What appears in insects from eggs. Types of insect development

Insects with incomplete metamorphosis

The cockroach, like representatives of some other orders of insects ( Mayflies, Dragonflies, Mantises, Stoneflies, Orthoptera, Earwigs, Lice, Homoptera), development occurs with incomplete transformation . This means that larvae emerge from the eggs - small insects that look very similar to their parents. They differ from adult insects in their smaller size, lack of wings and underdeveloped reproductive system. The larvae molt several times, grow with each molt and become more and more like adult insects. Over time, they become sexually mature and their wings are fully formed. After this, the insects no longer grow.

Thus, an insect with incomplete metamorphosis goes through three stages in its development: egg -> larva -> adult insect (Fig. 101).

Dragonflies. A order of well-known insects with a long slender body and two pairs of strong transparent wings (Fig. 102, 1 ). Dragonflies (especially large ones) are distinguished by very fast and maneuverable flight. They are predators, catching insects (flies, mosquitoes, small butterflies) on the fly. Dragonflies have large compound eyes that provide nearly all-round vision and long legs lined with coarse hairs. Dragonfly larvae are inactive and live in ponds, lakes, ditches with water, and slowly flowing rivers. They are also predators and grab passing crustaceans, larvae of other insects, tadpoles and fish fry with the help of a lower lip capable of being thrown forward, which is called mask .

Orthoptera. This group includes locusts, grasshoppers(Fig. 102, 3 ), crickets And mole crickets. They have two pairs of wings (the front ones are denser than the hind ones), many have jumping hind limbs, and a gnawing mouthparts. Many of the Orthoptera jump in heights of up to 80 cm, and if they help themselves with their wings, the distance they cover in one jump reaches 10 m. Some types of locusts fly well. Locusts feed on plants, grasshoppers are both herbivores and carnivores, and crickets are omnivores.

Homoptera. This group belongs to cicadas(Fig. 102, 6 ) And aphids. Their mouthparts are of the piercing-sucking type, and their wings are usually folded into a roof. Homoptera feed on plant sap. Cicadas are fairly large (up to 7 cm long) diurnal insects and are known for being able to produce very loud sounds using special organs located at the base of the abdomen. Aphids – small insects several millimeters long. Among them there are both winged and wingless forms.

Bedbugs, or Hemiptera. Insects of this order are so called because their fore wings (elytra) are dense in front and soft in back (Fig. 102, 2 ). The second pair of wings lies under the first. It is with the help of the second pair of wings that bedbugs can fly. Some, for example bed bug , wings are missing. The mouthparts of bedbugs are piercing-sucking. Among bugs there are species that feed on plant juices, there are predators and bloodsuckers (bed bugs).

Insects with complete metamorphosis

In insects with complete metamorphosis, the larvae do not at all resemble adults. These are the larvae butterflies, beetles, flies, wasps, ants. These larvae lack compound eyes, have only simple ocelli, or have no visual organs at all; the body is most often worm-shaped (butterfly caterpillars). Often there are no antennae and no wings. Insect larvae with complete metamorphosis molt several times and grow. Having reached its maximum size, the larva turns into doll - This is another stage of development, usually motionless, intermediate between the larva and the adult insect.

Thus, insects with complete transformation go through four stages in their development: egg -> larva -> doll -> adult insect (Fig. 103).

In insects with complete metamorphosis, the larvae often live in completely different places and feed on different foods than adult animals. So, caterpillars (butterfly larvae) feed on green parts of plants, their mouthparts are gnawing. Adult butterflies feed on the nectar of flowers, and their mouthparts are sucking. Midges suck the blood of mammals, and their larvae live in running water of rivers and catch small organic particles carried by the current. The difference in habitats and nutrition of insects at different stages of development with complete transformation eliminates competition between larvae and adults of the same species.

Most species of insects are characterized by development with complete transformation.

