on a large amount of independent work of students, fully providing them with a variety of information resources based on information computer technologies.

This methodological guide is not only methodological instructions for conducting laboratory classes in the course of forest entomology, but also a brief methodological guide for students to independently master the most important section of entomology - the structure of insects, knowledge of which is necessary for understanding the physiology of this group of animals, understanding possible ways of influencing forest pests in order to control their numbers and harmfulness.

The forest entomology course is included in the complex of knowledge acquired by the student while studying forestry. The course consists of lectures, laboratory classes, summer internship and diploma design. Laboratory classes are conducted in the 6th semester for 28 hours. During the classes, students get acquainted with the amazing and diverse world of insects, with species useful for human economic activity, with insects harmful to forests, gain skills in identifying species, get acquainted with the biology and ecology of forest insects, with a set of measures to limit the number of pests, acquire biological skills plant protection.

Laboratory classes complement lectures and, if necessary, detail individual theoretical lecture questions.

The experience of the department shows that the forest entomology course requires a lot of attention, hard work and thoroughness from the student when completing laboratory practical tasks. It should be remembered that deep knowledge in any discipline can only be provided by a set of training sessions, which includes lectures, educational and practical training in the forest, diploma design, work in a student scientific circle, excursions to nature and to the museum.

Insects are of great importance as pests, pollinators, soil formers; many species are an adornment of nature.

The department has a good laboratory, scientific equipment, modern teaching materials, widely uses testing, and the use of a variety of electronic media. Monitoring student progress is carried out by the teacher through systematic written or oral questioning and checking notes. Knowledge of insect taxonomy is tested using factual material (insect handouts, collections, preparations, etc.).

Topic: Structure of insects

1 Introduction to the phylum classes of arthropods

Insects belong to the broad phylum of arthropods - Arthropoda. In addition to insects, it includes a variety of animals that have a hard external skeleton, divided into segments.

This type is the most numerous in the animal world. It unites over 1.5 million species (according to some estimates, 2...7 million species). Representatives of this type are very adapted to life in various environmental conditions; they play a huge role in the life of the forest and biosphere.

The phylum arthropod consists of 4 classes (Table 1). It is necessary to learn the distinctive features of these classes and indicate useful and harmful representatives. The table is written in the workbook. 1, characterizing the characteristics of these classes.

Based on the collections, signs of the external body structure of typical representatives of individual classes are considered.: woodlice, crayfish, spiders, ticks, nods, beetles, butterflies, etc.

Table 1 Type of arthropod - Arthropoda

Class insects - INSEKTA

The origin of insects is associated with the action of the process of oligomerization (reduction in the number of homogeneous structures performing the same functions) in the process of evolutionary development from a worm-like segmented ancestor (Figure 1).

This class includes six-legged arthropods, which have a complex development cycle with transformation and a body divided into 3 sections. The anterior section is the head, which contains eyes, antennae and 3 pairs of mouthparts. The next section is the chest, consisting of 3 segments, each of which usually carries a pair of legs; in flying insects, the second and third segments of the thorax also bear a pair of wings. The posterior part of the body is the abdomen. It consists of 4...11 segments and has no legs. The last segments of the abdomen usually bear modified appendages adapted for mating or for laying eggs. The exoskeleton of insects, like other arthropods, protects internal organs and maintains body shape.

With the exception of some viviparous forms, all insects lay eggs. Immature insects molt several times during their development to the adult stage and, as a rule, with each molt their body size increases and specialized organs appear.

Immature insects do not have wings. The only exception is some mayflies, in which the last short-lived immature stage already has functional wings. Immature individuals in insects with a full development cycle do not look like adults (caterpillar - butterfly) and may not have structures typical of adult insects.

Insects represent the most numerous group of animals by species. Sometimes the number of insects is so great that they form entire clouds.

Insects inhabit all types of ecosystems on the planet, with the exception of the depths of the ocean. They live in the tropics and are one of the few permanent inhabitants of the South Pole region.

Adaptive capabilities of insects

Insects are the most highly developed group of terrestrial arthropods. The mechanical advantages of the exoskeleton created the conditions for further specialization, giving them an edge over their competitors. Thanks to the presence of an exoskeleton, insects received a large surface for attaching muscles, excellent opportunities for regulating water evaporation, which is especially important for small animals, and almost complete protection of vital internal organs from external damage.

