Nematocera Brachycera Species Table

INTRODUCTION TO DIPTERA

Diptera is the name given to true flies, the name means two wings and it is this feature which differentiates them from other types of fly such as mayflies and alder flies which have four wings. In Diptera the hind wings have become reduced to a pair of small knob-like structures called halteres. The function of these halteres is to maintain stable flight by signaling to the brain the flies spatial orientation. This is achieved by small groups of campaniform sensilla which detect mechanical stress imposed upon the cuticle at the base of the vibrating halteres. The fly can then compensate for any change in orientation.

Diptera are be divided into two suborders, the Nematocera, and the Brachycera. These two suborders can be distinguished morphologically by wing veination and antennal type in the adult forms, and by ecological habitats.

The Nematocera includes many important species from both a medical and veterinary viewpoint. The mosquitos, blackflies (Simulium spp) and biting midges are included in this suborder. Adults of this suborder generally have antennae composed of elongated segments numbering six or more giving these flies long filamentous antennae. Most flies in this suborder are only a few millimeters in length and can be classed as delicate in structure.

The Brachycera are characterized by having a annulated terminal segment on their three segmented antennae. Annulate means that there are circular constrictions along the length of the segment giving the appearance of many small separate segments. These flies are usually quite large, 5-20mm or more and relatively heavily built. In this suborder are horse flies and deer flies. The Cyclorrhapha used to be classified as a seperate suborder but is now grouped with the suborder Brachycera, generally classed as the higher flies. Adult flies of this suborder can be distinguished by arista on the terminal segment of their three segmented antennae. Arista are bristle like structures and they are found on the upper dorsal surface of a projection on the terminal segment of the antennae. The abdomen of higher Brachycera rarely shows the seventh segment as visible. Wings generally have less veinatation than the Nematocera and lower Brachycera. In the blood feeding forms a hard inflexible proboscis projects from the lower part of the head. This feature shows that the name biting flies is not entirely accurate as most pierce and suck rather than bite. This fact is true of Nematocera as well.

All Diptera belong in the division Holometabola meaning complete metamorphosis, going from egg-larva-pupa-adult. Diptera usually exhibit four larval stages although in many Cyclorrhapha only three are visible as the fourth larval stage develops within the exuvium (hardened cuticle) of the third larval stage. The exuvium when hardened is usually a dark rusty brown colour and is termed the puparium. Most Nematocera and Brachycera have aquatic larvae, whilst many Cyclorrhapha have puparium which develop in soil after dropping off their food source. When the young adult emerges it must dig its way to the surface. To enable this certain species have a ptilinum and a open front suture on the head capsule. The ptilinum is a balloon like structure that is inflated and expands through the suture in the head to push away the soil in front of the fly. When deflated the young fly is able to move into the space created and the procedure is repeated until the fly emerges. The suture is then closed with the ptilinum withdrawn. Due to being haematophagous biting flies are a very important group due to economic losses they cause to livestock. Apart from the blood lost to the feeding fly many pathogenic organisms are transmitted. This is especially apparent with mosquitos which transmit various arboviruses, blackflies which transmit Onchcerca linealis and O. gutterosa which are cattle nematodes, and tsetse fly which transmit trypanosoma.