Baby doll

According to morphological features, the Metabola pupa corresponds to the nymph (larva) of the last age in other insects: it has a more or less similar structure to the imaginal structure of the body, eyes, antennas, legs, and the most developed protoptera (predecessors of the wings). At the same time, it differs sharply from the larva, in which at least the structure of the eyes, antennae, and legs is fundamentally different from the pupal-imaginal one, and the protoptera are absent. The pupal stage always consists of the same age, which is the penultimate age in the insect ontogenesis: with the penultimate molt, the insect moves from the larva stage to the pupa stage, and at the last molt - from the pupa stage to the imago stage. In this regard, the Metabola pupa differs from the resting nymphs of thrips and coccid, which are 2 or 3 years old. A pupa is always unable to feed; its mandibles may be mobile or immobile (see below), other oral appendages (maxillae and lower lip) are fixed. Antennas are always fixed up to molting on imago; the antenna structure is similar to the imaginal one and differs sharply from the larval one. The legs are still bent at the knees so that the shin is pressed against the thigh; legs unable to unbend and function, at least to the state of pharathic imago; in the condition of the pharate imago, the legs either remain motionless until molting on the imago, or acquire the ability to bend their knees and move (see below). Protopteron always directed vertices ventral back and protrude ventral body. There is the following difference in the position of the appendages of the mesothorax and metathorax, not related to their imaginal or larval specializations: on the mesothorax the legs are directed forward with knees, and the protopterons are deflected backward, bypassing the base of the legs from behind; on the metathorax, the knees of the legs are deflected backward, and the protopterons are deflected forward, so that they either bypass the bases of the legs in front or lean on them. As a result, on each side of the body, the top of the anterior protopteron leans widely on the top of the posterior protopteron, and the knees of the front and hind legs protrude in front of the protopteron. Usually, the front and middle legs of the pupa are located in the same way: their hips are directed almost forward parallel to each other, and the legs and legs are directed backward, unlike the hind legs, whose hips are directed at an angle to the hips of the front and middle legs. According to the position of the protopteron and the legs, the Metabola pupa differs from the resting thrips nymphs and coccid.

Some of the pupae have a slightly changed posture In the pupae of most beetles (Coleoptera), which, like the imago, have an extended torso, the knees of the front and middle legs are not directed forward, but to the sides, while their hips remain parallel to each other and not parallel to the hips of the hind legs; in some beetles (in particular, in passalides), the front legs have lost this position and turned the legs forward. In some wingless insects (in particular, in fleas and in working individuals of ants ), due to the loss of protopterons, the hind legs of the pupa acquired a position parallel to the front and middle legs.

In the past, some authors believed that when turning a larva into a pupa, it could be covered on the outside with some kind of special membrane that spreads the limbs and makes the pupa stationary; in connection with this, a special type of pupae, “covered,” was isolated. In fact, every insect pupa, like any other arthropod at any stage of development, is covered only by the cuticle produced by the epithelial epithelium cells (hypodermis), so that the cuticle covers its entire body and its every appendage from all sides. A new cover cannot form outside the already existing insect cuticle; A new cuticle is formed only in the process of molting ; it always forms directly on top of the hypodermis cells, that is, inside of the old cuticle, and is only outside when the old cuticle is dropped. So the pupa of the pupa is formed under the cuticle of the larva. In some insects (butterflies, mosquitoes, etc.), after dropping the larval cuticle and smoothing pupal appendages (legs, protopterons, antennas, proboscis), the pupae of the pupa stick to the body, which creates the illusion that they are covered with something (see below, glued pupae).

In some sources there is a statement that in the pupa all living tissues dissolve and then re-emerge. In fact, this can not be, because in a living organism all cells are formed only from cells. According to another version, some undifferentiated tissue rudiments - “imaginal discs” are preserved in the pupa, from which the whole organism is supposedly re-formed, that is, something like the second embryogenesis occurs. In fact, in insects with complete transformation, differentiation of tissues and organs in ontogenesis proceeds in the same way as in other arthropods: at the early stage of embryogenesis (in insects - in the egg), the ectoderm, endoderm and mesoderm differentiate, the whole body is divided into segments, and in certain segments laid on a pair of limbs; in the process of further development, all these parts of the body are preserved, but can change shape and size; changes in the external structure, occurring in postembryonic development, appear only when molting. Initially, imaginal discs (Imaginalscheiben.) Identified special formations that are present in the third (last) age of the larvae of flies (Weismann 1864 ^[1] ). These formations are in an unusual way modified pre-pleats of the hypodermis that occur before the larvae moult on the pupa; only circular flies ( Cyclorapha Brauer 1863, or Discota Weismann 1866) have them, but are absent from any other insects. Later, some authors (Pratt 1899 ^[2] and others) began to call “imaginal discs” any tissue that is not subjected to lysis; in this sense, “imaginal discs” are found in all multicellular animals. As with any other moulting of arthropods, when shedding from larva to pupa in insects with complete transformation, all tissues, segments of the trunk and limbs of the pupa are formed only from the corresponding parts of the larva. In some insects with complete transformation (in particular, in round-leaf flies), when molting the larvae to the pupa, a particularly large-scale dissolution does occur and the subsequent growth of many parts of the body; However, this is not a feature of insects with complete transformation in general, since in other representatives of this taxon (in particular, in vislokrylok, camel, mosquitoes, etc.), no more tissues undergo dissolution than in some other molting of arthropods. A feature of the larval-pupal molt of all insects with complete transformation is not the scale of lysis, but special methods of transforming the legs and antennas (see below) ^[3] .