The most important features of insect specialization:

Wings. They are a product of the radical, revolutionary development of animals (the principle of aromorphosis). The ability to fly immeasurably increased insects' chances of surviving and spreading across the planet. Opportunities for feeding and reproduction have increased, and new ways of avoiding enemies have emerged. Increased opportunities for obtaining food opened the way for the use of more specific sources, especially in cases where food or breeding sites were available in limited quantities and were difficult to access.

Small sizes. The evolution of insects went in the direction of developing a large number of small individuals rather than a small number of large ones. This allowed for the use of many new and unusual types of food found in small quantities, and also created more opportunities for shelter and avoidance of enemies. The disadvantage of small sizes is that the surface of the body is disproportionately large compared to its volume. This greatly increases evaporation and makes terrestrial life almost impossible for animals with thin body coverings. The acquired sclerotized cuticular exoskeleton of insects provides them with the regulation of evaporation, which allows them to be small in size.

Complete metamorphosis. The life cycle of insects consists of 4 stages: 1) egg; 2) larva, or feeding stage; 3) pupa, or resting transitional stage; 4) adult insect, or reproductive stage (imago). This type of life cycle is found in the groups of insects with the largest number of species, including beetles and flies. In almost all insects with this type of life cycle, growth occurs only through larval feeding. In an adult insect, the food consumed is mainly spent on the maturation of reproductive products. Different life tasks allow larvae and adults to live in completely different habitats with different living conditions, since the living conditions of the larvae must be favorable for rapid growth, and the living conditions of the adult must be favorable for mating and dispersal. Complete metamorphosis gave insects access to a huge variety of habitats and food types, which led to the development of complex types of behavior. Complete metamorphosis allows a species to take advantage of two completely different habitat types while avoiding many of their negative aspects.

Complete metamorphosis is absent in almost half of the orders, but they develop other adaptive features.

Increase in the number of species. The main reasons, from the point of view of the theory of evolution, that led to such species diversity of insects are as follows:

1. Many species of insects are adapted to life only within the narrow limits of certain environmental factors, such as hosts, temperature, humidity. With relatively small but long-term climate changes, as occurred during the Ice Age, the range of such species is divided into isolated parts.

2. Thanks to the ability to fly, winged insects can move long distances, overcoming water and other obstacles with air masses. As a result of such movements, insect populations can colonize new habitats that are geographically isolated from the habitats of the main populations of the species. Such colonizing populations can develop into new species.

3. Genetic incompatibility between isolated populations, expressed in the impossibility of mating and development of offspring, can occur very quickly in insects due to the short life span of one generation and lead to accelerated speciation.

2 Sections of the body, their structure, functions and appendages

2.1 Division of the insect’s body into sections:

head, chest, abdomen and their appendages

Explanation for the task

The outer integument of insects is a hard exoskeleton, which serves as a support for the attachment of internal muscles and gives rigidity to the insect's body. The body wall can be quite flexible or elastic, but it is capable of stretching only for a short time after molting. The relative flexibility of the body is ensured by dividing it into separate segments - segments that are connected to each other using elastic membranes.

Merging with each other, the segments form 3 sections: head, chest and abdomen. Using the example of a black cockroach or a cockchafer, it is most convenient to distinguish between these sections. Each of the sections bears appendages for various purposes (Figure 2).

The order of dismemberment of the insect body

The student independently dismembers the body of the cockchafer into 3 sections: head, chest and abdomen.

The following sequence is followed in the work: the beetle is placed on its back on a glass slide and held in this position with a dissecting needle. The head is separated along the border of the head and chest with a scalpel. Then the abdomen is separated, for which the cutting line with a scalpel should be drawn immediately behind the third pair of legs.

The remaining section of the chest is divided into its 3 constituent segments as follows: an incision is made behind the first pair of legs, after which the prothorax is easily separated. Then an injection is made with a needle into the apex of the scutum (the triangle at the base of the elytra), the elytra are spread apart and the second thoracic segment (mesothorax) with the second pair of legs associated with it is separated from the ventral side with a scalpel. This segment is very narrow, and the cutting line with a scalpel should pass immediately behind the second pair of legs. The third segment remains on the glass plate - the metathorax. One pair of wings are attached to the mesothorax and metathorax on the dorsal side, and one pair of legs on the ventral side.

