Flies, Gnats, and Mosquitoes Brian V Brown, Natural History Museum of Los Angeles County, Los Angeles, CA, USA r 2001 Elsevier Inc All rights reserved This article is reproduced from the previous edition, volume 2, pp 815–826, r 2001, Elsevier Inc Glossary Diptera Group of insects to which the flies, including gnats and mosquitoes, belong Introduction The insect Order Diptera, with more than 124,000 currently described, extant species, ranks as one of the worlds largest groups of organisms Along with the other insect megadiversity groupsFColeoptera (beetles; 350,000 species), Lepidoptera (butterflies and moths; 120,000 species), and Hymenoptera (ants, bees, wasps, and sawflies; 130,000 species)Fthey form the largest aggregation of species on the planet Each of these megadiversity groups has more species assigned to it than to any other group of organisms except plants (300,000 species) Like other insects, most species of Diptera are still undescribed, and the actual number could range as high as million or more species Diptera are found on every continent, including Antarctica The relative percentage of Diptera within the insect fauna rises with latitude (and elevation) as other, less cold-adapted taxa are lost; for instance, over one-half of all insect species recorded from the Canadian high arctic are Diptera The extant species of all biogeographical regions have been cataloged (Table 1), as have the fossil Diptera Some catalogs are badly outdated and the number of species described for each region is often more indicative of the amount of taxonomic activity directed at a given fauna than the true diversity For instance, the Palearctic Region is the best studied and has more described species than the relatively poorly known, but presumably more diverse, Neotropical Region Therefore, conclusions about dipteran biogeography based on these numbers will be highly inaccurate Diptera are a well-established monophyletic group, with the most obvious defining character being the reduction of the hind wings to small, club-shaped organs called halteres The Table Biogeographical regions and the number of described diptera species Region Number of species Nearctic Neotropical Palearctic Afrotropical Australasian Oriental Antarctica 25,000 20,000 29,000 16,318 15,764 15,964 60 Compiled from the various catalogs 488 Larva (pl larvae) Immature stage of flies, often called maggots insect orders considered to be most closely related to Diptera are Siphonaptera (fleas) and Mecoptera (scorpionflies), although recent molecular research indicates that the highly aberrant Strepsiptera (twisted-wing parasites) may be their closest relatives Fossil Diptera are common in the amber faunas of the world, which however extend back in time only to the early Cretaceous The oldest dipteran fossil is believed to be from at least the mid-Triassic Like the other megadiversity groups, the Diptera are holometabolous insects, with a separate egg, larva, pupa, and adult stage Generally, most feeding takes place in the larval stage, whereas the adult is usually specialized for reproduction and dispersal Some adult Diptera are voracious feeders, however, requiring substantial supplemental feeding to mature their eggs or power their flight Flies are common in natural, disturbed, and urban habitats Larvae are found on land and in freshwater; there are relatively few marine or brackish water species Some species are synanthropic and have been transported around the world with human activities Diptera are the most important vectors of human and animal disease, and a few plant-feeding species have become agricultural pests The life history of most species of flies, however, is unknown The group is so large, and there are so many undescribed species, that the science of dipterology is still in its relative infancy Major Subdivisions Table presents a general list of the families of Diptera and some of the higher taxa that contain them This list is based on only one of several possible classifications, however, and cannot be considered the final word in dipteran groupings Common names, where well established, are given in Table Many families lack common names, including the second largest family in the order (Tachinidae) That a group with more described species than the mammals lacks a common name is a good indication of the lack of general appreciation for the importance and ubiquity of the Diptera The number of described species in each family is given, but in many instances these numbers are badly out of date and should be considered a bare minimum Certainly, in most families of Diptera there are a large number of undescribed species awaiting the attention of specialists It is estimated that we Encyclopedia of Biodiversity, Volume http://dx.doi.org/10.1016/B978-0-12-384719-5.00167-2