Butterflies, or Lepidoptera(Fig. 104, A). Insects of this order are so named because they have very small chitinous scales on their wings. They are variously colored and strongly refract the incident light. That's why butterfly wings have fancy and bright colors. The coloring of the wings of butterflies helps them recognize each other, camouflages them in the grass and on the bark of trees, or warns enemies that the butterfly is inedible. The sucking mouthparts of butterflies are a proboscis coiled into a spiral. Butterflies feed on the nectar of flowers. When pupating, the caterpillars of some butterflies secrete silk threads. Threads mulberry And oak silkworm people use it to produce silk fabrics.

Beetles, or Coleoptera(Fig. 104, B). Representatives of this order have dense, hard elytra that cover the second pair of leathery wings, with the help of which they fly. The mouthparts are gnawing. Among the beetles there are many herbivores. There are also predators that hunt other insects and carrion eaters. Beetles live in ground-air environment(on plants, the surface of the earth, in the soil) and in water. Beetle larvae are both very mobile predators, living openly, and sedentary, worm-like, living in shelters and feeding on plants, fungi, and sometimes decomposing remains of organisms.

Diptera(Fig. 104, IN). These insects have only one pair of wings. The second pair is greatly reduced and serves to stabilize the flight. This group includes mosquitoes And flies. Some dipterans have a licking mouthparts, while others have a piercing-sucking mouthparts. Among the dipterans there are those that feed on pollen and nectar of flowers (syrphid flies), predators (ktyri) and bloodsuckers (mosquitoes, midges, midges, horseflies). Their larvae live in the decaying remains of cesspools and composts (house flies), in water (mosquitoes And midges) or lead a wandering lifestyle and hunt small insects.

Hymenoptera(Fig. 104, G). The order includes such well-known insects as bumblebees, wasps, bees, ants. Representatives of this order have two pairs of membranous wings, but some have no wings. This group belongs to sawflies. They are called so because the females have a serrated ovipositor that resembles a saw. With this ovipositor, females cut leaves and stems of plants, and then lay eggs there. Sawfly larvae are similar to butterfly caterpillars. Hymenoptera include riders. Their females, using a long ovipositor, pierce the covers of the caterpillars and lay eggs in them. The larvae emerging from the eggs eat the caterpillars.

Not complete transformation: egg -> larva -> adult insect (orders Dragonflies, Orthoptera, Homoptera, Bugs); complete transformation: egg -> larva ->doll -> adult insect (orders Lepidoptera, Coleoptera, Diptera, Hymenoptera).

Insects are a class of invertebrate arthropods, 1.5 million species. The body is covered with a chitinized cuticle, forming an exoskeleton, and consists of three sections: head, thorax and abdomen. Habitat: ground-air; water; soil; organismic. From mm to 15 cm – body length. On the head: a pair of antennae; oral organs (lower, upper jaws, lower lip); a pair of compound eyes; mustache different shapes; oral apparatus (gnawing, piercing-sucking, sucking, licking-gnawing). Chest: two pairs of wings (1 pair - on the mesothorax, 2 pairs - on the metathorax); three pairs of walking limbs (running, jumping, swimming, grasping, digging). The wings are folds of chitinous cover. Abdomen: has no limbs, sometimes there may be modified limbs (cerci, grasshoppers). Sense organs: touch - antennae; sense of smell - antennae; taste – palps of the lower lip and lower jaw; vision – simple and compound eyes; hearing; balance.

Insects are higher invertebrates.

The class has more than 1 million species.

Habitat: soil, air-ground, organisms of other living beings

The body is divided into sections: head, chest, abdomen.

The thoracic region consists of three segments; each carries one pair of legs. Consequently, insects are characterized by the presence of 3 pairs of limbs. The second and third segments, in addition, can carry a pair of wings. In some insects, both pairs of wings are well developed, but wingless insects are also known. The abdomen consists of 6–12 segments. The type of complex oral apparatus of insects is determined by the method of feeding and can be gnawing (beetles), sucking (butterflies), piercing-sucking (lice), licking (flies).

Body coverings and muscular system: have a chitinized cover, under which lies a single-layer hypodermal epithelium. The skin is rich in various glands: odorous, waxy, molting, etc. The muscles are transversely striated.

