Post-embryonic development, otherwise called post-embryonic, in all organisms that inhabit our planet, can be divided into two forms: direct and indirect. The first type is inherent in reptiles, birds, and mammals. The young born or hatched from the egg are a small copy of the adult. Another form of development is found in fish, amphibians and arthropods. In this article, using specific examples, we will consider the stages of development of insects.
The biological role of metamorphosis
The development of various animal species with incomplete and complete transformation (metamorphosis) provides the most optimal conditions for the life of juvenile and adult forms and reduces competition for food between them. This allows the use of alternative food resources, and also contributes to the dispersal of a species that occupies a different habitat (air, ground, water or underground). Insect metamorphosis is one of thereasons for the colossal number of species of these organisms currently living on Earth (more than one million). They occupy almost all existing ecological niches. Insects represent a phylum class of arthropods. The stages of insect development are the following phases: egg (embryonic development), larva, pupa, adult (postembryonic development).
The egg stage is the first and obligatory phase of the life cycle of insects. It has multiple skins. 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 riddled with pores. The second membrane, vitelline or serous, is in direct contact with the developing embryo. Its nutrition comes from the yolk. The shape, color of the chorion and the size of the eggs of various insects are varied. So, in grasshoppers, the egg length reaches 11 mm, and in spider mites - only 0.14 mm. Most insects lay eggs, although there are also viviparous forms, such as the Madagascar cockroach. The larva emerges from the egg, which is the next stage of insect development.
Full Transformation
It is typical for species of the subclass winged insects. Before becoming an adult individual - imago, the organism, having left the egg, goes through two completely different life stages: larvae and pupae. Insects that are characterized by complete metamorphosis are called holometabolic. These include orders of Lepidoptera, Diptera, Coleoptera, etc.
Features of the larval stage
They are, first of all, in the anatomical structure of the body. Most larvae lack a reproductive system. The oral apparatus is also different, and hence the type of food. Consider the larval stages of development of insects with incomplete metamorphosis.
One of the oldest organisms, the dragonfly, lays its eggs in the water of stagnant ponds. After 20 days, and in some species after 2-9 months, a pronymph (pre-larva) appears, which lives only a few seconds, then it molts, and a naiad is formed - a real dragonfly larva. It has a small size (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 tracheae for breathing, so it often rises to the surface.
Continuing to molt and grow, it crawls out of the water onto the stems of aquatic plants and transforms into an adult insect - a dragonfly with soft wings and body covers. She doesn't move for a while. The chitinous layer covering the insect hardens. The dragonfly becomes capable of flight. Summing up, let's say the following: the larval stage in dragonflies of various species ensures the expansion of the habitat of these insects. Note that a mature dragonfly insect and its larva have similarities in the way of feeding (both are predators), as well as respiration (organs - tracheas). The difference lies in their habitat: adults live in the air, and naiads live in water.
Insect larvae withcomplete transformation
In representatives of the Lepidoptera order, for example, in butterflies, they are called caterpillars and are very different from an adult. The larva comes out of the egg, gnaws through its shells and immediately begins to eat leaves and other parts of the plant with its powerful jaws - mandibles. Its body is worm-like, with a head, three thoracic and ten abdominal segments. The covers are equipped with hairs - bristles. Butterflies are insects that are characterized by complete transformation. On the lower lip of the larva is a steam gland that secretes a secret. Freezing in air, it forms a thread that the larva uses to form a cocoon. Staying in it, the larva turns into a chrysalis. She can live from a few weeks to one to three years, and the chrysalis chrysalis lives up to 10 years. Her body produces glycerin and betaine, natural antifreezes.
Butterfly larvae - insects that have a complete transformation, often molt. Their last molt ends with pupation. In some species of insects, the larvae have separate names. For example, in sawfly beetles it is a caterpillar, in pollen beetles and dark beetles it is a false wireworm, dragonfly larvae are called naiads, and their prelarvae are called nymphs.
What is a chrysalis
This is the phase of the life cycle of insects, which leads to the development of a sexually mature individual - 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 particles of sand or shells to build a cocoon and strengthen it. Free pupae have antennae, legs andthe wings of the future individual imago are free and pressed to the body. Covered pupae are characteristic of many species of butterflies, ladybugs, and some Diptera.
Imago
For the last stage of development of insects, the formation of the reproductive (reproductive system), as well as all the external signs inherent in this species, is characteristic. Like the larva, the adult performs the function of dispersal of insects in different habitats. In addition, adults are responsible for reproduction and have sex organs. In males, they are called testes, and in females, they are called ovaries. There are also adnexal glands that secrete secretions and copulatory organs for mating.
In this article, we examined the stages of development of insects that have indirect development with incomplete and complete transformation.