The insect dissected in this way is laid out on glass in the order of successive body parts.

Considering the head section, it is necessary to establish its shape and position in the following insects: large pine weevil, dead bark beetle, grasshopper, ground beetle. The structure of the head capsule is illustrated using the example of the cockchafer. Depending on the method of attachment of the head, the main prognathic and hypognathic types are distinguished (Figure 3).

2.2 Head and head appendages

The head capsule serves to house the brain (peripharyngeal nerve ring) and appendages. The capsule is formed by the fusion of head segments (5...6 pieces) and is durable. The six trunk segments, which merged with the ancestral head region, or acron, and became part of the current complex single structure we call the head, bore paired appendages.

Like other segmental appendages belonging to the rest of the insect's body, the head appendages evolved from simple legs typical of primitive arthropods. Such a prototype was probably the leg of trilobites. The parts of the head are named by analogy with the parts of the human head (Figure 4).

Platband(clypeus). This area resembles a lip and lies between the frontoclypeal suture and the upper lip under the eyes in the anterior part of the head capsule. The clypeus is fused with the forehead.

Forehead. This area is located at the lower front of the face above the clypeus and is limited laterally by the frontal sutures.

Cheeks. The cheeks are the lower part of the head below the eyes and behind the forehead. Sometimes there is a buccal suture in front of the front part between the forehead and cheeks; if this seam is absent, then there is no definite boundary between the cheeks and forehead.

crown. The area at the back of the head above the eyes.

Back of the head. This area covers most of the back of the head. It is separated from the crown and cheeks by the occipital suture.

Back of the head. This is a narrow ring-shaped sclerite that forms the edge of the foramen magnum. It is separated from the back of the head by the occipital suture, which is present in almost all adult insects. The occiput bears the occipital condyles, with the help of which the head is attached to the cervical sclerites of the cervical region.

Foramen magnum, through which the esophagus, nerve cord, ducts of the salivary glands, aorta, trachea and free blood pass. Inside the head is a complex of crossbars called the tentorium.

Exercise

The individual parts of the head capsule (sclerites) are examined through a magnifying glass: clypeus, forehead, crown, cheeks, temples, occiput, throat, neck. Antennae, eyes, mouth opening and mouthparts are searched (Figure 4).

Head capsule appendages and oral apparatus.

Head insects bear antennae, eyes and mouthparts.

2.2.1 Structure and types of mouthparts

The three most important parts of the oral apparatus are the upper jaws (mandibles), the lower jaws (maxillae) and the lower lip (labium). All of them are the result of modification of the typical paired limbs of arthropods.

Evolutionarily, it turned out that ancestors and ancient insects ate solid food - dead vegetation, therefore the primary oral apparatus is of the gnawing type. All other types of mouthparts appeared in the process of evolution as an adaptation to changes in food and methods of obtaining it. Three pairs of limbs of insect ancestors were used to construct parts of the mouthparts.

Upper lip. In a typical case, it is a movable visor hanging from the edge of the casing and covering the mouth. The upper lip was formed by separating the facial part of the head from the supraoral shield. The shape varies significantly among different insects.

Upper jaws (mandibles, mandibles). They are modified paired appendages of the 4th segment of the head capsule. Typically, they are hard, highly sclerotized, have teeth of various configurations and are designed for biting off large particles of food. In insects that feed on liquid food lying on the surface, they are reduced.

Mandibles (maxilla). They are located directly behind the mandibles and are paired appendages of the 5th cephalic segment. They have only lateral articulation with the base of the head capsule. Designed for grinding large pieces of food, they have a segmented structure and bear palps with chemical sense organs placed on them. The lower jaws of insects with a sucking type of mouthparts have formed a sucking tube (butterflies) due to the mandibular palps.

