Throughout their lives, insects experience a profound restructuring of the external and internal structure of the body. In other words, metamorphosis, characteristic of all animals. It’s just that it proceeds with characteristic and very specific features. Postembryonic development of an insect, as a rule, goes through three successive stages: egg, larva, imago. Many species have an additional stage: triungulin, pupa, etc.
Depending on how many stages of development an insect goes through, it can be classified into one of two large groups: with incomplete or complete transformation. Thus, the method of metamorphosis should be regarded as one of the main classification criteria.
From the article you will learn important features of the stages of insect development with complete and incomplete transformation, with hypermetamorphosis.
Biology
There is a division of the development cycle of synanthropic flies into four main phases: imago, egg, larva, pupa. Moreover, flies of certain genera are viviparous. These include Glossina and Wohlphahrtia. The development time of insects from egg to adult takes on average 20 days, but at higher temperatures the period can decrease to 6-7 days. This is primarily due to their heat-loving nature.
Development with incomplete transformation
Incomplete transformation is characterized by three stages of insect development: egg, larva and adult. A characteristic feature of this type of metamorphosis is the similarity of the appearance of the larva with the imago; like the latter, they have oral organs, compound eyes, and pronounced rudimentary wings. Moreover, a similar lifestyle is often observed. Insect larvae with incomplete metamorphosis are called nymphs.
This type of metamorphosis is observed in Orthoptera, Cockroaches, and Homoptera.
Larva
Having hatched, the larvae move deeper into the mass on which they were born. Depth may vary depending on temperature. That is, the lower it is, the deeper the larvae burrow. So, at a temperature of +12-17 degrees, they are most often located at a depth of about 20 centimeters. In warmer weather they can be found in the surface layers.
However, if the temperature reaches really high values, about 50 degrees, the larvae of synanthropic flies die. The intensity of development of larvae depends on the degree of aeration - this means that for full growth they need places with sufficient oxygen content. A comfortable humidity level of 60-80% is also necessary.
The intermediate stage of fly larvae is prepupae. This is a state of arrested growth. During this period, the larvae stop feeding and move to a cool place with a low level of humidity. This stage most often takes no more than a day.
Reproduction and development of insects
Insects are dioecious animals with internal fertilization
.
Often, differences in body size, shape and color are observed between males and females - sexual dimorphism
. For example, body coloring in dragonflies and blueberry butterflies, the upper jaws of the stag beetle's mouthparts, and the long antennae of male cockchafers.
Insects reproduce by laying fertilized eggs
. The eggs of different types of insects differ in shape, size and color. They can be white, green, yellow, red.
Larvae hatch from eggs
. The development of the larva can take place in a few hours or last for many months. For example, the cockchafer lays eggs in the soil, where the larvae develop for 4 years. And only after 4 years an adult beetle emerges from the soil.
Sometimes eggs develop without fertilization - parthenogenesis
(for example, aphids).
There are also viviparous insects
, from the body of which fully formed larvae immediately emerge. For example, blow flies, some types of aphids.
From the moment of birth or the release of an organism from an egg until the onset of sexual maturity, postembryonic development (or postembryonic development)
.
In insects, there are two types of postembryonic development: direct and indirect.
.
Direct development, or development without transformation (without metamorphosis)
, occurs without changing the external structure of the larva.
Indirect development
There are two types:
with partial changes (development with incomplete metamorphosis)
or
with significant or complete transformation (development with complete metamorphosis).
The nature of development depends on the degree of similarity or difference in the structure and lifestyle of the larva and the adult insect.
Direct development
characteristic of lower insects (springtails, campodea) and wingless parasitic insects (lice, bed bugs).
The eggs hatch into larvae that differ from adult insects only in their small size and underdeveloped genitals.
They have the same external structure and lead the same lifestyle. The development of larvae into adult insects is limited by growth with periodic molts. Outwardly they do not change.
In insects with incomplete metamorphosis
, for example, in grasshoppers and locusts,
larvae emerge from eggs, which are similar to adults in body shape,
feeding patterns and habitats.
The differences lie in the development of wing shapes and the ability to fly in adults. The larva feeds, periodically molts and grows quickly, and with each molt
its structure more and more corresponds to the structure of the adult.
Over time, it develops into an adult insect
.
Adult insects no longer grow
. This development is typical for many insects: cockroaches, dragonflies, bedbugs, aphids.