It has been suggested that the resting stage of the pupa is needed by the insect for wintering or for some other purpose related to the peculiarities of their way of life. However, this is not the case, since the presence or absence of the pupal stage is uniquely determined by the systematic position of the insect, and therefore cannot depend on its lifestyle or habitat. It is now generally accepted that the Metabola taxon, characterized by the presence of a pupa, is holophyletic, that is, descended from a single ancestor and includes all the descendants of this ancestor. This means that in the course of evolution, a complete transformation with the pupal stage arose once in one ancient species (presumably existing in the Carboniferous period ), and then was inherited by all its descendants, regardless of whether they need it or not. Despite the presence of the pupal stage at rest, most insects that have adapted to waiting for winter in the resting diapause state do not diapause at the pupal stage, but at one of the other stages (larvae, imago or egg).

In the literature, one can find the statement that, in addition to Metabola, the pupal stage is present in some other insects, namely thrips (Thysanoptera) and the male coccid (Gallinsecta). In fact, these insects, regardless of Metabola, had resting stages of development, which have some external features of the Metabola pupa, but are not identical to it. Recently, fundamental differences between coccid metamorphosis and complete transformation have been revealed ^[4] .

Pupae are toothed ( pupa dectica ) and not edentulous ( pupa adectica ). Toothy pupae have moving active mandibles , with which the pupa leaves its shelter before molting on the imago . Such toothy pupae are characteristic of , scorpions , caddisflies and the most primitive butterflies .

In most other insects, pupae are not edentulous, that is, their mandibles, like all other parts of the oral apparatus, are unable to function. All toothy pupae are non-glued.

A non-toothy pupa can be unglued and glued together ( pupa conglutinata ).

In the glued pupa, all appendages of the head and chest (antennas, oral appendages, legs, and protopters are from Greek.πτερόν "wing") glued to the body and to each other; their sticking occurs during the molt of the larva on the pupa immediately after dropping the larval cuticle. In the past, it was believed that such a pupa was covered with something on top of the cuticle , therefore, it was called “pupa-covered pupa” ( pupa obtecta ). The glued pupae are found in the majority of Lepidoptera (belonging to the Neolepidoptera taxon), in the Diptera (except for circular seals ), as well as in some coleopterans and some Hymenoptera. The glued pupae of daytime butterflies can have a golden sheen, in connection with which they are called a special term - chrysalis ( Latin chrysalis , from the Greek. Χρυσός - gold).

Movement

The pupae are unable to unbend their knees and therefore cannot move on their feet. This state continues until a new, imaginal cuticle forms under the pupal cuticle, and the imaginal muscles develop. The state of the pupa just before molting on the imago, when there is already an imaginal cuticle under the pupal cuticle, and below it the imaginal musculature, is called the pharate imago .

The movements of the pupa itself. In the overwhelming majority of Metabola, before the onset of the condition of the farath imago, the pupa is completely unable to move its legs; this applies equally to non-glued pupae (whose legs are free) and glued pupae (whose legs are glued to the body). Many pupae retain the ability to move the trunk. The pupae of some diptera (Diptera) use the mobility of the body to move. For example, kulikomorf pupae (bloodsucking mosquitoes, bells, etc.) are adapted for active swimming with abdominal movements, due to which they can escape from predators. The pupae of some dipterans, living under the dead bark of dead trees, are able to move in search of a place with suitable humidity. In most Metabola, the pupa is not capable of active movement. The pupae of some insects have generally lost their mobility. The exception is the pupa of the vislokrylok (Meganeuroptera), in which the legs can maintain mobility in the articulation with the body; in this case, like in all other pupae, the knees are always bent and cannot bend, but in danger the pupa can move a little, moving its bent legs. Some toothy pupae (pupa dectica - see above) are capable of moving the mandibles even before the onset of the state of the pharath imago.