Underlip. The articulated formation, which represents partially fused paired appendages of the 6th head segment, closes the oral cavity from below. It appears to be a single element, but consists of a second pair of maxillae (lower jaws) that are fused along the midline to form a functionally unified structure. Parts of the lower lip correspond to parts of the lower jaws. In insects with a gnawing-licking type of mouthparts, parts of the lower lip lengthened and formed a lapping tongue (bees), and in species with a piercing-sucking type (mosquitoes, bedbugs) - a proboscis. With the piercing-sucking type of apparatus, all parts of the original gnawing apparatus are greatly elongated and serve to pierce (cut through) tissues and serve as a cover for the lower labial proboscis. Bedbugs have a joint on their mouthparts that allows them to rest their proboscis on their chest.

Procedure for completing the task:

1. The gnawing oral apparatus is dismembered into its component parts. For this purpose, the head of a previously dissected cockchafer is used. Through the occipital foramen, the head is attached to a dissecting needle. Using a scalpel, incisions are made in the area of ​​the right and left cheeks and the lower lip, bearing the lower labial tentacles and chewing blades, is separated. Then the lower jaws with tentacles, upper jaws and upper lip are separated. The selected parts of the oral apparatus are examined through a magnifying glass. The gnawing mouthparts of other insects in the adult stage and in the larvae of beetles, black cockroaches, dragonflies, etc. are also considered.

2. Having become familiar with the structure of the gnawing type (main), one should consider the structure of the piercing-sucking mouthparts. For this purpose, large bugs are used: the harmful bug, the berry bug, the pine subbark bug, mosquitoes, etc. Having separated the head, you should consider the structure of the “proboscis” and its individual bristles. It is more convenient to observe the interaction of oral parts during food intake in living insects and their larvae.

3. Consider the structure of the proboscis types of mouthparts: gnawing-licking in honey bees and bumblebees, sucking in hawkmoth butterflies, lemongrass, cabbage butterflies, etc.; piercing-sucking - in bedbugs and mosquitoes.

4. Determine the types of mouthparts of other insects offered in the set.

5. Draw the main types of mouthparts (Figures 5.6.7.8).

Material and equipment: severed heads of cockchafers, pre-steamed; set of insects in the collection: white butterflies, pine hawk moth, grasshopper, ground beetle, sorrel bug, bee or bumblebee, stag beetle. Binocular microscopes. Magnifying glasses, glass plates for dissection, dissecting needles.

2.2.2 Structure of antennae

Explanation for the task

Typically, in adult insects, the antennae are a pair of movable, jointed appendages extending from the facial surface, usually between the eyes. The main function of the antennae is to serve as the location of the sensilla (sensitive elements) of the chemical sense. The first segment is called the scape (main), the second - the pedicellum (stem), and all the remaining segments together - the flagellum (flagellum). The antenna is attached in the antennal fossa, sometimes surrounded by a narrow ring-shaped antennal sclerite. In embryogenesis, the antennae develop from the appendages of the 2nd cephalic segment. Antennae are extremely varied in shape, and some of the most clearly defined types have special names. In larvae, the antennae, as a rule, are greatly reduced both in terms of length and in terms of the number of segments. The shape and structure of the antennae are used in the taxonomy of insects to distinguish large units - families (lamellae, longhorned beetles, etc.).

The main types of antennae are shown in Figure 9. The head capsule also bears two types of visual structures: compound eyes and simple ocelli.

Exercise

1. Determine the location of the sclerites of the head capsule in the cockchafer. To do this, attach the insect's head through the occipital foramen to a dissecting needle and rotate it, holding it in this way. Examine the forehead, crown, back of the head, platbands, temples, cheeks, as well as antennae, eyes, ocelli, oral opening, and oral extremities through a magnifying glass.

2. Consider the shape and position of the head of the insects offered in the collection. Identify the types of head capsule.

3. Draw the structure of the head capsule.

4. Consider the types of antennae in various insects, determine the sex of insects by differences in the structure of the antennae of females and males.

5. Sketch the types of antennae.

Materials and equipment: a set of insects in collections or on plates - grasshoppers, elephants, cicadas, ground beetles, longhorned beetles, silkworm butterflies (females and males), cockchafer, horsefly; magnifiers 10 x, binocular microscopes.

2.3 The structure of the chest and its appendages

Explanation for the task

The chest, consisting of 3 segments (antero-, mid- and meta-thorax), bears on the ventral (lower) side one pair of jointed legs, and on the dorsal (upper) side on the 2nd and 3rd thoracic segments there are 2 pairs of wings or their rudiments.

