Hemiptera

Specimen of the order Hemíptera. Source: Thomas Bresson [CC BY (https://creativecommons.org/licenses/by/3.0)]

Hemíptera is an order that belongs to the class insecta of the phylum Arthropoda. They are characterized by presenting two pairs of very noticeable wings that, in some species, are hardened.

This order was first described in 1758 by the renowned Swedish naturalist Carlos Lineo. Hemiptera encompass a wide variety of species, their exact number being unknown. It is estimated that there are approximately 85,000 described species, but specialists consider that there are still many more undiscovered.

This group of insects has been widely studied, since many of their species are known vectors for fearsome diseases such as Chagas disease or they constitute care pests for many crops.

General characteristics

– Hemiptera are a group of insects that belong to the Animalia kingdom and, as such, are multicellular eukaryotic organisms.

– They are triblastic animals because during their embryonic development they present the well-known three germ layers: endoderm, mesoderm and ectoderm. From them develop the different tissues and organs that will make up the adult animal.

– They are coelomed because they have an internal cavity called coelom. They have bilateral symmetry because by drawing an imaginary line along the longitudinal plane of the animal, two exactly equal halves are obtained.

– In this group of insects it is appreciated that most are dioecious, that is, the female and male sex are separated. Its reproduction is sexual, with internal fertilization and indirect development.

– They are animals that inhabit terrestrial, aquatic and semi-aquatic ecosystems. In the following video you can see a species of this order ( Nezara viridula ):

Taxonomy

The taxonomic classification of hemiptera is as follows:

-Domain: Eukarya

-Animalia Kingdom

– Phylum: Arthropoda

-Subphylum: Hexapoda

-Class: Insecta

-Subclass: Pterygota

-Order: Hemiptera.

Morphology

External anatomy

As with all arthropods, hemipterans have a body divided into segments: head, thorax, and abdomen.

Head

Generally, the head is small compared to the rest of the body. He also has little mobility.

The most striking elements of the head are the eyes, which in most species are compound; and the antennas, which are thin and have between 5 and 10 joints (segments).

At the front of the head is the animal’s mouthpart, also known as the beak. They have jaws and maxillae, which are covered by a kind of hood known as the lip. The elongated shape of the mouthpart provides the insect with the ability to suck blood from its hosts or the sap of some plants.

Chest

It is made up of three segments: metathorax, prothorax and mesothorax. It is in this part of the body that the scent glands are located, in the species that possess them.

The thorax is also the point of origin for the animal’s legs. These are three pairs that are made up of five joints, which are, from distal to proximal: tarsus, tibia, femur and trochanter. Depending on the lifestyle and habitat of the animal, the legs can present modifications and be adapted to different functions.

Specimen of Hemíptero. Hardened wings can be seen. Source: Thomas Bresson [CC BY (https://creativecommons.org/licenses/by/3.0)]

The wings of the insect are also born on the thorax. Hemipterans have two pairs of wings. In some species, the anterior pair is hardened, either completely or partially. The hind wings are membranous.

Abdomen

The characteristics of the abdomen vary in each group of hemiptera. There are some in which there is no difference between the thorax and the abdomen. As well as there are others in which the abdomen is wide and is divided into segments.

In the abdomen there are a series of holes through which the air enters so that the gas exchange of respiration takes place.

The terminal portion of the abdomen has the reproductive structures. In the case of the males of some species, in the final part they have appendages made of chitin known as parameres, which serve to hold the female during the act of copulation.

Internal anatomy

Circulatory system

They present an open circulatory system, made up of a single artery, the aorta, which exits directly from the heart in the thorax and heads towards the head. The fluid that circulates is known as hemolymph and it is distributed throughout the body and tissues of the insect.

Nervous system

It is ganglionic. It has a ganglionic accumulation at the level of the head, which functions as a brain. From this a nerve cord emerges that crosses the entire body of the animal. Along this cord there are several nerve ganglia.