Digestive system: mouth, pharynx, esophagus, crop, stomach, midgut, hindgut ending in the anus. There are salivary glands and a gland that performs the functions of the liver and pancreas. Digestion and absorption of food occurs in the midgut.

Respiratory system: trachea.

Excretory organs: Malpighian vessels and fat body.

Circulatory organs: the circulatory system is not closed, the tubular heart and aorta are located on the dorsal side. Due to the fact that there is an extensive network of tracheas, the circulatory system is poorly developed and lacks the function of an oxygen carrier. Hemolymph circulates through the vessels.

Nervous system: abdominal nerve chain with a strong tendency to concentrate ganglia in the head section, so the suprapharyngeal ganglion is transformed into a “brain”, which has three sections (anterior, middle, posterior). There are sense organs: eyes (faceted, but can also be simple), balance, taste, touch and smell, and in some, hearing.

Reproductive system: insects are dioecious, sexual dimorphism is often pronounced. Gonads are paired (females have ovaries, males have testes). Sexual reproduction: with fertilization or parthenogenetic. Development is not direct: with complete metamorphosis (stages: egg - larva - pupa - adult) or incomplete metamorphosis (stages: egg - larva - adult).

The practical importance of insects is very great: pollinators of flowering plants, participate in soil formation processes, etc.

22 .Methods of sexual reproduction

There are two ways of sexual reproduction - bisexual when, during mating, the female's eggs are fertilized by the male's sperm, and virgin when an egg develops without fertilization ( parthenogenesis ).

Parthenogenesis originated from bisexual reproduction as a simplification of it and is observed in aphids and other insects. It represents a very beneficial device, allowing insects to quickly increase their numbers and spread throughout the territory. Parthenogenesis is diverse in its manifestations. Thus, in the honey bee, males (drones) develop from unfertilized eggs, and females (worker bees and queens) develop from fertilized eggs. In a number of insects, a regular alternation of bisexual and multiple parthenogenetic generations is observed. Thus, in many gall moths two generations alternate: the summer generation, winged, bisexual, and the autumn generation, wingless, consisting only of females. Alternation of generations (heterogony) is even more complex in aphids.

One of the forms of parthenogenesis is pedogenesis or baby breeding e. In this case, parthenogenetic development of eggs occurs in the ovaries of the larvae, from which larvae emerge. This reproduction is repeated for several generations and then gives way to a series of bisexual generations with an adult phase. It is observed in gall midges and certain species of beetles and bugs.

Ichneumoceles sometimes crush an egg laid in another insect. As a result, not one, but many (up to 100) ichneumon species develop in the “host’s” body. This method of reproduction is called polyembryony .

Sometimes blood-sucking flies and other insects exhibit live birth . In this case, instead of laying eggs, larvae are produced.

In all insects, development is indirect; transformation can be complete or incomplete.

Incomplete: There is no pupal stage. Characteristic of grasshoppers, cockroaches, dragonflies.

In the cockroach, as in representatives of some other groups of insects (mayflies, dragonflies, mantises, stoneflies, orthoptera, earwigs, lice, homoptera), development occurs with incomplete transformation. This means that larvae emerge from the eggs - small insects that look very similar to their parents. They differ from adult insects in their smaller size, lack of wings and underdeveloped reproductive system. The larvae molt several times, grow with each molt and become more and more like adult insects. Over time, they become sexually mature and their wings are fully formed. After this, the insects no longer grow.

Thus, an insect with incomplete metamorphosis goes through three stages in its development: egg >> larva >> adult insect

Complete: a larva develops from an egg, it feeds, grows, then turns into a resting pupa, inside which a complete restructuring of all organs occurs, and an adult insect (imago) emerges from the pupa. Characteristic of butterflies, beetles, mosquitoes.