Insect legs, consisting of several segments, and wings are appendages of the thorax.

The chest is the part of the body that lies between the head and abdomen. It consists of three sequentially located segments. Each segment of the insect's body is a chitinous ring. The chitinous plates (sclerites) that form this ring are called: dorsal, superior or dorsal plates forming a semiring - tergites; lower or ventral - sternites and 2 side walls – barrels – pleurites(Figure 10).

The tergites of the 3 thoracic sections are called sequentially: proto-, meta- and meso-dorsum, and the sternites, respectively: pro-, meso- and metathorax.

Figure 2 - External structure of the insect (dismembered stag beetle, male; (according to V.F. Natali, 1968):

1 - lower lip; 2,3 - lower and upper jaws; 4- upper lip; 5 - platband; 6 - mustache; 7 - head; 8 - prothorax; 9 - front legs; 10 - mesothorax; 11 - elytra; 12 - middle legs ; 13 - metathorax; 14 - wings; 15 - hind legs ( A- coxae, b - trochanters; V- hips; g - shins; d - paw); 16 - abdomen.

Figure 5 - Mouthparts of insects. A - gnawing type mouthparts (cockroaches); B - oral apparatus of the gnawing-sucking type (bees); IN - oral apparatus of sucking type (butterflies); G - piercing-sucking type mouthparts (bug); D - oral apparatus of the piercing-sucking type (female mosquito); E - sucking type mouthparts (male mosquito): I - upper lip; II- upper jaws, or mandibles; III - mandibles; IV- underlip; V- subpharyngeal; 1 - pendants (cardo), 2 - column (stines), 3 – outer blade, 4 - internal lobe, 5 - palp, 6 - prechin, 7 - chin, 8 - internal blades, 9 - external blades, 10 – palp of lower lip

Figure 6 - Mouthparts of the gnawing type (black cockroach) (from the book by Bogdanov-Katkov). I - upper lip; II - upper jaws; III – lower jaws; IV - lower lip: very good- main segment, stv – stem, nl - outdoor, ow - internal chewing blade, hch- maxillary palp, gsh– labial palp, ppb - chin, pb - false chin. language- tongue, paz- accessory uvula

Figure 7 - Head from below with sucking mouthparts of a butterfly (A) and piercing-sucking - bug (B) (according to Kuznetsov and Bey-Bienko and Skorikova): hob- proboscis, gsh- labial palp, vg - upper lip, HF- upper pair of piercing setae (upper jaws), LF- their bottom pair, ng- underlip, mustache- mustache, ch- eyes, glk - eyes, forehead - forehead

Figure 8 - Mouthparts of a bumblebee (according to Kholodkovsky): 1 - top lip, 2 - upper jaws, 3 - lower jaws (och - main segment, st - trunk ik, asl - chewing blades, sch- rudiment of palp); 4 - lower lip; ppb - false chin, pb - prementum, language- tongue, nl - rudiment of external chewing blades, gsh - labial palp)

Figure 9 - Types of insect antennae (according to Bogdanov-Katkov): 1 - bristle-like antennae, 2 - filiform, 3 - clearly visible, 4 - sawtooth, 5 - comb, 6 - club-shaped, 7 - fusiform, 8 - lamellar, 9 - cranked, 10 - feathery, 11 - bristle-bearing

Parts of the antenna: 1 – main segment; 2 – stem; 3 – flagellum; 4 - antennal cavity.

Figure 10 - Diagram of the structure of the thoracic segment of an insect. A - general view; B- cross-section (according to Obenberger and Snodgrass): joint venture- back, pl- playrite, gr - breast, ptz - pretoxin (subcox), TZ - basin, b - hip, G - shin, l- paw, ax - axillary sclerites, cr- wing, pls-pleural column; internal skeleton; plch - pleural ridge, truck- furka

Figure 11 - Structure and types of legs (according to Bey-Bienko, Bogdanov-Katkov):

1 - running (ground beetles), technical specifications - basin, V - trochanter, b - thigh, g - lower leg l - tarsus, 2 - jumping (locusts), 3 - digging (mole crickets), 4 - swimming (swimmer), 5 - grasping (mantis), 6 - foraging (honey bee)

In those orders where wings never develop, these 3 segments are structured approximately identically in their main features. The tergite and sternite are plate-shaped, and the pleural sclerites are small or underdeveloped.

