The insects form a class Invertébré S of the junction of the Arthropode S. the insects represent 80  % of the species Animal be.

This class is subdivided in two subclasses:

  • the aptérygote S which are characterized by the absence of wing S;
  • the ptérygote S.

Their body is composed of three parts: head, thorax, abdomen and are characterized by the presence of three pairs of legs, two pairs of wings (at the ptérygotes only) and a pair of antennas (six legs, four wings and two antennas). One will notice thus that the spiders are not insects, but Arachnida.

This morphological description is a general information, the evolution having made that by specialization, certain elements can be atrophied.

Some orders of Insects

Odonate (Dragonflies)

The first formula of winged insect probably was of the dragonfly type.

The dragonflies exist on ground since 285 million years, and could reach a scale of 70 cm at the time of the dinosaurs. The current species largest reaches 19 cm of scale.

Éphéméroptère (Transitory S)

Insects close to the dragonflies, with the semi-watery life. The adults (known as in France “flies of May” are known to have one very short lifespan (not exceeding a few hours) and do not nourish themselves. The larvae live under water and are vegetarians, their development is much longer (a few years).

Dictyoptère (Cockroach S, mantes, termites)

These insects are cousins. The Dictyoptère term is old, from now on, one classifies the cockroaches in Blattoptères, Mantes in Mantoptères and the Termites in Isoptera.

The cockroach, also called cockroach or cockroach ( coquerelle with the Quebec), is a insect whose some species live in commensaux with the man, mainly in the kitchens where it nourishes remainders, waste and provisions. The few 4000 S distributed around planet vary in form, color and size. They appeared on the Earth, approximately 400 million years ago.

The termite S are social insects. They flee the light, and are often blind. Also called white ants , they is very frequent in the hot countries, where certain S build large wasted ground nests, the Termitière S, which are characteristic of the tropical plates. The termites have a great social cohesion, with the image of the ants. They show large a collective Intelligence. In Europe, the termites can cause large damage in the dwellings by digging their galleries in the sawlog, they nourish themselves some (see devastating Insecte).

The mantes result predatory from this family.

Dermaptère (Forficule)

This order gathers the common forficules, insects in the humus and the low vegetation, usually called Perce-oreille S because of their two grips at the end of their abdomen, which have utility only at the time of the bridal parades of these insects (it is not a question of weapons contrary to a widespread opinion). The female takes care of the egg S and the young larvae. Their food mode is omnivorous, in the larvae like the adults.

Embioptère (Embie S)

Small group of insects (approx. 150 species), little known, related with the forficules. Live in the tropical and moderate climates hot, do not leave the humus and shelter in tunnels made with the silk which they weave, in small colonies (made up of adults and larvae). Wings non-existent in the females, little developed in the males. Remains are nourished.

Orthoptère (Grasshopper, cricket)

There exists more than 2.000 species of crickets in the world, and one finds traces Fossile S attesting of their presence going back to the higher Trias.

This order includes the Criquet S, the Sauterelle S, cricket S and the courtillières. They move while jumping using their long posterior legs. However, certain grasshoppers have the so developed abdomen which they are not any more able to carry out truths jumps and the courtillières do not even have jumping legs.

Many insects of this kind produce a sound: they stridulent by producing their song by friction their legs posterior on a vein of the élytres in the locusts, or by rubbing their wings one against the other in the grasshoppers. This song of summer brings them closer to the cicada S, which are hémiptères, therefore pertaining to an order completely different from Orthoptères. Certain coleopters are also in measurement of striduler with their wings…

Orthoptères are characterized by posterior wings, with symmetrical folds (ortho-: right and - ptère: wing, in Greek), which is unfolded with right angle with the remainder of the body and is folded up like a range under the " tegmina" (corresponding to the élytre S at the coleopter S).

Hémiptère S (bug S, cicada S,…)

The characteristics of the hémiptères (Hemiptera) are:

  • of the long antennas,
  • of the piqueuses oral parts with a length rostre,
  • two pairs of wings of which one, partly cornea, are transformed into hémiélytre.