In insects with complete metamorphosis, the larvae are completely different from the adults. These are the larvae of butterflies, beetles, flies, wasps, and ants. These larvae lack compound eyes, have only simple ocelli, or have no visual organs at all; the body is most often worm-shaped (butterfly caterpillars). Often there are no antennae and no wings. Insect larvae with complete metamorphosis molt several times and grow. Having reached its maximum size, the larva turns into a pupa - this is another stage of development, usually motionless, intermediate between the larva and the adult insect.

Thus, insects with complete transformation go through four stages in their development: egg >> larva >> pupa >> adult insect

In insects with complete metamorphosis, the larvae often live in completely different places and feed on different foods than adult animals. Thus, caterpillars (butterfly larvae) feed on green parts of plants and have gnawing mouthparts. Adult butterflies feed on the nectar of flowers, and their mouthparts are sucking. Midges suck the blood of mammals, and their larvae live in running water of rivers and catch small organic particles carried by the current. The difference in habitats and nutrition of adult insects and their larvae eliminates competition between different stages of the same species. Most species of insects are characterized by development with complete transformation.

To produce offspring, most insects need to mate with an individual of the opposite sex. Thanks to instinctive reactions to specific smells, colors and sounds, the insect finds a suitable partner. This mechanism works in the dark, in dense thickets and over long distances. The fireflies we know do this: wingless females attract males on warm spring evenings with the help of light signals. Other insects give sound “mating” signals: for example, crickets and grasshoppers charm their partners with their chirping.

Where do insects lay eggs?

Insect eggs are usually covered with a durable shell. The stick insect simply leaves them on the ground or rolls them in front of itself. However, most females look for a place for their eggs that is protected from the wind and enemies. The insect instinctively senses in what environment the offspring, after hatching, will find favorable conditions and receive the necessary food. Crickets and grasshoppers dig holes in the ground where they place their eggs. Female mosquitoes leave eggs on the surface of the water. Butterflies and other insects whose larvae are herbivores lay eggs on plants.

Dung beetles bury mammal dung in the ground. Many of the 7,000 species of pillmakers make balls of dung by rolling them from the dung heap and burying them in safe place. They feed themselves with these balls, and also supply their offspring with “pills”. For this purpose, they make a hole in the ball and lay eggs there. The hatched larva feeds on such a ball.

Grasshoppers and ichneumon wasps have a long ovipositor, with which they pierce the soil and lay eggs there.

Growths

Some species of wasps lay eggs on oak trees and rose leaves. Gradually they are covered plant tissue. The hatched larvae feed on the creatures inside the growth, grow and pupate. Some species of mosquitoes, flies, aphids, beetles and butterflies also use plants as a “host” to breed. In order for growths to form, the plant tissue must be able to grow when the insect eggs are laid.

How do insects take care of their young?

Some types of insects care about more than just a suitable place for their offspring to hatch. Cockroaches often carry eggs with them in a kind of “bag” on the back of their body. In some species of water bugs, the female lays eggs on the back of the male. He carries the eggs with him, providing a sufficient amount of oxygen and protecting him from fungus. Gravediggers work together to bury a dead mouse or other small animal, raking the soil under the animal's corpse and moving it to the very end of the “cave.” There they lay their eggs, and the female (and sometimes both partners) remains to watch over the offspring, feeding the larvae parts of the dead animal. The care for offspring of termites, ants, and bees and wasps living in colonies is interesting: the offspring remains in the nest until they grow up. Working individuals do not reproduce, returning to their nest throughout their lives.

Female birch bugs guard their eggs. To protect them, they turn their backs to their enemies.

Complete and incomplete metamorphosis of insects

Incomplete metamorphosis of insects

The larvae of cockroaches and grasshoppers, barely emerging from the egg, already resemble adult insects of their species. They are only smaller in size, and their wings and reproductive organs have not yet developed. During growth, these insects do not change that much. In this case, they speak of incomplete transformation. An insect nymph emerging from an egg is very similar to an adult insect; nymphs are larvae that undergo incomplete metamorphosis. In young mayflies and dragonflies, the wings are barely visible, but with each change of shell they become more noticeable.