In representatives of winged insects, the 3 thoracic segments differ greatly from each other. The prothorax usually retains all the same parts as in its original state. The mesothorax and metathorax have undergone significant changes associated with the development in each of these segments of the muscles that provide the work of the legs and wings. The pleurite expanded significantly, forming a large side plate. From the lower part it bears a coxal process, to which the leg is attached, and from the upper part, a wing process (pleural column), to which the wing is attached. Posteriorly and anteriorly, pleurite is fused with sternite, and areas of fusion form bridges in front and behind the coxal cavities.

The sternite, uniting with the pleurite with its front and rear parts, which look like stripes, forms a depression in which the basin is located.

A typical representative of the class Insects are Khrushchev May (Melolontha melolontha). The body length reaches from 5 to 60 mm, the wingspan does not exceed four centimeters.

Features of the external structure

Body parts - head, chest and abdomen, each of which performs its own functions. Chairman formed from 6 segments that completely merge. The head has antennae, eyes and mouthparts. The antennae, which are called antennae or siblings, are one pair. In beetles they are lamellar and perform the function of an olfactory organ. The mouth has three pairs of organs: upper jaws (mandibles), lower jaws (maxilla) and upper and lower lips. These organs form gnawing mouthparts. There are projections on the lower jaws and lower lip - palps, which serve as organs of touch and taste. Along with the antennae there are complex (faceted) eyes. In insects they can be simple or complex.

Depending on the type of food, the mouthparts of insects are modified, which leads to the formation of different types of mouthparts:

gnawing mouthparts - oral organs, which include upper And lower lips, upper And mandibles(e.g. grannies, beetles, cockroaches, orthoptera, termites, ants)

gnawing-licking oral apparatus- oral organs in which the lower lip and lower jaws form proboscis, A upper jaws lost chewing function and participate in the construction of honeycombs (bees, bumblebees)

sucking mouthparts - mouth organs have been transformed into proboscis, which is adapted to feeding on nectar from flowers (butterflies)

piercing-sucking mouthparts- oral organs in which the lower lip forms proboscis for sucking liquids, and the upper and lower jaws are turned into long, spiny ones stilettos for piercing body coverings (bugs, aphids, lice, some dipterans).

Some adult insects (silkworms, gadflies) do not feed, so their mouthparts do not function and are very reduced.

Thoracic region consists of three segments (prothorax, mesothorax and metathorax), which have organs of movement - legs and in winged insects - wings. On each segment of the chest there is one pair of limbs, and therefore in insects 3 pairs of walking legs, which is why they are also called hexapods (six-legged). In other insects, these limbs can perform other functions and therefore the following types are distinguished: jumping, swimming, grasping, digging, running, and the like. Two pairs of wings are attached to the second and third segments of insects. Wings are folds of integument, the walls of which are built from the upper and lower layers of epithelial cells covered with a cuticle. Between these layers there is a gap with hemolymph. The supporting frame of the wing is formed by a system of longitudinal and transverse thickenings called veins. In beetles, the first pair is modified into hard elytra. Elytra- modified fore wings that protect the membranous wings from damage when the insect is not flying.

Abdomen formed by a different number of segments (no more than twelve) and contains the bulk of the internal organs. This section is devoid of limbs, has openings of the tracheal system - spiracles, and ends with an ovipositor.

Veils are represented by the hypodermis and chitinous cuticle with a waxy film that prevents the evaporation of water. On the body of an insect there are numerous hairs that perform the function of organs of touch, create an air layer that protects the body from water during rain, from overheating, determine coloring, and the like. Ducts of odorous glands open onto the surface of the body, which help individuals find each other during reproduction. In other insects there may be poisonous (in hairy caterpillars), wax (in bees), silk (in butterfly larvae) and other glands.

