Hemiptera

Taxobox | name = Hemiptera|

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image_caption = "Acanthosoma haemorrhoidale", a shield bug
image_width = 240px

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image2_width = 240px
image2_caption = Aphids
regnum = Animalia
phylum = Arthropoda
classis = Insecta
ordo = Hemiptera
ordo_authority = Linnaeus, 1758
subdivision_ranks = Suborders [ITIS|ID=103359|taxon=Hemiptera]
subdivision =
Auchenorrhyncha

Coleorrhyncha

Heteroptera

Sternorrhyncha

Hemiptera is an order of insects, comprising around 80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others, collectively known as the true bugs. They range in size from 1 mm to around 15 cm, and share a common arrangement of sucking mouthparts [cite web |url=http://www.ento.csiro.au/education/insects/hemiptera.html |title=Hemiptera: bugs, aphids and cicadas |publisher=CSIRO |accessdate=2007-05-08] .

Characteristics

The defining feature of hemipterans is their possession of mouthparts where the mandibles and maxillae have evolved into a proboscis, sheathed within a modified labium to form a "beak" or "rostrum" which is capable of piercing tissues (usually plant tissues) and sucking out the liquids — typically sap.

The name "Hemiptera" is from the Greek "hemi" ("half") and "pteron" ("wing"), referring to the forewings of many hemipterans which are hardened near the base, but membranous at the ends. These wings are termed "hemelytra" (singular: "hemelytron"), by analogy with the completely hardened elytra of beetles. They may be held "roofwise" over the body, or held flat on the back, with the ends overlapping. The hindwings are entirely membranous and are usually shorter than the forewings.

The antennae in Hemiptera are typically five-segmented, although they can still be quite long, and the tarsi of the legs are three-segmented or shorter [cite web |url=http://eny3005.ifas.ufl.edu/lab1/Hemiptera/Hemiptera.htm |title=ENY 3005 Families of Hemiptera |author=John L. Foltz |date=2003-01-23 |publisher=University of Florida] .

Although hemipterans vary widely in their overall form, their mouthparts (formed into a "rostrum") are quite distinctive; the only orders with mouthparts modified in a similar manner are the Thysanoptera and some Phthiraptera, and these are generally easy to recognize as non-hemipteran for other reasons. Aside from the mouthparts, various insects can be confused with hemipterans, including cockroaches and psocids, both of which have longer many-segmented antennae, and some beetles, but these have fully-hardened forewings which do not overlap cite book |author=Michael Chinery |title=Insects of Britain and Northern Europe |edition=3rd edition |publisher=Collins |date=1993 |id=ISBN 0-00-219918-1] .

Classification

The present members of the order Hemiptera were historically placed into two orders, Homoptera and Heteroptera/Hemiptera, based on the differences in wing structure and the position of the rostrum. These two orders were then combined into the single order Hemiptera by many authorities, with Homoptera and Heteroptera classified as suborders. The order is presently more usually divided into four or more suborders, after it was established that the families grouped together as "Homoptera" are not as closely related as had previously been thought (see paraphyly). Auchenorrhyncha contains the cicadas, leafhoppers, treehoppers, planthoppers, and froghoppers. The 12,500 species in the suborder Sternorrhyncha are the aphids, whiteflies and scale insects. The suborder Coleorrhyncha (comprising the single family Peloridiidae), contains fewer than 30 species of Gondwana-distributed bugs, and is sometimes grouped with the Heteroptera (to form the suborder Prosorrhyncha). Heteroptera itself is a group of 25,000 species of relatively large bugs, including the shield bugs, seed bugs, assassin bugs, flower bugs and the water bugs (see below).

The closest relatives of hemipterans are the thrips and lice, which collectively form the "Hemipteroid Assemblage" within the Exopterygota subclass of the Class Insecta [cite web |url=http://tolweb.org/Hemipteroid_Assemblage/8242 |title=Hemipteroid Assemblage |publisher=Tree of Life Web Project |year=1995] .

Life cycle and ecology

Hemipterans are hemimetabolous, meaning that they do not undergo metamorphosis between a larval phase and an adult phase. Instead, their young are called nymphs, and resemble the adults to a large degree, the final transformation involving little more than the development of functional wings (if they are present at all) and functioning sexual organs, with no intervening pupal stage as in holometabolous insects. Hemiptera is the largest insect order that is hemimetabolous; the orders with more species all have a pupal stage (Lepidoptera, Coleoptera, Diptera and Hymenoptera).

Many aphids are parthenogenetic during part of the life cycle, such that females can produce unfertilized eggs, which are clones of themselves.

Most hemipterans are phytophagous, feeding on plant sap, such as aphids, scale insects and cicadas. Most of the remainder are predatory, feeding on other insects, or even small vertebrates. A few, however, are parasites, feeding on the blood of larger animals. These include bedbugs and the kissing bugs of the family Reduviidae, which can transmit potentially deadly "Trypanosoma" infections cite web |url=http://www.nhm.ac.uk/nature-online/life/insects-spiders/fathom-bugslife/assets/26feat_its_a_bugs_life.pdf |title=Hemiptera: It's a Bug's Life |publisher=Natural History Museum |author=Jon Martin & Mick Webb |year=] .

Several families of Hemiptera are "water bugs", adapted to an aquatic lifestyle, such as the water boatmen and water scorpions. They are mostly predatory, and have legs adapted as paddles to help the animal move through the water. The "pondskaters" or "water striders" of the family Gerridae are also associated with water, but use the surface tension of standing water to keep them above the surface; they include the genus "Halobates" which is the only group of insects to be truly marine .

Economic significance

Many species of Hemiptera are significant pests of crops and gardens, including many species of aphid (such as whitefly, greenfly and blackfly) and various scale insects, including the cottony cushion scale, a pest whose infestation of American "Citrus" crops sparked one of the earliest biological pest control programmes, when the Australian beetle "Rodolia cardinalis" was introduced as a natural enemy of the scale insect [Cite web |url=http://gardenbees.com/biological%20control/revolution.htm |title=Cottony cushion scale: The pest that launched a revolution in pest control methods |date=2003-08-10 |author=David L. Green] .

Conversely, some predatory hemipterans are themselves biological pest control agents, such as various nabids [http://www.entomology.wisc.edu/mbcn/kyf402.html] and even some members of families that are primarily phytophagous, such as the genus "Geocoris" in the family Lygaeidae [http://www.nysaes.cornell.edu/ent/biocontrol/predators/geocoris.html] . Other hemipterans have positive uses, such as in the production of the dyestuffs cochineal and crimson, or shellac.

* See also Use of DNA in forensic entomology

References