Complete transformation of insects

The insect develops from an egg, followed by several stages of a caterpillar, which turns into a pupa; then an adult insect hatches from it, thus passing through many stages of transformation. More than four-fifths of all insects develop through the pupal stage. This transformation is called complete. Butterfly pupae are completely different from their parents. In addition to three pairs of legs on the chest, like an adult butterfly, the pupa has five more pairs of legs, with the help of which it moves and holds tightly. The larvae of beetles, flies and bees are also completely different from adult insects. At the end of the larval stage, the insect changes significantly: it no longer accepts food, seeks shelter and enters the next stage: pupation. Butterfly pupae spin a cocoon from long silk threads produced by one of their glands. The pupa only appears motionless from the outside: inside it, significant transformations of the larval organs into the organs of an adult insect take place. The intestines, tracheal system, nervous system And pectoral muscles. The herbivorous wingless creature grows into a nectar-eating flying insect. Depending on the type of insect and conditions environment it emerges from the cocoon after a few days, weeks or months.

Reproduction of insects. Reproduction is a complex process that ensures an increase in the number of organisms. In insects, like many other plant and animal organisms, the reproductive period begins after a long period of nutrition, growth and development. During the period of feeding, growth and development, many insects die, so there is a biological need to make up for this loss. If the intensity of reproduction does not compensate for mortality, then the species becomes extinct. So in a typical case life cycle The life of an insect consists of a period of nutrition, growth and development, which is followed by a period of reproduction and settlement. Settlement - important stage in the life of adult insects, which tend to be evenly distributed over all areas and areas where they have food sources and other conditions necessary for survival.

It is important first of all to pay attention to the prerequisites that most species have for rapid reproduction. If we determine the potential fertility of the well-known housefly, taking into account the fact that in individual clutches there are about 100 eggs, and there can be up to 5 such clutches from each female over the summer, then as a result, during the season one female will theoretically give birth to offspring exceeding hundreds of billions of copies.

Among insects, there are few economically important pests that cause serious damage to agriculture and forestry.

Thus, the harmfulness of insects attacking agricultural crops, orchards, vegetable gardens, forest plantings, is closely related to their numbers. Insects cause damage periodically, when the number of a particular pest increases greatly and the period of its mass reproduction begins. The same species does not cause economically significant harm during periods of low abundance.

IN Lately Much attention is paid to issues of nature conservation, including insects. Everyone knows that a huge number of insects feed on plants, eating their leaves. Previously, many of these insects were included in the list of pests to be destroyed. Modern approaches to problems of nature conservation provide reason to reconsider this issue and include among pests only widespread species of insects that severely damage plants and thereby cause significant economic damage.

Egg. Insect reproduction ends with the female laying a large number of eggs, each of which, under favorable conditions, turns into a larva and then into an adult insect.

Some insects do not lay eggs, but small larvae that hatch from eggs in the genitals inside the female's body. This viviparity is an adaptation to reduce the mortality of offspring, since many eggs die due to unfavorable conditions or are eaten by predators. In a typical case, the female insect lays eggs, which, if they do not overwinter, take several days to develop.

Larva. The feeding, growing and developing phase of the insect's life cycle is called the larva. All insects, without exception, have larvae. The larvae emerge from the eggs extremely small. They feed continuously and voraciously and usually increase in size quickly.

However, as mentioned above, the body of insects, including larvae, is covered on the outside with a durable chitinous cover. Unlike adult insects, the body covers of larvae are softer, capable of stretching, otherwise their growth would be impossible. Nevertheless, the ability of the integument to stretch is not unlimited, and after a certain period of feeding and growth of the larva, the integument becomes an obstacle to a further increase in its size.

A crucial period begins - molting. During preparation for molting, the larvae stop feeding, become inactive, and new covers appear under their covers, much more spacious. After the larva's body has prepared for molting, the old integument bursts in the area of the head and gradually slides to the rear end of the body as a result of muscle contraction. The larva is completely freed from the old integument, its new integument hardens and becomes colored. She is back to vigorous eating and growth.