Coleopters (Cockchafer, ladybird,…)

The coleopters (coléo-: protection in Greek) are characterized by:
  • of the former, élytre S, thick wings and corneas, generally covering the totality of the abdomen.
  • of the posterior wings (if they exist), membranous and folded up at rest under the élytres.
  • of the crushing oral parts.
The order of the coleopters is the order of the animals which gathers the greatest number of species.

Hyménoptère (bee, Wasp, ant)

The hyménoptères constitute, after the coleopter S, the order of insects more diversified. One currently evaluates their number with more than 120.000 species. This order includes/understands the bee S, the ant S, the Guêpe S.

Their name comes from the wings Membrane use that the majority of the insects hyménoptères carry per pairs. The word comes from the Greek hymên , “marriage”, and ptéron , “wing”. That comes owing to the fact that there exist hooks on the former vein of the posterior wing making it possible this one to be coupled with the former wings.

The characteristic more striking hyménoptères is that many species are social insects (like also the Termite S).

Dipterous (Fly S, Mosquito S)

The dipterous are characterized by the possession of only one pair of wing S (di-: two in Greek). Besides the etymology indicates the unicity of the pair of wings (di two; ptères wings). However, certain species are apterous the such Hippobosque S which live their adult stage on the animal that they parasitize. The other pair of wings was transformed into “haltères”, which are tiny small bludgeons being used as beams for the stability of the vol.

This order essentially contains the Mouche S, the Moucheron S, the mosquito S and the " cousins".

In spite of the unpleasant or dangerous character for the human health of certain species, the majority play an important ecological part. Not only they take part to a large extent in the elimination of the excrements (species Coprophage S) and corpses (species Nécrophage S), but their larvae which often live in the ground produce significant amounts of humus.

Lépidoptère (butterfly S)

The oldest fossil is Archaeolepis basket Jurassic English, gone back to approximately 190 million years.

The lépidoptères are characterized by two pairs of wings covered with scales (from where name lépidoptère ). In a state of larva, the lépidoptères manufacture Soie, and then often form a Cocon.

The development of the caterpillars is generally carried out in five stages marked by moults until the transformation into chrysalis. According to the species, the nymphose takes place with the free air and the caterpillar is surrounded sometimes of a silk wire cocoon before being transformed into chrysalis or it takes place under ground.

Siphonaptère (chips)

All the species of this kind are adapted to a specific lifestyle. The ectoparasitic adults live in the hairs and the feathers of the mammals and the birds, and nourish themselves of their blood. They lost completely the use of the flight but are able to jump very high, up to 300 times their own height thanks to their powerful posterior legs. All the species are of very small size (a few millimetres length).

The larvae, which live in the grounds (including inside the dwellings), are vermiform and détritivores.

Anatomy and Physiology

The insects are covered with a Cuticule Chitine uses as all the Arthropode S. It acts of a Exosquelette which enables them to limit the water losses in air medium.

The Respiration of the insect is made thanks to invaginations of the tegument called Trachée S which constitute a network bringing the Oxygène directly to the cells. These tracheas open on outside by respiratory mark S with variable opening, on the sides of the segments (pleurites) thoracic and abdominal. The circulatory apparatus thus does not have or little role for the Respiration (with some exceptions near as the larvae of chironomist - dipterous alive in mediums very slightly oxygenated - which have Hémoglobine).

The interior medium consists of Hémolymphe which is put moving by dorsal contractile vessels and the general muscular movements of the insect. The circulatory apparatus is opened, with low pressure.

the digestive system consists of an intestine in three parts: stomodeum (internal former), mesenteron (internal means) and proctodeum (internal posterior). Stomodeum and proctodeum are covered with cuticule since they result from invaginations of the tegument.

