After the succession of molts, an insect reaches the final adult form and no further molt takes place.
Each developmental stage of an arthropod between molts is termed as Instar. For example, after hatching from egg, the hatchling is said to be first instar.
When the insect molts again, it is then a second instar and so on. There are four patterns of growth and development in insects namely Ametabolous, Paurometabolous, Hemimetabolous and Holometabolous.
It is the type of insect development in which there is no metamorphosis. The emerged immature stage appears very similar to adult except that it lacks sexual structures. It grows only in size by replacing its old skin through molting. The larva grows bigger and the genitalia develops progressively with each molt. The young one which emerges from egg resembles adult in miniature form, is called nymph. The reproductive organs are undeveloped in nymph and after molting the nymph becomes an adult.
Both forms i. This is the characteristic feature of Apterygotes e. For instance, the silverfish hatched from egg looks like an adult and undergoes subtle anatomical changes between molts Figure 1. Immature silverfish molts 6—7 times until it reaches sexually mature adult stage.
In favorable conditions, silverfish may typically continue to molt during its lifespan and molts 25—66 times [ 1 ]. Ametabolous development in Lepisma. Paurometabolous development is found in less primitive forms like cockroaches, grasshoppers, praying mantis and white ants.
In this type of development, the newly emerged young one closely resembles the adult in general body form, habits and habitat but many adult characters like wings and reproductive organs are not developed and their relative proportions of the body also differs. The young forms are termed as nymphs.
The wings develop as wing pads on second and third thoracic segments at an early stage and gradually increase in size during each successive molt. The external genitalia also develops gradually after each molt. These nymphs lead an independent life and attain adult features through several molts. There are three stages in the life cycle of these insects i. For instance in grasshoppers, before becoming adults the nymphs undergo 5—6 molts to change their body form Figure 2. The nymph stage is species specific and lasts for a period of 5—10 days depending upon the weather conditions like temperature and humidity.
Paurometabolous development in grass-hopper. In this type of development, adult form is attained by gradual morphological changes with successive molts. The hatched larva lacks wings and genitalia but have some other characteristic features which are absent in adult.
These features are lost at the final molt. The orders Plecoptera, Ephemeroptera and Odonata Figure 3 have aquatic larval stages. The young forms are known as naiads which are aquatic and respire by external gills but the adults are terrestrial in behavior.
Their life cycle also involves three stages: eggs, naiads and adults. When the naiads are ready to transform into adults, they come out of water and adult winged forms are released. The wings and genitalia develop externally but are not fully formed till adulthood. After the formation of wings no further molting takes place, only exception in mayflies where winged forms of aquatic nymphs come out and rest on trees to undergo final molting to become adults.
Hemimetabolous development in dragonfly. Complete metamorphosis is a kind of morphological change during post-embryonic transformation in which larva has no similarity with adult and there is always a pupal stage. Complete metamorphosis takes place in orders Coleoptera, Diptera, Hymenoptera and Lepidoptera. Pupal stage is the characteristic of holometabolous development i. In Order Lepidoptera moths and butterflies , the larva is known as Caterpillar Figure 4. It possesses a distinct head with powerful mandibles and three pairs of jointed thoracic legs.
The abdomen has four or five pairs of un-jointed, short abdominal legs which are termed as pseudo-legs or prolegs. These caterpillars eat voraciously and grow rapidly with several moltings. After completing four or five molts, the caterpillar is transformed into pupal stage. Holometabolous development in butterfly. In Order Diptera Houseflies and other flies , the larva is worm-like and devoid of appendages and is known as maggot Figure 5. The mature larva is about 12 mm long. The head is indistinct, with a pair of oral lobes and hooks.
Holometabolous development in housefly. In Order Coleoptera ground beetles, ladybirds and rove beetles , like adults the larvae referable to many beetle families are predatory in nature. The larval morphology is highly varied among species, with well-developed and sclerotized heads, distinguishable thoracic and abdominal segments and are known as grubs. In Order Hymenoptera bees and wasps , the larvae are grub-like with well developed head and mouthparts are of chewing type.
Larvae are generally apodous, rarely eruciform with locomotory appendages. The larvae in different orders of insects are known by different names i. The larvae are grouped into four types on the basis of development of appendages Figure 6. Protopod larva : In this type, larvae come out from the eggs which contain very little amount of yolk and this happens during the early stages of embryonic development.
There is no segmentation on the abdomen. The thoracic appendages and head cephalic are primitive in form e. Polypod larva : In this type, larvae have three pairs of thoracic legs and two to five pairs of abdominal prolegs.
Only prothoracic and abdominal spiracles are open in their respiratory system. Larvae of orders Mecoptera Scorpion flies and hanging flies and Lepidoptera butterflies and moths are of polypod type. On the basis of number and location of prologs, the lepidopteran larvae are further classified into three types: caterpillar, semilooper and looper.
Caterpillar: Caterpillar is the larval stage in Order Lepidoptera. It has soft body that can grow rapidly between molts. It bears five pairs of prolegs which are present on 3rd, 4th, 5th, 6th and 10th abdominal segments and three pairs of thoracic legs.
Semilooper: The semilooper larva bears three pairs of thoracic legs and three pairs of prolegs which are present on 5th, 6th, and 10th abdominal segments e. Looper: The looper larva have three pairs of thoracic legs and two pairs of prolegs present on 6th and 10th abdominal segments e. Oligopod larva : The body of the oligopod larva is well segmented.
