Diptera

“One single infected mosquito that escapes can go on to bring death to dozens of victims in its lifespan, lay more eggs and restart an outbreak that progresses from a few to dozens to hundreds.” – T.K Naliaka.

The Diptera (“true flies”) are an order of insect that contains around 120,000 species. They are characterised by possessing only 1 pair of wings, with the hindwings reduced into halteres (gyroscopes). Whereas flies have a reputation for being ‘dirty’ and transmitting diseases, members of the true flies are beneficial as pollinators, predators, parasites and to processes of decomposition.

IMPORTANCE. Flies are hugely important for agriculture and disease transmission. Crane flies are root-feeding pests of grasses, fungus gnats attack cultivated mushrooms and gall midges attack cultivated plants. Medically important flies include black flies (blood-feeding), biting midges (vectors of blood-borne diseases), sand flies (vectors of leishmaniasis) and mosquitoes which are vectors of malaria, yellow fever, dengue, encephalitis and filariasis. Some flies as beneficial as they are predatory on pest species or are parasitic (tachinid fly).

CLASSIFICATION. Diptera is usually divided into the sub-orders; Nematocera, Brachycera and Cyclorrhapha (but is sometimes include in Brachycera). Nematocera are the “thread-horned flies”, which refers to the long, slender antennae. Nematocerans are delicate insects with long legs, usually with aquatic larvae (with well developed head capsule) and they include craneflies, gnats, midges and mosquitoes. The Brachycera are the “short-horned flies”, due to their short antennae (fewer than 8 antennal flagellomeres). Larvae have a reduced head capsule, a reduced retractile head (hemicephalous) and adults are well-built with compact bodies. Examples of brachycerans include horse flies, soldier flies, bee flies and assassin flies. The cyclorrhapha (“higher-flies”) are the largest division and include the fruit flies, house flies, blow flies, bluebottles, flesh flies and warble flies. Antennae are short and larvae have no distinct head capsule (acephalous).

Asilidae, robber fly

IDENTIFICATION. Characters used include wing venation, antennae, legs, chaetotaxy (arragement of bristles), head and thoracic sutures and body size. Nematocerans can be identified by their antennae usually having 6 or more segments to it, and the brachycerans have very short antennae. The cyclorrhapha usually have 3-segmented antennae with large hairs arising dorsally near middle of the third segment.

FLIGHT. The muscles operating the wings in true flies are not attached directly to the wing bases (as in more primitive fliers) but the muscles alter the shape of the highly elastic thorax, and rapid oscillations of the thoracic componenets are translated into wing motion (1000 wing beast per second). The flight systems in the true fly allow a phenomenal degree of aerial agility, allowing dipterans to hover, fly backwards, turn 360 degree angles and fly/land upside down. The gyroscopes (halteres) beat to provide the fly with sensory information, and advanced vision in true flies (fast movement detectors) allow them to react to avoid collisions and change direction very fast with super-fast reflexes. New research suggests the visual information from the compound eye is sent directly to the wing muscles and halteres, allowing the flight stabilizers to be fine-tuned by images from the eyes.

 

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