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Imago - what is it? The adult (definitive) stage of individual development of insects and some arthropod animals

Insects throughout their lives experience a profound restructuring of the external and internal structure of the body. In other words, the metamorphosis inherent in all animals. But it only takes place in them with characteristic and very specific features. Postembryonic development of an insect is, as a rule, three consecutive stages: an egg, a larva, an imago. In many species there is an additional stage: the triungulin, pupa, etc.

Depending on how many stages of development the insect passes, it can be attributed to one of two large groups: with incomplete or complete transformation. Thus, the method of metamorphosis should be regarded as one of the main criteria of classification.

From the article you will learn important features of the stages of development of insects with complete and incomplete transformation, with hypermetamorphosis.

Imago - what is it?

The word "imago" is of Latin origin and is literally translated as "image". In zoology, this term refers to the adult (final) stage of development of animals with a complex life cycle (insects and some arthropods). The phase is final. With its onset, the animal acquires the ability to reproduce and, as a rule, to resettlement. The adults are not prone to molting. At this stage, the growth of insects and arthropods ceases.

Depending on what kind of metamorphosis is typical for each individual species, the stage of imagoes can start in different ways.

Development with incomplete transformation

For incomplete transformation is characterized by three stages of development of insects: an egg, a larva and an adult. A characteristic feature of this type of metamorphosis is the similarity of the appearance of the larva from the imagos, like the latter, they have oral organs, complex eyes, expressed rudimentary wings. Moreover, there is often a similar way of life. Larvae of insects with incomplete transformation are called nymphs.

This type of metamorphosis is observed in the Spiny-winged, Cockroach, and Anaerophanes.

Development with complete transformation

With complete transformation, insects and arthropods pass from 4 to 5 stages of development: the egg, the larva, the pupa and the adult. Sometimes you can determine the stage of pre-pups. The larva in this case for adult shoes is almost not similar to understand this, it is enough to remember the butterfly caterpillar. It lacks the eye of the complex structure and outer rudiments of the wings and, as a rule, has a different type of mouthpiece.

After the true larva finishes its growth, it stops eating, becomes immobile and turns into a pupa. Then the adult hatch from it. True larvae are divided into three groups: caterpillar, worm-like (beetles, Diptera, etc.), camp-like (ground beetles, water-beetles, etc.).

This kind of metamorphosis is typical for all Lepidopteran (butterfly), Horsecloth, Diptera.

Development with hypermetamorphosis

The most difficult way to develop insects is hypermetamorphosis. It is characteristic of some beetles (micromaltus, bloopers, etc.), retina, flies-buzzing, a number of hymenoptera.

With hypermetamorphosis, the larval stage of development of insects passes in several stages. There are strong differences in the structure and lifestyle of larvae of different ages. At the first stage they do not eat, but at the same time they actively move and settle. The older larva, as a rule, lives in a specific habitat. It not only eats, but also grows. Sometimes, in order to move from one active form to another, the organism must be restructured. In these cases, the larva becomes immobile and stops feeding. The so-called "spoon-doll" is formed. In the future, as, for example, in beetles from the family of napers, it turns into a real pupa, from which the imago beetle develops.

Features of the structure of adults

As already mentioned above, the final stage of development of insects and some arthropods is the imago. What it is is easy to understand, referring to the original language. In some sources, the term is translated as "true appearance" and it really is. Throughout their life in this stage, adults do not change much, they stop the development process. Moult is absent in most species. However, all rules have exceptions. Thus, the lower orders (bristle tails, springtails, etc.), even in the adult stage, periodically discard the cuticle.

The main differences between adult insects and young individuals are as follows. They develop wings and genitals, tendrils consist of a constant number of segments, a certain type of oral apparatus (often different from that of larvae) is formed. The imago is maximally adapted to the environment, and this is expressed in adaptive mechanisms and many features of the structure: the features of the respiratory system, the shape of the body, the development of sensory organs, additional protective mechanisms,

For the vast majority of arthropod animals, insects, this phase is the peak of development. Exceptions are only a few mites. They all happen exactly the opposite. Parasitic species moving inside the body cavities and host tissue lose the morphological features inherent in the adult. This process is called desimigination.

Age change in color

Hatching from the pupa and thus passing the last molt in the stage of the larva, the insect leaves its shell. Often the original color is light in tone (not white, but more pale). During a certain period (from several hours to 2-3 weeks) pigmented substances accumulate and oxidize, contacting with atmospheric air, resulting in darkening the cuticle.

Some species, for example, imago butterflies (squad Lepidoptera) appears with "its" formed color.

Change in color can be associated with certain changes in the body. Thus, the desert locust is originally yellow-green in color. During the reproduction period, accumulation of sexual enzymes takes place in the body and as a result, the integument acquires a pink shade (in the photo above).

Lifespan of the adult

The duration of the definitive stage of development can vary greatly depending on the species. The shortest is the life of butterflies from the family of Mesochnitsa, limited to just a few minutes. Species, the stage of imago in which lasts no more than 2-3 days (including podenki, chironomids), do not feed and have reduced oral organs.

Long-livers can be called social insects, such as ants and termites. Their queens and queens live up to 20 and 50 years respectively. The type of cicada Magicicada septendecim is characterized by a 17-year life cycle, which is also quite a lot by the standards of insects.

There are also very paradoxical cases in nature. For example, the familiar beetle deer (pictured above) in the adult stage spends only a few weeks, and then dies, while his larva lives up to five years.

Quite often the habitat and the larva and imago occupied by one species of ecological niche differ. For example, mosquitoes. The larva has a typical diet for a predator (plankton, bacteria) and lives in water. Imago - flying insects. Females feed on the blood of vertebrates, and males feed on juice and plant extracts.

Primary function of the adult stage

So, the final stage of the life of insects is the stage of the imago, what is it, you already learned above. Having understood the essence of the definition, having learned the main features of the structure, it is not difficult to guess what is the main function of this phase. In the adult state, absolutely all organisms reproduce and maintain the abundance of the species. If among the insects the number of oviparous females exceeds the number of males, then they are prolific. For example, the queen bee is able to postpone up to 1500 eggs per season.

The stage of the imago is important in terms of species distribution. This process is facilitated by the presence in adults of individuals of developed wings and extremities.

Affecting the general biological significance of the imaginal stage, it should be pointed out that the imago is such a peculiar manifestation of the evolutionary processes associated with the development of land by arthropod animals and their subsequent strengthening in occupied ecological niches.

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