During development with complete metamorphosis
(for example, butterflies),
worm-like larvae emerge from the eggs
-
caterpillars
,
completely different from adult individuals
. Typically, such larvae have a larger number of segments than an adult, a different number of limbs (for example, caterpillars have abdominal legs, but butterflies do not), a different structure of the oral apparatus (caterpillars have a gnawing one, and butterflies have a sucking one with a proboscis). The larva's sense organs are less developed.
The larvae move, actively feed and significantly increase their size and weight. Having reached a certain age, they turn into a pupa. Doll
–
resting stage
(at this time the larva does not grow, does not move or feed).
The pupal stage is necessary so that major changes in the organization of the larva can occur (changes in the oral apparatus and body shape, the appearance of wings). an adult insect
emerges . The process of the butterfly emerging from the pupa usually takes about an hour. First, the legs come out of the pupa, then the mustache, the head, and only then the small wings and abdomen. Only after some time the wings will become natural sizes, become stronger, and the butterfly will be able to fly.
Development with complete metamorphosis is characteristic of the most highly organized insects
: beetles, butterflies, flies, mosquitoes and bees. This development is very useful, because larvae and adults differ in their habitats and feed on different foods. This reduces competition between them. For example, butterfly caterpillars feed on plant leaves, and butterflies suck nectar from flowers. Aquatic mosquito larvae feed on organic matter that they filter from the water, adult females are bloodsuckers, and males feed on nectar. May beetle larvae live in the soil and feed on plant roots, while adult beetles feed on tree leaves.
Thus, insects that develop without transformation (without metamorphosis) or with incomplete transformation have three stages of development: egg, larva and adult insect.
Insects that develop with complete metamorphosis have four stages of development: egg, larva, pupa and adult insect.
Insect larva
– stage of growth and nutrition. Often the larvae are inactive and have underdeveloped limbs.
Doll
– resting stage of body restructuring.
Imago (or adult insect)
– stage of reproduction and dispersal. Adult insects have well-developed limbs and wings.
Doll
The pupation process is carried out at an ambient temperature of +20-25 degrees, while the humidity should be from 20 to 40%, since the pupa does not tolerate high humidity. Therefore, such conditions are considered optimal for its development, which takes at least three days. The maximum permissible temperature for this stage of the insect is +43 degrees.
Flies that emerge from the puparia leave the soil, but do not immediately rise into the air. They sit motionless for about a minute, after which they begin to move quickly, pausing. Normal fly activity begins after 1.5-2 hours. Females emerge from clutches later than males - on average, by 12-24 hours. At the same time, the gender ratio is the same.
Development with hypermetamorphosis
The most difficult way for insects to develop is hypermetamorphosis. It is characteristic of some beetles (micromalthus, blister beetles, etc.), lacewings, buzz flies, and a number of hymenoptera.
During hypermetamorphosis, the larval stage of insect development occurs in several stages. There are strong differences in the structure and lifestyle of larvae of different ages. At the first stage, they do not feed, but at the same time they actively move and settle. The older larva, as a rule, lives in a specific habitat. She not only eats, but also grows. Sometimes, in order to move from one active form to another, a restructuring of the body is required. In these cases, the larva becomes motionless and stops feeding. A so-called “false pupa” is formed. Later, as, for example, in beetles from the Blister family, it turns into a real pupa, from which the beetle imago develops.
Imago
The lifespan of adult individuals is up to 20 days, in a passive state, in winter, up to 6-7 months. Adults can go without food for no more than two days, while young individuals can go a little longer. Flies become active at temperatures from +15 degrees. By activity we mean not only flying, but also eating.
The optimal temperature for flies in warm regions is +35 degrees, while in the middle zone it is 10 degrees lower. Although flies love light, oviparous females may seek out dark places. Typically, flies avoid low-light areas.
Flies are attracted to the smells of food, and females who lay eggs are happy to pay attention to ammonia vapors. Synanthropic flies use products as food, which can be food waste and excrement. This type of insect is particularly mobile.
Features of the structure of the imago
As mentioned above, the final stage of development of insects and some arthropods is the adult. What it is is easy to understand by referring to the original language. In some sources the term is translated as “true appearance” and this is true. Throughout their lives at this stage, adult individuals practically do not change; their development process stops. Most species do not molt. However, all rules have exceptions. Thus, lower orders (bristletails, springtails, etc.) periodically shed their cuticle even in the adult stage.
The main differences between adult insects and young individuals are as follows. They develop wings and genitals, antennae consist of a constant number of segments, and a certain type of oral apparatus is formed (often different from that of the larvae). The imago is maximally adapted to the environment, and this is expressed in adaptive mechanisms and many structural features: features of the respiratory system, body shape, development of sensory organs, additional protective mechanisms, etc.
