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OVERVIEW OF INSECTS
Translate into English by Dr. Phan Quoc Toan
I. General of Entomology
The specific term Entomology is derived from Greek words éntomonand Logia, meaning “Insects” and “Science”. Entomology is a scientific study of insects. In the past the term “insect” indicated the study of terrestrial invertebrates animals or other arthropod such as arachnids, earthworms, land snails… Until the middle 19th centuries, Entomology was defined to the insects (Class Insecta) of phylum Arthropoda.
Insect is the most diverse group of animals. They have a variable and complete life cycle. The larvae hatch from eggs, developing to the adults by several of molts. Many species spend at least part of their lives under water, larvae or adult stage (aquatic insects).
Insects body are organized into three distinct units: a head, a thorax and an abdomen. The head supports a pair of sensory antennae, a pair of compound eyes, and one to three simple eyes. Mouthparts is highly variation, modified according to their diet. The thorax possess three pair of legs, and none, two or four wings. The abdomen consists of eleven segments but in some species, those segments are fused together or reduced in size. In the territorial insects, they respire by using a system of internal tubes which openings on the sides of the abdomens called spiracles. The excretion is Malpighi tubules. The development of insects is undergone by metamorphosis. In the complete metamorphosis, insects changes into four stages (egg – larva – pupa – aldult) whereas lacking the pupa stage in the incomplete metamorphosis. The nymphs in the incomplete metamorphosis is similar in appearance to aldult insects.
Many insects are beneficial to the environment and to humans such as pollinate flowering plants, feed on other insects which damage to agriculture and human structures; some insects could be also used as medicine. However, many insects are very dagerous to the human health and society, such as transmit diseases or destroy argicultural goods...
II. Characteristics of insects
Diversity
At present about 1,2 million species of animals have been described in our plane. Among them, there are 1 miliion described species of insects. However, the true dimensions of species diveristy remain uncertain, estimates range from 6-10 milliion, potentially represent over 90% of the differing animal life forms on Earth.
Distribution
Insects have a widespread throughout from the equator, the North to South Pole, excluding in the oceans. In the high moutain with the elevation of 500m from the sea, we can find some stink bug species; larvae of some cicadas can living 2 meters underground or 36m in termites nets. It also can be found some insects in the hot course of water with the degree of 70-80. Eventually the larvae of some flies can living in the fish sauce which have a highly salty.
Density
According to a literature (author unknown), approximately about 250 million individuals insects of each person; and 12 million individuals insects in each one square kilometer.
Measurements
The measurement of insects is high variation. The smallest sized species is probably a parasitic bee of the family Mymaridae which have 0,21 mm of body sized length. The largest sized insects is probably belonging to a butterfly species (Thysania agrippina) from South America with wingspan about 30 cm or a fossil of dragonfly with wingspan about 50-70 cm. The largest sized species has about 1500-2500 times more the smallest ones while in case of mammals, the largest species (blue whale – Balaenoptera musculus has 30 m of the length) has 836 times more the smallest ones (a rodent species from Italy with body length is about 3,6 cm).
Reproduction
Insects produce a lot of eggs during its lifespan. A queen bee can lay 2000 eggs per days or the queen termite lay several millions eggs throughout her life. However, the lifetime of insects is short. For example, the house fly (Musca domestica) can lays 6 littersa year, from January to July with aproximately 120 eggs in each times. In the case of perfect condition with no individual was dead, that fly could produced 93 individuals after one year which would covered 50 cm of the surface of the Earth.
The characteristes of insects which help them benefit to vary habitats and very diversity as follow:
- Insects have a hard outer convering (exoskeletons) which well protect them from elements of environments.
- They are tiny or small size animals; requirement a small amount of food so they easy to obtain a suitable position in the ecosystem.
- Among the invertebrate animals, only insects is own their wings which help them have a widespread distribution.
- They adapt many kind of environments and having an extraordinary reproduction.
III. Taxonomy of insects
1. Classification for insects
Insects have a high variation of morphology but they also have a closely relationship of phylogeny. This could help us to devide them into separated groups called classification.
Classification for insects is study differential species to separating and determining their relationship and phylogeny. The classification for insects is based on the characters as follow:
The division
2. Clades of insect classification
- Species is a basis of the classification. They are the largest group of organisms have a similar morphology, scientific name and molecular phylogeny, two individuals are capable of reproducing fertile offspring, typically using sexual reproduction.