Respiratory system

The type of respiration of the Hemiptera is tracheal. Your respiratory system is made up of a series of thin tubes called tracheas that branch internally. It is in them that the gas exchange takes place.

Digestive system

As in all animals of the insect class, the digestive system of the Hemiptera is made up of three parts: mesodeus, stomodeus and proctodean. The initial part of the digestive system (stomach) is made up of the crop, the esophagus and the proventriculus.

The intermediate part (mesodeo) is made up only by the intestine that does not have gastric cecum. Finally, the last portion (proctodean) flows outside, to release the substances that were not used during the digestion process.

Habitat and distribution

The insects of this order are widely distributed throughout the world geography. According to specialists in the area, they are much more abundant in the North American and European continents, however, a great variety of species are also known in other parts of America, as well as in Africa and Oceania.

Regarding the habitat, these insects can be located both on land and in water. 

In the case of insects that live in terrestrial environments, these are mainly found in the soil or on plants. They can be found under rocks or litter, as well as inside tree trunks.

In turn, the hemiptera that live in aquatic environments have managed to develop certain adaptations, such as the modification of some of their legs into structures similar to swimming paddles to be able to move through the water.

Despite living submerged in water, they require oxygen to breathe, so they make periodic ascents to the surface to capture it.

There are also species that live in semi-aquatic environments, which means that they live permanently on water or require it to survive. For this they have long and thin legs and antennae that allow them to move across the surface of the water.

Classification

The order Hemiptera is quite broad and in turn includes several suborders. Here are some of them:

Sternorrhyncha

Whiteflies, family Aleyrodoidea

It is made up of species that have proven to be fearsome pests for different types of agricultural crops. Within this suborder are insects such as aphids and whiteflies. In turn, it includes five superfamilies: Aleyrodoidea, Aphidoidea, Coccoidea, Phylloxeroidea and Psylloidea.

Heteroptera

Pirate bug (Anthocoridae), family cimicomorpha

The distinctive characteristic of this suborder is that its members have partially hardened forewings, the apical part of these being membranous and fragile. It is found in all habitats, as it includes aquatic, semi-aquatic and terrestrial insects.

It includes a total of seven infraorders: Enicocephalomorpha, Dipsocoromorpha, Neomorpha, Leptopodomorpha, Cimicomorpha and Pentatomorpha.

Coleorrhyncha

Xenophyes rhachilophus, family Peloridiidae

They have a very small lumpy-looking body (up to 4 mm in length). They are very old, since their origin dates back to the supercontinent Gondwana that existed millions of years ago. It encompasses a single family: Peloridiidae.

Auchenorrhyncha

Neotibicen linnei, Cicadomorpha family

The main characteristic of the members of this infraorder is that, when they flap their wings, they generate a characteristic sound. Likewise, specialists have been able to determine that these insects communicate through infrasound.

It is a very large group that includes two infraorders: Cicadomorpha and Fulgoromorpha.

Biological cycle

Reproduction

Hemiptera reproduction is sexual, with internal fertilization, indirect development and they are oviparous.

Before coupling occurs between individuals of different sexes, the female releases chemical substances known as pheromones into the environment, which have the function of acting on the opposite sex by attracting them.

For the reproductive process, the male introduces his copulatory organ into the female’s body and deposits the sperm in her. In some species this occurs through a spermatophore.

The time that elapses between fertilization and egg laying is variable. It can be of a few days or more, since it will depend on if the species is wintering or not.

During the biological cycle of insects belonging to the order Hemiptera, several stages are observed, such as: egg, larva (with several stages) and adult or imago.

Eggs

Starting the life cycle with the egg, it can be said that the female puts them in places where they are protected, such as on the ground, covered by remains of dry leaves or by any other element that is nearby and that the female can use for this purpose.

Likewise, each species has its peculiarities when it comes to eggs. These, of variable number, can be put in groups or in isolation. In the first case, it is possible that the female secretes some type of substance, whose function would be to keep the eggs physically united and together, forming a kind of compact structure.