For the vast majority of arthropods and insects, this phase is the peak of development. The only exceptions are some mites. For them, everything happens exactly the opposite. Parasitic species moving inside the body cavities and tissues of the host lose the morphological features inherent in the imago. This process is called dismaginization.
Zoophilic flies
A separate category of synanthropic flies that live in pastures and livestock farms are zoophilous. The main species of these insects, based on their veterinary importance, are three families: true flies Muscidae, as well as flies Calliphoridae and Sarcophagidae. Real flies can be blood-sucking or non-blood-sucking. The former actively parasitize animals, while the latter are more often found in residential areas.
Among the most dangerous representatives of zoophilic flies are Wohlfarth insects, the larvae of which attack small livestock and cause wolfharthiasis. This disease is expressed in the destruction of tissue by larvae using digestive enzymes and mouth hooks. The larvae eat living tissue and also contribute to the destruction of blood vessels. As a result, tissue inflammation occurs, which leads to suppuration and further development of gangrene.
Age-related color change
Hatching from the pupa and thereby undergoing the last molt in the larval stage, the insect leaves its shell. Often the initial color is light in tone (not white, but paler). Over a certain period (from several hours to 2-3 weeks), pigment substances accumulate and oxidize when in contact with atmospheric air, as a result of which the cuticle darkens.
Certain species, for example, the imago of butterflies (order Lepidoptera) appear with “their own” formed color.
The change in color may be associated with certain changes in the body. Thus, the desert locust is initially yellow-green in color. During the breeding season, reproductive enzymes accumulate in the body and as a result, the integument acquires a pink tint (pictured above).
What harm can synanthropic flies cause to humans?
Synanthropic flies can seriously harm the body. As adults, insects can be carriers of various infections. In particular, this is done by the ingress of pathogenic microorganisms into food or onto humans. Also dangerous are fly larvae that parasitize the human body and thereby cause myiases in tissues and cavities.
Three categories of pathogens are known:
- Random. The larvae enter the human body by consuming food that is contaminated. They live in the intestines for a certain period of time, causing cavitary myiasis.
- Optional. These are optional pathogens, the process of reproduction of which is carried out in spoiled products of animal origin. Under certain circumstances, adults can lay eggs in wound sites.
- Obligate. They are obligate pathogens, that is, species whose larvae are capable of growing exclusively in living animals.
Flies can transmit foodborne diseases because they feed on animal corpses and meat that is stored in direct violation of sanitary standards. Subsequently, they transmit the pathogens of these diseases. It is not uncommon for insects to cause infectious conjunctivitis and trachoma. This is possible if flies use discharge from the eyes of a patient as food, and then come into contact with the eyes of a healthy person.
Main function of the adult stage
So, the final stage of insect life is the imago stage; you have already learned above what this is. Having understood the essence of the definition, having learned the main features of the structure, it is easy to guess what is the main function of this phase. In adulthood, absolutely all organisms, by reproducing, maintain the population of the species. If among insects the number of oviparous females exceeds the number of males, then they are fertile. For example, a queen bee can lay up to 1,500 eggs per season.
The adult stage is important in terms of species dispersal. This process is facilitated by the presence of developed wings and limbs in adults.
Touching upon the general biological significance of the imaginal stage, it should be pointed out that the imago is a unique manifestation of evolutionary processes associated with the development of land by arthropods and their subsequent strengthening in occupied ecological niches.
What measures exist to combat synanthropic flies?
Insects can be controlled both through prevention and through extermination measures. When carrying out prevention, in order to avoid a further increase in the number of flies, it is necessary to implement the following steps:
- Regular removal of household waste.
- Providing paved areas for waste containers.
- On poultry and livestock farms, floors must be concreted and sewage drains must be installed. It is also necessary to install systems for flushing them with water.
- Installation of window mesh in the summer.
- Compliance with sanitary standards at food industry enterprises.
The destruction process involves the use of mechanical or chemical methods. The first involves thoroughly cleaning the room, catching flies in special traps, and using protective nets. This is an auxiliary method of control, as it does not provide complete protection, but only reduces the number of insects.
Chemical methods are much more effective, since their goal is the complete extermination of not only adult flies, but also their larvae and pupae. Various larvicides are used for this purpose. They are presented in the form of emulsions based on substances that may belong to different chemical classes. Adults are destroyed using insecticides and poisoned baits. Given the resistance of flies, food poisoned baits are most often used.