There are 3-6 such molts during the period of larval growth, but there can be significantly more. Preparation for molting is a complex physiological process regulated by special hormones.

Nutrition, as already emphasized above, is the main purpose of the larva in the life cycle of an insect. The larva accumulates reserve substances in the form of a reserve of proteins, fats and carbohydrates. Adult insects often do not feed at all and have underdeveloped mouthparts. In females of such insects, the development of eggs is carried out due to the reserves accumulated by the larva. The appearance of the larvae is extremely varied and depends on adaptation to the environment in which they live.

Complete and incomplete transformation. Doll. In the simplest case, adult insects and their larvae live in the same conditions. Well-known examples include locusts and grasshoppers living among herbaceous vegetation, or cockroaches living in plant debris, in various crevices, etc. With this lifestyle, the larvae have the same adaptations as adult insects. For this reason, a larva emerges from the egg, outwardly similar to the parents, but much smaller in size, not yet capable of reproduction and without wings.

Gradually, during the process of feeding and growth from molt to molt, the size of the larvae increases, wing rudiments appear in them, and reproductive organs develop (Fig. 10). The larva becomes more and more like an adult insect. Finally, the last molt occurs and an insect hatches from the skin of the larva, capable of flying (spreading) and reproducing.

Otherwise, the transformation of the larva into an adult occurs in cases where different phases life cycle of an insect live in different conditions, i.e. they have various devices. Thus, the larva of the May beetle or a closely related species, the beetle beetle, develops in the soil, feeding on plant roots, while the adult beetle lives openly on plants. In these cases, the larva and adult insect are completely different from each other (Fig. 11).

The larva of the cockchafer has a thick, dirty-white body, bent in a semicircle, and a large brown head equipped with sharp mandibles adapted for gnawing roots. She does not have compound eyes or any rudiments of wings; Its legs and antennae are short and bear no resemblance to the legs and antennae of an adult beetle.

With such a sharp difference between larvae and adult insects, a whole period of restructuring of external and internal organs larvae into the corresponding organs of the adult insect. Due to the need for this restructuring, the pupal phase occurs in the life cycle of insects.

The pupa is the resting phase of the life cycle. The pupa does not feed, does not grow, does not move, and is usually only able to weakly move its abdomen. The pupa is formed from the larva before the last molt, is freed from the larval skin and is characterized by a completely different structure than the larva; in the external appearance of the pupa, the signs of an adult insect are already clearly visible - legs, antennae, wing covers, etc.

The pupa is completely defenseless, so the larvae of many insects, before turning into a pupa, build special shelters in which it is protected from enemies. Thus, the caterpillars of some butterflies weave a special cocoon, many soil beetles pupate in caves with dense walls, etc.

Over the course of several weeks, complex changes occur in the body of the pupa, some organs disintegrate, others undergo partial restructuring, including the nervous system. Finally, the skin of the pupa most often bursts along the longitudinal dorsal seam and gradually the legs, antennae, and wings are pulled out of the corresponding pupal covers. Molting often lasts several hours.

The wings of the insect emerging from the pupa are soft, often wrinkled, and colorless. The insect itself also has soft covers, is not able to move quickly and is completely defenseless. The wings expand as a result of the rush of blood and then harden and become colored. In the first hours after molting, the integument on the entire body of the insect also hardens and becomes colored. After this, beetles, flies and other insects emerging from the pupa acquire the ability to fly, feed, and reproduce.

The above materials characterize two main types of insect development.

Development with complete transformation goes through 4 phases: egg, larva, pupa, adult insect (Fig. 11).

During development with incomplete transformation, there is no pupal phase in the life cycle, but there are only 3 phases: egg, larva and adult insect (Fig. 10). Hence the name of the transformation - “incomplete”.