- Genus is a taxonomic rank above species. They are a group of some closely species.
- Family is a group of closely genera. A family may be divided into subfamilies, tribes, subtribes. The family names end with the suffix “idae” in animals and “aceae” in plants.
- Order is a group of closely families. There are about 28 orders of insects at present. The order names end with the suffix “les” in plants, and generally “ptera” in insects (excluded some orders such as Odonata of dragonfly or Mantodea of praying mantis). However, there is not an suffix ended for other groups of animal. Order can devided into suborders.
- Class is a group of closely orders. The scientific name of class insect is Insecta. The ended name of classes are variation among animals and plants. In algae is phyceae (for example, the family Bacillariophycea of Diatoms) and mycetes of mushroom (for example, the class Ascomycetes), but is opsida in the names of high rank plants (for example, the class Magnoliopsida of flowering plant). In the veterbrate animals, the names of class are different, such as Pisces (Class of fishes) or Amphibia (Class of frogs, salamanda...).
- Phylum is a group of closely Classess. It is a taxonomic rank below kingdom and above class. Insects are belonging to the phylum athropod animals (the invertebrate animals having an exoskeleton and segmented body).
- Kingdom is a group of closely Phylums. This is highest taxonomic rank of the classification of animal. The nomenclature of Kingdom have been changed during the development of taxonomic history. Firstly, Linnaeus (1753) devided the life into two basic kingdoms: Animal (Animalia) and plant (Plantae). Later Haeckel (1865) introduced a system with three kingdoms: Animal, Plant and Protista. The protista is a group of living organs in which having body whithin a cell. In 1969, Whittaker divided the life into five kingdoms: Prokaryota (includes Bacteria and Archaea), Protista, Fungi, Animal and Plant. Recently, in 1985, the International Society of Protozoloogist suggested dividing Protozoa from the kingdom Protista as a subkingdom of animal – it called Protozoa. At present, the researchers usually used the systems of six kingdoms (Animalia, Plantae, Fungi, Protista, Archaea/Archaeabacteria, and Bacteria/Eubacteria).
Although species is a smallest taxonomic rank in the system, they also have a high variation among individuals. The different between them are depending on the modification of environmental elements. Actually there is an taxonomic unit called subspecies subordinate to species. The subspecies are slightly different to main species in some characters of morphology and biological behavious and they are capable of interbreeding and producing fertile offspring.
The generation of a subspecies is depended on the environmental elements and natural selection. For example, subspecies bee from Caucaso (Armenia), Apis mellifera remipes Poll differs from the main species Apis mellifera L. by three first abdominal segments are red-yellow, non-biting human and only found from Caucaso. Therefore, subspecies is also called geographical clines.
The taxonomists created subspecies, subgenus, subfamily or superfamily besides the basic taxonomic units to understanding exactly their taxonomic relationship. However, in fact only species exist in nature. Other taxonomic units such as genera, families, orders... are established as a convention of taxonomy.
3. Nomenclature
Insects usually have two names: a common and a scientific names (or latin name). The common name of a species often vary from region to region where they are occurring. Some species may be have a same common name. Therefore, most literatures refer to species using their scientific name.
Scientific name, or Latin name, of a species is general using in the world. It is created by the Swedish natural scientist Carl Linnaeus and has two parts: The first part of the name identifies the genus (the first letter is Capital) to which the species belongs; the second part identifies the species within the genus. For example, the scientific name of leopard lacewing butterfly is Cethosia cyane.
The subspecies name has three parts in which the third part refers the name of that subspecies. For example, the swallowtail butterfly has scientific name is Papilio nephelus chaon.
At the end of a scientific name is often combine one or several researchers name who discovered that species with the years of publication. The genus and species names are italic while the authors name and the published year are normal. For example, the foreststream damselfly Protosticta spinosa Phan & Kompier, 2016.
If the author names and published year are in brackets that mean the original genus name given by the author is now considered to belong in a different genus. For example, in case of the Chetstnut Tiger butterfly Parantica sita (Kollar, 1844), Kollar described this species in the genus Danaisin 1844, but later the researchers transformed it into the genus Parantica.
It is difficult to estimate how many species of insects existing in our planet. Therefore, one of mission of Entomologists is studying diversity species and discovering new species from many locations of the world.
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