Postembryonic development, otherwise calledpost-embryonic, in all organisms-inhabitants of our planet, can be divided into two forms: direct and indirect. The first species is inherent in reptiles, birds, mammals. Born or out of an egg cub are a small copy of an adult. Another form of development is found in fish, amphibians, and arthropods. In this article, we will look at the developmental stages of insects with concrete examples.
The biological role of metamorphosis
The development of various species of animals with incomplete andcomplete transformation (metamorphosis) provides the most optimal conditions for the life of juvenile and adult forms and reduces competition for the food supply between them. This allows the use of alternative food resources, and also contributes to the resettlement of the species occupying different habitats (air, land, water or underground). Metamorphosis of insects is one of the reasons for the colossal number of species of these organisms that now live on Earth (more than one million). They occupy almost all existing ecological niches. Insects represent a class of arthropod type. The stages of insect development are the following phases: egg (embryonic development), larva, pupa, imago (postembryonic development).
The egg stage is the first andmandatory phase of the life cycle of insects. It has several shells. The first is called the chorion (performs a protective and mechanical function). In some species, it is complicated by layers of wax or chitin and penetrated by pores. The second membrane, yolk or serous, is in direct contact with the developing embryo. It is powered by the yolk. The shape, color of the chorion and egg sizes of various insects are diverse. Thus, in grasshoppers, the length of the egg reaches 11 mm, and in spider mites, it is only 0.14 mm. Most insects lay eggs, although there are also viviparous forms, for example, Madagascar cockroach. From the eggs comes the larva, which is the next stage of insect development.
Complete transformation
It is characteristic of species of the winged subclassinsects. Before becoming an adult individual - an imago, the organism, having emerged from an egg, experiences two completely different life stages: larvae and pupae. Insects characterized by complete metamorphosis are called holometabolic. These include orders of Lepidoptera, Diptera, Coleoptera, etc.
Features of the larval stage
They consist primarily in the anatomicalbody structure. Most larvae lack a reproductive system. Also differs oral apparatus, and hence the type of food. Consider the larval stages of insect development with incomplete transformation.
One of the most ancient organisms is a dragonfly,lays eggs in the water of standing water. After 20 days, and in some species, 2–9 months, the prononym appears (predlichinka), which lives only a few seconds, then it molts, and the naiad is formed - a real dragonfly larva. It has small dimensions (1.5 mm), and the life cycle, depending on the type of insect, can last from several days to one to three years. The larva actively hunts in the water and has tracheas for breathing, therefore it often rises to the surface.
Continuing to fade and grow, it crawls out of the water.on the stems of aquatic plants and transformed into an adult insect - dragonfly, having soft wings and body integument. For a while she does not move. The chitinous layer covering the insect hardens. The dragonfly becomes capable of flying. Summing up, let's say the following: the larva stage in dragonflies of various species provides for the expansion of the habitat of these insects. Note that the mature insect dragonfly and its larva have similar features in the way of feeding (both are predators), as well as respiration (organs are trachea). The difference lies in their habitat: adults live in the air, and mollusks live in water.
Insect larvae with complete transformation
Representatives of the Lepidoptera order, for example,butterflies, they are called caterpillars and are very different from the adult. The larva comes out of the egg, gnawing at its shell and immediately begins to eat the leaves and other parts of the plant with its powerful jaws - the mandibles. Her body is worm-shaped, has a head, three thoracic and ten abdominal segments. The covers are provided with bristle hairs. Butterflies are insects that are characterized by complete transformation. On the lower lip of the larva is a steam gland that secretes a secret. While frozen in the air, it forms a thread that the larva uses to form a cocoon. Staying in it, the larva turns into a pupa. She can live from a few weeks to one to three years, and the baby doll of a wolf lives up to 10 years. In her body, glycerin and betaine are formed - natural antifreezes.
Butterfly larvae - insects having fulltransformation, often molt. The last molt ends in pupation. In some insect species, the larvae have separate names. For example, in the sawfly beetles, this is a caterpillar, in pollen specimens and dark-browed beetles, it is a foxwire, naiads call dragonfly larvae, and their prelarvae are called nymphs.
What is a doll
This is the phase of the life cycle of insects, whichleads to the development of sexually mature individuals - imago. The pupal stage is characterized by the fact that the organism does not feed and cannot move. In addition to silk, animals often use sand or shell particles to build a cocoon and strengthen it. In free pupae, the antennae, legs, and wings of the future imago are free and pressed to the body. Covered pupae are characteristic of many species of butterflies, ladybirds, some dipterans.
Imago
For the last stage of insect developmentcharacteristic is the formation of the reproductive (reproductive system), as well as all external features inherent in this species. Like the larva, the imago performs the function of settling insects in different habitats. In addition, adults are responsible for reproduction and have sexual organs. In males, they are called testes, and in females, they are called ovaries. There are also accessory glands secreting a secret and copulatory organs for mating.
In this article, we examined the stages of development of insects with indirect development with incomplete and complete transformation.