It have three pairs of thoracic legs and possesses well developed cephalic appendages. The prolegs are absent. In some oligopod larvae, a pair of cerci or similar caudal processes is present. Head capsule is well developed and mouthparts are similar to the adult. On the basis of structure, the oligopod larvae can be further classified into two types viz.
Campodeiform type: The campodeiform larva has dorso-ventrally flattened and well sclerotized body which bears long thoracic legs and a pair of terminal cerci. This type of larvae is found in orders Neuroptera, Trichoptera, Strepsiptera and in some Coleoptera e. It bears short legs and terminal abdominal processes cerci are absent.
These larvae are less active and sluggish in nature. Scarabaeiform larvae are mainly in Scarabaeoidea and also in some other Coleopterans e. Apodous Larva : Thoracic legs or abdominal prolegs are absent in case of apodous larva and it has poorly sclerotized cuticle e. On the basis of degree of development of head, the apodous larvae can be further grouped into the following three types:.
Eucephalous Larva: In this type, larva has well sclerotized head capsule with relatively reduced cephalic appendages and is found in Nematocera Diptera , Cerambycidae Coleoptera and Aculeata Hymenoptera.
Hemicephalous Larva: In this type, larva has reduced head capsule that can be withdrawn within the thorax. It is found in families Tipulidae and Tabanidae of order Diptera. Acephalous Larva: This type of larva has no head capsule and cephalic appendages. Like larvae, the pupae are also of various types Figure 7. These can be grouped according to the presence or absence of functional mandibles which might be used by the adult to emerge from the cocoon or pupal cell.
The functional mandibles are present in decticous type of pupa, whereas in the adecticous type, the mandibles are not functional. The latter type can be subdivided into two: exarate and obtect. The exarate pupa has free appendages and the obtect have appendages glued to the rest of the pupal body.
An exarate pupa enclosed in a puparium is termed as coarctate whereas the silken protective case of obtect pupa is known as cocoon. Different types of insect larvae: a Caterpillar, b Semilooper, c Looper, d Campodeiform, e Scarabaeiform, f Eucephalous larva, g Hemicephalous larva, h Acephalous larva. Different types of insect pupae: a Decticous pupa b Adecticious pupa, c Exarate Adecticous pupa, d Obtect Adecticous pupa.
Heteromorphosis is the type of development characterized by radical change in forms between successive larval instars. The larval instars are pretty much similar in many endopterygotes. However, a larva experiences typical change in morphology and in habits during development in some families of orders Coleoptera Meloidae, Ripiphoridae , Diptera, Hymenoptera, Neuroptera and in all Strepsiptera.
It is common in parasitic and predaceous insects where change in habit occurs during course of development. The butterfly and moth develop through a process called metamorphosis. This is a Greek word that means transformation or change in shape.
Insects have two common types of metamorphosis. Grasshoppers, crickets, dragonflies, and cockroaches have incomplete metamorphosis. The young called a nymph usually look like small adults but without the wings. Butterflies, moths, beetles, flies and bees have complete metamorphosis.
The young called a larva instead of a nymph is very different from the adults. It also usually eats different types of food. There are four stages in the metamorphosis of butterflies and moths: egg, larva, pupa, and adult. Eggs are laid on plants by the adult female butterfly. These plants will then become the food for the hatching caterpillars. Eggs can be laid from spring, summer or fall.
This depends on the species of butterfly. Since dehydration is fatal to flea larvae, they will not survive relative humidity less than percent or soil temperatures greater than 95 degrees Fahrenheit.
However, if outdoor larvae will survive in cool, shaded areas and do very well in crawl spaces. In environments of suitable humidity and temperatures, fleas will develop year round. Flea larvae complete three larval instars stages and, depending on their environment, will range in length from about mm long. Flea larvae have no eyes and no legs. Their body is maggot-like and whitish, but turns progressively darker as the larvae feeds on feces excreted by the adult fleas.
Other than feces, larvae will feed on various types of organic matter such as food particles, dead skin, dead insects and feathers. Flea larvae do not take a blood meal directly from a host, unlike adult fleas. One of the last activities of flea larvae is to spin a silken cocoon and then enter the pupal stage. Controlling flea larvae usually involves using vacuums to remove, use of insect growth regulators and dust formulations that cause desiccation of the larvae.
Adult fleas begin searching for food when they emerge from the pupal stage. Females begin laying eggs right after their first mating, and both sexes will mate several times during their lives.
Adults in summer generations live from two to five weeks. Each year, the final generation of Monarchs, which emerges in late summer and early fall, has an additional job: to migrate to their overwintering grounds, either in central Mexico for eastern Monarchs or in California for western Monarchs. Here they survive the long winter until conditions in the United States allow them to return to reproduce.
These adults can live up to eight or nine months. Male and female Monarchs can be distinguished easily. Males have a black spot see photo on a vein on each hind wing that is not present on the female. These spots are made of specialized scales which produce a chemical used during courtship in many species of butterflies and moths, although such a chemical does not seem to be important in Monarch courtship.
The ends of the abdomens are also different in males and females, and females often look darker than males and have wider veins on their wings. No growth occurs in the adult stage, but Monarchs need to obtain nourishment to maintain their body and fuel it for flight.
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