However, these two types of transformation do not exhaust the entire diversity of insect life cycles. For example, the question of what transformation was the original one in insects requires clarification. The answer to this question is complex. This type of transformation is characteristic only of those insects that initially did not have wings, i.e., their most ancient groups - the bristletails. This primitive transformation is characterized by gradual changes appearance insect, and molting continues in insects that have begun to reproduce. This type of transformation is called primary transformation (protometaboly). Although complete (holometaboly) and incomplete (hemimetaboly) transformations, as already noted, are the main types of transformation in insects, in addition to them and primary transformation, there are other types of metamorphosis. Special type It is believed, for example, the transformation of insects of ancient aquatic groups - dragonflies and mayflies. Their larva bears little resemblance to an adult insect, but there is no pupal phase.

Based on complete transformation, as a result of its further complication, the so-called excessive transformation (hypermetamorphosis) arose in some beetles and flies. Thus, in the red-headed spanka from the family of blister beetles, the larvae different ages outwardly they differ sharply (Fig. 12). The first instar larva is very mobile, it actively searches for a clutch of locust eggs (pod) in the soil, penetrates it, molts and turns into a thick, sedentary larva, which is busy only with feeding. Thus, the differences between larvae of different ages are explained by the fact that they lead a different lifestyle.

It should be borne in mind, however, that not all insects with complete metamorphosis have larvae and adult insects currently living in sharply different conditions. Butterflies and their caterpillars, leaf beetles and their larvae live on plants, i.e. in similar conditions. Such exceptions are explained by the fact that some beetles and most butterflies switched to a similar way of life later, after the development of complete transformation had occurred in their ancestors. In this regard, it is interesting to note that the most ancient groups of beetles and butterflies have larvae that develop not on plants, but secretly, in the depths of various substrates.

The biological essence of the transformation of insects is largely similar to what is observed in other groups of animals. In the initial period of development, the insect must eat and grow quickly. This task is performed by the larvae. Adult insects often do not feed at all. They have other functions - reproduction of the species and its resettlement in new favorable habitats.

Biology of the cockchafer. The cockchafer (Table 1, 4) is included in large group harmful insects from the family of lamellar beetles, the larvae of which gnaw the roots of plants.

In the western regions of the USSR, the name "chafer" actually combines two different, but very similar in appearance: the western chafer and the eastern chafer. Only the latter species is found in Siberia.

The May beetle overwinters in the soil and comes out when the buds on the birch tree open and the first ones appear. spring leaves. During the day, beetles hide in the crowns of trees, and at dusk, after sunset, they begin to fly. They are only attracted to crowns deciduous trees(birch, maple, oak, aspen, etc.), near spruce or pine trees they appear rarely and mostly by accident. This behavior is explained by the fact that the beetles feed mainly on leaves, and very rarely on larch needles or pine inflorescences. If there are a lot of beetles, then all the young spring leaves are eaten.

The cockchafer develops in the soil. A mature female burrows into the soil to a depth of 20 - 30 cm and lays up to 70 oblong eggs there. Females choose sites for laying eggs very carefully. The beetles do not fly into the thicket of the forest, but gather on the edges and fields adjacent to the forest.

This behavior of females leads to the fact that they concentrate in certain places with favorable conditions, where their numbers are very high. They are especially attracted to pine nurseries and young plantings that are well-warmed by the sun.

The larvae develop slowly and middle lane USSR winter 3 times, i.e. the life cycle of the cockchafer is completed in 4 years. Large beetle larvae that gnaw the roots of young pine plantings are especially harmful. The eating of pine roots can be so significant that such a tree can be easily pulled out of the ground. There are known cases of the destruction of pine plantings by the larvae of the cockchafer in areas measuring thousands of hectares. Thus, the harmfulness of the cockchafer is explained by the fact that females concentrate in certain areas of the forest and field, where they lay many eggs at once. As a result, the number of cockchafer larvae during the breeding periods in these areas becomes alarming and they damage root systems forest crops, preventing forest regeneration.