Movement of pharath imago. In some insects pharathic imago acquires the ability to move; it leaves the shelter or cocoon in which the pupa led a still life, and moves in search of a place convenient for molting on the imago. In gold-eyed, camel and some other insects the pharate imago acquires the ability to unbend legs and actively walk on them. At caddisflies (Trichoptera) (pupae of which are under water in closed doll houses) the pharate imago, after the house has been gnawed by the mandibles and comes out of it, swims in the water with the help of strong synchronous rowing movements of elongated middle legs, and then is selected on land using the middle and front legs.

Pupation is called a molt, in which the larva turns into a pupa. This is the last molt in the development cycle of the insect; at the last molt, the pupa turns into an adult insect (imago). Before the molt on the pupa, the larva enters the state of the prepupae , or pronymph . Since the pronymph is covered outside by the not yet discarded larval cuticle, it retains the appearance of the larva, but under this larval cuticle the pupal structure is formed. As before any molt of arthropods, the hypodermis exfoliate from the old (in this case, the larval) cuticle and change its shape, acquiring the features of a new stage (in this case, the pupa).

A peculiarity of the molt from larva to pupa is that the legs change their structure in a paradoxical way: despite the fact that the larval leg is much smaller than the pupal one, after the hypodermis are detached from the larval cuticle, the hypoderm does not grow, but at first decreases strongly; leg muscles are lost; only after this decrease, the hypodermis of the leg begins to grow, and growth begins with the formation of a knee bend. As a result, the growing pupal leg is located not in the larval leg, but mainly in the trunk area of ​​the larva, only slightly reaching its proximal part of the larval leg with its tip (see Figures Chrysoperla carnea and Rhyacophyla nubila ). To date, these processes have been studied for several species from different orders; it has been shown that methods for reducing leg tissue are very diverse - from uniform anti-growth to discarding the distal part ^{[3] [5]} .

Only in Lepidoptera, the hypodermis of the leg does not decrease, but immediately begins to grow, with the result that the tissue of the pupal leg completely fills the larval leg (see photo Vanessa io ).

When the larval leg is transformed into a pupal of some insects, each segment of the pupal leg (coxa, swivel, thigh, shin, foot, pretarsus) develops the corresponding segment of the larval leg, that is, the ontogenetic homology of the leg segments is maintained; In some insects, the ontogenetic homology of the segments is broken, for example, the pupal foot may develop from the larval femur (see figure Chrysoperla carnea ) and the like; in all cases, each leg of the pupa always develops only from the corresponding leg of the larva, that is, the ontogenetic homology of the extremities is always observed.

Due to the degeneration of the leg muscles, the pronymph is unable to move with the help of the legs; in cases where the larva uses its legs for movement, the pronymph is unable to move. Therefore, in many insects, the larva builds a cocoon, cradle or other protective structure, which provides it with relative safety, before falling into the state of pronymph (see below). After molting the larvae on the pupa, the appendages of the pupa, which were previously pressed under the larval cuticle, are flattened, but the legs remain motionlessly bent at the knees. At this time, the legs are still devoid of muscle, so the pupa continues to be unable to move on its feet and remains in the same protective structure that was made by the larva before falling into the state of pronymph. In the process of molting the larvae on the pupa, the leg muscles disappear completely in all Metabola except the vislokrylok (Meganeuroptera, or Megaloptera s.str.), In which a part of the muscles at the base of the leg is retained ^[3] . Unlike other Metabola, Pronymphs and Pupae, the Little Boy is capable of moving on his feet when in danger. Despite this, they spend all their time, lying motionless in a crib, like pronymphs and pupae of other Metabola. This suggests that the mobility of the legs of the pronymph and pupae of the sprat is secondary.

When molting from the larva to the pupa, in addition to the special processes occurring in the legs, there are certain changes in the antennae and eyes.

In all Metabola, the pupa antenna develops from the entire larva antenna, so that the terminal sensilla of the larval antenna appear on top of the pupal, and then imaginal antenna; but when shedding from the larva to the pupa, the whole dismemberment of the larval antenna disappears, and then the antenna dismemberment reappears, peculiar to the pupa and imago, so that no segment of the pupal-imaginal antenna corresponds to any particular segment of the larval antenna (that is, the pupal and imaginal antenna ontogenetically homologous to the larval antenna as a whole, but in some antenna segments there is no such ontogenetic homology).

When the larvae turn into a pupa and further into imago, the larval eyes, each of which usually consists of 7 or fewer ommatidia, are completely replaced by faceted imaginal eyes (so that there is no ontogenetic homology between the larval and imaginal eyes).

In insects with wings, protopterons appear during molting from the larvae to the pupa (outer lobe-like stationary outgrowths of the edges of the tergite, from which the wings of the imago develop during the next molt).

Other parts of the body (mouth appendages, integuments and muscles of the body, internal organs) can also change significantly when shedding from larva to pupa, but these changes occur differently in different insects and can be insignificant.