Features of the internal structure and life processes

Digestive system consists of the anterior (oral cavity with salivary glands, pharynx, esophagus, stomach), middle (midgut with pyloric appendages, without liver) and posterior (hindgut with anus) sections. Khrushchev eats plant foods, so the outgrowths of its intestines contain symbiotic microorganisms that secrete enzymes for digesting fiber. In larvae, the intestine is relatively long and food remains in the body for a long time. Absorption of water in order to prevent its loss occurs in the hindgut with the help of the rectal glands.

Respiratory system - tracheal type. A system of tracheal tubes branches throughout the body, which open on the abdomen with dichals - stigmas (on one segment - a pair). Air moves in this system due to diffusion and abdominal movements.

Circulatory system open The heart is tubular, located in the dorsal part of the abdomen.

System fluid - hemolymph- colorless and does not participate in the transportation of gases, which is associated with the development of the trachea. It performs functions such as transport of nutrients

Internal structure of the May beetle: A - antennae; B - subpharyngeal nerve ring: B - December ganglia; G - trachea; D - heart; E - ovary; F - Malpighian vessels; WITH - spiracle; AND - goiter; AND - stomach

substances, transfer of metabolic products, distribution of hormones, protection with the help of phagocyte cells from microorganisms, etc. Hemolymph circulation is carried out by contractions of the heart. When the walls of the heart are stretched with the help of muscles, hemolymph enters the heart through the lateral openings (ostia), and when contracted, the valves close the ostia and fluid enters the arteries.

Excretory system represented by Malpighian vessels and the fatty body. Malpighian vessels are excretory tubes at the border of the midgut and hindgut. The number of these outgrowths varies from 2 to 150. The fat body is loose connective tissue, which, among other functions, absorbs metabolic products.

Nervous system - nodal chain type, which is characterized by a well-developed “brain” - a suprapharyngeal accumulation of neurons. It is divided into C sections - anterior, middle and posterior. The anterior section is more complex and provides complex forms of behavior. The ventral chain consists of the pidpharyngeal ganglion and, as a rule, 10 thoracic and abdominal enlarged ganglia.

Behavior very complex and is determined by the interaction of unconditioned and conditioned reflexes. Such innate forms of behavior as instincts play a big role for insects.

Endocrine system carries out humoral regulation with the help of hormones that are secreted by the suprapharyngeal and subpharyngeal nodes, brain appendages, etc. Biologically active substances such as ecdysone, that affect shedding, " juvenile hormone"- inhibits maturation pheromones influence members of their own species sex attractants- attract individuals of the opposite sex during reproduction, etc.

Sense organs - the most diverse, which is associated with the general high level of organization and complex behavior of insects. Basically, these are hair or other creations with a receptor inside: organs of vision - eyes, complex faceted and simple, organs of smell - antennae, organs of taste - on the mouth and other parts of the body, organs of touch - sensitive hairs on the integument of the body, hearing organs ( tympanic organs, chordotonal organs) are located on the abdomen (in grasshoppers - on the legs). In May beetles, as in other flying insects, there are special antennae at the base. Johnston bodies to control the speed and direction of flight.

Reproduction. May beetles, like almost all insects, are dioecious. Fertilization is internal. The sexual dimorphism of the May beetle is expressed in the fact that the antennae of males have seven segments, while females have only six; females have an ovipositor for laying eggs, extended shin legs for burying them in the soil, etc.

Development in the May beetle it is indirect, in which a pupa is observed in the life cycle. Doll - a stage of insect development with complete metamorphosis, in which internal restructuring occurs, as a result of which the insect turns from a larva into an adult. The transformation from egg to adult insect stage is regulated by hormones and continues for several years in the beetle.

Development in most insects is usually indirect, but there is direct:

1) straight (in primary insects without wings, or bristletail)

2) indirect (or development with transformation - metamorphosis):

■ with complete transformation: egg - larva - doll - imago (in Coleoptera, Hymenoptera, Lepidoptera, Diptera, fleas)

■ with incomplete transformation: egg - larva - imago (in Orthoptera, cockroaches, bedbugs).

The biological significance of the transformation is that: a) larvae and adults live in different conditions and therefore do not compete for habitat and food; b) insects have a greater opportunity to survive under unfavorable living conditions (low temperature, lack of food) at one or another less vulnerable stage of development, in general promotes an increase in the number of individuals of the species.