Rare and endangered species(Table 3). As already noted, the vast majority of insects are of no economic importance; their vital activity is indifferent to the human economy. However, it does not follow from this that a person can be indifferent to such insects that are neutral to him. Firstly, many of these insects decorate nature and have great aesthetic significance for people who treat nature with love and care, and there are more and more such people nowadays. In addition, these billions of insects, harmless to humans, are absolutely necessary for the normal existence of huge and rich natural natural complexes. Suffice it to say that many invertebrate and vertebrate animals feed on insects, which in the absence of this food source are doomed to starvation, and many to death. Therefore, the great concern of thinking people is the depletion of natural complexes, the disappearance from them of a number of plants and animals, including insects.

In most cases, these unfavorable phenomena are associated with the industrial activities of mankind. The area of cities is growing, large areas are being developed for agricultural production, industrial complexes are emerging where minerals are discovered, etc.

A huge number of insects die when pesticides are used to protect agricultural and forest lands from any strongly multiplied pest: after all, pesticides kill not only this pest, but also other species, including beneficial ones.

Many insects that were relatively common just a few decades ago are now rare and need protection. These are mainly large beetles and butterflies, which have become rare due to the reduction in the area of natural habitats where these species lived and the reduction in food sources available to them.

The stag beetle (Table 3, 2), for example, becomes rare species due to the reduction of forest areas suitable for its life in the southern regions of the country. This beetle can only exist in old forests with an abundance of large rotting trees, in the wood of which its larvae develop.

The great oak woodcutter (Table 3, 3) was previously considered a pest of oak forests. Its larvae lived in large hundred-year-old oak trees and damaged their wood. There are almost no such oaks left now. In some countries, areas with old oak trees are protected in order to also preserve the great oak woodcutter.

The largest woodcutter of the USSR fauna is the Ussuri longhorned beetle, reaching a length of 10 cm and found on Far East, is also experiencing oppression due to the cutting down of old forests. This species, like the stag beetle, develops in the rotting wood of century-old oaks, elms and other deciduous trees.

Many large insects - butterflies, dragonflies, orthoptera, etc. - have become rare and need protection. In the USSR and many other countries, the so-called “Red Books” have been published and are being prepared for publication, which describe species of animals whose extermination is punishable by law.

There are few insects protected by law, but every amateur entomologist should understand that catching insects for one's own pleasure can harm nature. It is much more useful to direct your efforts and knowledge to the protection of insects in general, especially rare and endangered species

Thus, an insect with incomplete metamorphosis goes through three stages in its development: egg -> larva ->adult insect (Fig. 101).

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Homoptera. This group belongs to cicadas(Fig. 102, 6 ) And aphids. Their mouthparts are of the piercing-sucking type, and their wings are usually folded into a roof. Homoptera feed on plant sap. Cicadas are fairly large (up to 7 cm long) diurnal insects and are known for being able to produce very loud sounds using special organs located at the base of the abdomen. Aphids are small insects several millimeters long. Among them there are both winged and wingless forms.

Bedbugs, or Hemiptera. Insects of this order are so called because their fore wings (elytra) are dense in front and soft in back (Fig. 102, 2 ). The second pair of wings lies under the first. It is with the help of the second pair of wings that bedbugs can fly. Some, for example bed bug, wings are missing. The mouthparts of bedbugs are piercing-sucking. Among bugs there are species that feed on plant juices, there are predators and bloodsuckers (bed bugs).

Insects with complete metamorphosis

Thus, insects with complete transformation go through four stages in their development: egg -> larva ->doll -> adult insect (Fig. 103).

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Beetles, or Coleoptera(Fig. 104, B). Representatives of this order have dense, hard elytra that cover the second pair of leathery wings, with the help of which they fly. The mouthparts are gnawing. Among the beetles there are many herbivores. There are also predators that hunt other insects and carrion eaters. Beetles live in the ground-air environment (on plants, the surface of the earth, in the soil) and in water. Beetle larvae are both very mobile predators, living openly, and sedentary, worm-like, living in shelters and feeding on plants, fungi, and sometimes decomposing remains of organisms.

Incomplete transformation: egg -> larva -> adult insect (orders Dragonflies, Orthoptera, Homoptera, Bugs); complete transformation: egg -> larva ->doll -> adult insect (orders Lepidoptera, Coleoptera, Diptera, Hymenoptera).