The food Régime of the insects is very variable: herbivore (caterpillar S, Locust), Coprophage (dung-beetle), Predatory S (Dragonfly S), necrophagous, nectarivore (butterflies), nozzles of saps (Plant louse S) or of blood (mosquito S females). Certain insects (xylophagous) can nourish themselves of wood (termite S). Certain insects can change food mode during their life (mangeuses caterpillars of sheets and adult butterflies nectarivores). The oral appendices are very variable in the insects and related to their food (appendices of the crushing type (Criquet), nozzle with horn dévaginable by surge of hemolymph (adult butterfly), stitcher-nozzle (mosquito), bootlicker-nozzle (bee)…)

the central Nervous system consists of a ventral ganglionic chain. To before the ganglia migrate dorsalement and amalgamate to form a brain. The ventral following ganglia amalgamate to form a ganglion under-œsophagien which innerve oral parts.

Development

The majority of the insects develop egg at the adult stage called Imago while passing by several metamorphosis S: larval stage (caterpillar, Worm S,…) and stage nymphale (Chrysalis, Pupe,…).

The development is controlled by a hormone steroid, the Ecdysone, which is produced in prothoracic glands and induces the driven . Another hormone, the youthful Hormone, a derivative Terpénoïde, inhibits the metamorphosis. It is produced in the Corps allate S, of the endocrine bodies close to the esophagus. One distinguishes the primitive insects, without metamorphosis ( Amétabole S ) of those which undergo a metamorphosis, among which one finds:

  • the Hétérométabole S (including/understanding the Hémimétabole S and the Paurometabolous S), at which the larval and adult stages have often comparable lifestyles, with a progressive growth of the wings.
  • the Holométabole S (insects with metamorphosis supplements) at which larval and adult stages are very different (caterpillar and butterfly for example) and separated by a stage called nymph during which the wings are formed.

The reproduction of the insects is also controlled by the ecdysone and the youthful hormone , which act in the two sexes. These hormones control the operation of the reproductive apparatus, but do not influence the determination of the sexual characters, which are strictly given in a genetic way. The hormones of the type Phéromone S play also an important role for the attraction and the recognition of the individuals within a species.

Insects in the world

Ecology

The insects are pledged with the emerged grounds. Some live in Fresh water and of rare exceptions in Mer. One finds them under almost all the climates, of hottest with coldest.

Biodiversity

Classification

Place des insects in the animals

According to Kjer , which analyzed the sequencings of ribosomal ARN 18S, the Insects is closer to Molluscs than of Myriapodes . Consequently, they would be in fact Molluscs which adapted to the dry land and which colonized it.

Orders

Orders: Phasmoptère S Chéleutoptère S
  • Plécoptères
  • Protorthoptère S - extinct -
  • Psocoptères
  • Raphidioptères (Raphidie)
  • Strepsiptères (Parasitic of the insects)
  • Thysanoptères
  • Trichoptères
  • Zoraptères

According to ITIS

Classification

The classification of the insects was proposed by Carl von Linné at the 18th century on the basis of morphological criterion. With the appearance of the genetics, Pussy and Bourgoin proposed a phylogenetic news Classification which is not entirely adopted and is the subject of a continuous revision (all the genetic analyzes were not made yet, for more information on classification lira the article on the Systématique). Classification below tries to take account of this new classification.
  • Hexapodes
    • Insects
      • Archéognathes
      • CNN (clade not named)
        • Thysanoures
        • CNN
          • Odonates
          • CNN
            • éphéméroptères
            • Néoptères
              • CNN
                • CNN (nondetailed)
                  • Blattoptère S
                  • Mantoptère S
                  • Isoptère S
                  • Plécoptéroïde S
                  • Orthoptères
                  • Dermaptère S
                  • Grylloblatoptère S
                  • Embioptère S
                  • Phasmatodea
                • CNN (nondetailed)
                  • Zoraptère S
                  • Psocoptère S
                  • Phthiraptère S
                  • Hémiptère S
                  • Thysanoptère S
              • CNN
                • CNN (nondetailed)
                  • Strepsiptère S
                  • Coleopter S
                  • Névroptère S
                  • Raphidioptère S
                  • Mégaloptère S
              • CNN (nondetailed)
                  • Hyménoptère S
                  • Mécoptère S
                  • Siphonaptères
                  • Dipterous S
                  • Trichoptère S
                  • Lépidoptère S

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