Hemiptera eggs and larvae. Source: böhringer friedrich [CC BY-SA (https://creativecommons.org/licenses/by-sa/2.5)]

However, the eggs are not always unprotected, since there are species in which there is a marked tendency to parental care.

Regarding this there are numerous examples. For example, there are species in which the males are the ones who carry the piggyback and there are many others in which the female is the one who protects the eggs during their development period with her own body.

Larval stages

After the time required for the individual to form, it emerges from the egg. The vast majority of insects in this order hatch from the egg through the operculum. Most work their way through the different layers of the egg using pressure on them.

The individual that emerges from the egg is the first larval stage. After a short time, the first molt takes place. From here, the animal begins to feed, since during its first stage as a larva it does not.

Two successive molts occur. When the individual is in its third larval stage, the signs of what, in the future, will be the structures that will make up the adult begin to be observed. A representative example of this is the wings.

During molts 4 and 5, the wings are fully developed. The last molt of the Hemiptera is known as imaginal molt and results in an adult individual, whose wings are already fully developed. Here the reproductive structures are also formed, although they are not yet suitable for reproduction.

After a certain time has elapsed, the gonads are activated and the individual is already in full capacity to reproduce to give continuity to the cycle.

Feeding

Taking into account that the order Hemiptera is made up of a wide variety of insects, it is stated that their eating habits are just as varied. Among the members of this order you can see practically all the types of food that exist in the animal kingdom.

There are Hemipterans that are phytophagous and feed on plants. It can be from some part of the plant, such as the stem, leaves or flowers, as well as from substances that are inside it, such as sap.

Similarly, there are also Hemipterans that have carnivorous habits. These feed on other insects. This type of hemiptera is very important in some ecosystems, since they contribute to control the population levels of certain species that, in some cases, constitute pests for crops.

Finally, there is a small group of Hemiptera that feed on the blood of other animals, especially mammals and certain birds. These types of insects are known as hematophages. These hemiptera are of great scientific interest, since in most cases they constitute vectors of certain disease-causing agents.

Examples of species

Aleurocanthus spiniferus

Aleurocanthus spiniferus

It is a hemiptera that belongs to the Sternorrhyncha suborder, specifically the Aleyrodiidae family. It is characterized by a prominent mustard yellow abdomen and two pairs of large wings. It is also an important pest of orange and tea plants.

Graphocephala coccinea

Specimen of Graphocephala coccinea. Source: Bruce Marlin [CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)]

It is native to North and Central America, specifically from southern Canada to Panama. Among its most outstanding characteristics are its vibrant colors that allow it to be easily distinguished. This species of hemiptera is a vector for the bacterium Xylella fastidiosa , which causes serious damage to plants such as oak and elm, among others.

Scutiphora pedicellata

Scutiphora pedicellata

It is a hemiptera, a member of the Scutelleridae family. It has a characteristic very colorful appearance, green in color, with beautiful orange ornaments, as well as black spots on its back. It is oval in shape and can reach a length of up to 1.5 cm.

Halyomorpha halys

Halyomorpha halys

It is an insect member of the Pentatomidae family. It is found in the Asian continent, specifically Japan, Taiwan, China and the Korean peninsula. They do not measure up to 2 cm and among its distinctive elements is the disgusting smell it gives off, the product of the action of glands found in its abdomen and thorax.

Aelia acuminata

Aelia acuminata

It is a hemipteran insect belonging to the suborder Heteroptera, specifically the Pentatomidae family. Its body has very distinctive yellow and black stripes that are arranged longitudinally.

This insect constitutes a pest for cereal crops. It is distributed mainly on the African continent and Europe.

Panstrongylus geniculatus

Panstrogylus geniculatus

This insect belongs to the suborder Heteroptera, family Reduviidae. It is widely known for being the vector of the protozoan Trypanozoma cruzi, which causes the disease known as Chagas disease.

It is typical of the American continent, being distributed from southern Mexico to Argentina. It has an elongated body, with characteristic black spots on its back.

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