Since for a considerable time before the molt on the pupa and after it the insect is unable to move (see above), in many insects the larva provides itself with a shelter before falling into the state of pronymph, which to some extent protects it from the attack of predators and adverse changes in the surrounding conditions. In the course of evolution, the ability to create such protective shelters arose independently in different taxa of insects, therefore, the devices of these shelters are diverse. Various insects use as shelters cocoons, houses, cradles or puparia.

Cocoons and doll houses

A cocoon is a protective formation that the larva makes from a silk thread before falling into the state of pronymph. The origin of silk in different larvae is different. The larvae of the taxon Panzygothoraca produce silk by the labial glands (which in most insects serve as the salivary glands) and secrete it through a hole in the region of the oral apparatus between the lower lip and the hypopharynx. Panzygothoraca includes Hymenoptera, Lepidoptera, Trichoptera, Scorpionfish (Mecoptera), Fleas (Aphaniptera) and Diptera. The larvae of many of them make silk cocoons; many hymenoptera, some butterflies and caddisfishes are especially dense cocoons. During the construction of the cocoon, they impose a silk thread on the inner surface of the cocoon under construction, manipulating the head for this (as can be seen in the photograph of Cimbex sp.). The cocoons of ants are popularly referred to as "ant eggs".

Unlike the larvae of Panzygothoraca, the larvae of double-backed beetles (Birostrata) produce silk by malpighian vessels , from where it diffuses through the intestinal epithelium into the lumen of the posterior intestine and is expelled through the anus. Accordingly, during the construction of the cocoon, the larva manipulates not the head, but a specially adapted for this purpose elongated flexible posterior end of the abdomen.

There are also cocoon wears, in particular, members of the genus Cionus (from the weevil family ( Curculionidae )) ^[6] .

Some insects do not build a cocoon of pure silk, but by adding grains of sand, soil particles, or fragments of plants. If a large part of the structure consists of such particles fastened together with silk, such a structure is called not a cocoon, but a doll house . Doll houses build many caddisflies (Trichoptera), butterflies, butterflies (Psychidae) and other insects.

Dollhouse crib

The larvae of some insects make a pupal crib ; unlike the cocoon, the cradle does not consist of the insect's silk, but of the particles of the surrounding material — soil, wood, etc.

Dendrophic larvae of many types of barbel and grinders do not leave the forage tree before pupation, creating cradles in special chambers in the thickness of the bark or wood . Such a camera is a continuation of the larval movement, which is blocked by drillmeal, from which another passage leads to the surface of the trunk, through which the beetle subsequently leaves the cradle. Different representatives of this course can open out or remain covered with a thin layer of bark. Before turning into a pupa, the insect is located in a chamber in a certain way with respect to the field of gravity: up or down with its head or lying horizontally - on the dorsal side. Some other dendrophagous beetles (for example, barbs of the genus Prionus ), before pupation, get out and build cradles from drilling flour and soil not far from their forage tree ^{[7] [8]} .

Puparium

У некоторых насекомых куколка защищена не созданным ею сооружением, таким как кокон, домик или колыбелька (см. выше), а её собственной личиночной кутикулой, претерпевшей определённые изменения. Такая оболочка из личиночной кутикулы называется пупарий (puparium), то есть вместилище для куколки (pupa). В этом случае при линьке с личинки на куколку старая личиночная кутикула не сбрасывается после того, как она отслоится от гиподермы, а поверх гиподермы сформируется новая куколочная кутикула. Вместо этого личиночная кутикула вздувается и затвердевает, образуя плотную защитную оболочку вокруг куколки. Поскольку пупарий образован личиночной кутикулой, он имеет те же детали внешнего строения, что и личинка, но по пропорциям, общей форме, цвету и твердости может существенно отличаться от личинки.

Пупарии свойственны круглошовными мухам (Cyclorrhapha), мухам-львинкам (Stratiomyidae) и веерокрылым (Strepsiptera).

Иногда пупарий неверно называют «куколкой» и рассматривают как одну из форм куколок наряду со склеенными (т. н. «покрытыми») и несклеенными куколками. На самом деле, в отличие от куколки, под кутикулой пупария имеется ещё одна кутикула — кутикула истинной куколки. В отличие от пупария, находящаяся в нём куколка имеет все части внешнего строения, характерные для куколки — ноги, антенны и ротовые придатки, сходные с имагинальными, протоптероны и др.

Иногда «пупарием» неверно называют личинку последнего возраста у белокрылок (Scytinelytra, или Aleyrodina), под кутикулой которой происходит формирование имаго. Это неверно, поскольку у белокрылок вообще нет стадии куколки или нимфы: под отслоившейся личиночной кутикулой белокрылки находится не куколка, которая была бы покрыта куколочной кутикулой, а развивающееся имаго, кутикула которого ещё не образовалась.

• Pupa photos plus species descriptions at Insecta.pro
• Silk worm life cycle photos