An Introduction to Medical Entomology
For educational purposes.
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[See: Tabanidae Key]
Most adult "horseflies" are bloodsuckers, with females of most species feeding during the day. The larvae are mostly aquatic or semi aquatic, feeding on various kinds of animals occurring in the medium in which they develop. Over 4320 species have been identified in about 135 genera. One preferred food is Tipulidae larvae and other groups inhabiting the banks of ponds and streams. Earthworms and snails are also attacked. Tabanus stigma F. is known to develop in drying seaweed in Puerto Rico, the larvae feeding on sand fly larvae. Davis (1919) recorded several species of Tabanus as predaceous on Scarabaeidae grubs. The eggs of most species are laid in large masses on foliage overhanging water or on stones or other nearby objects. With some species they are found in a single compact layer, the eggs placed vertically, side by side; while in others they are several layers deep (Clausen 1940/62)
Brachycera = "short antennae" includes larger flies with large eyes.
Tabanidae. -- <Habits>; <Adults> & <Juveniles> -- The horse flies and deer flies are vicious biters, and they inject toxic saliva into their hosts. The larvae are aquatic and predaceous. The adults may spread diseases such as Tularemia, Loiasis and Anthrax.
Primarily important species are in the genera Tabanus, Haematopota and Chrysops (See Distinctions). Service (2008) noted that they might vector Anthrax, Tularemia, Loa Loa in Africa and even Lyme Disease. They are especially important pests of domestic animals in their ability to transmit bacteria, protozoa viruses and filarial worms. Tabanids are also a problem because of their painful bites, which can result in allergic responses. Images of important species created from collection specimens include: Apatolestes sp., Atylotus sp., Chrysops sp., Diachlorus sp., Esenbeckia sp., Goniops sp., Haematopota sp., Silvius sp., Stenotabanus sp., Stonemyia sp., Tabanus sp.
A critically important disease is Loiasis that can be vectored to humans by tabanids. It is found mostly en the equatorial rainforests of Central Africa. Service (2008) listed Chrysops silaceus and C. dimidiatus as primary vectors, but C. distinctipennis and C. longicornis have some importance in other parts of Africa.
Adult flies feed on sweet substances in the environment, but females also attack mammals and humans. Some also attack birds. Females lay eggs were the larvae are able to survive, such as damp or aquatic sites. The waterproof eggs are glued in a secluded fashion on the bottom of leaves, stones and rocks. Hatching can occur from four days to two weeks depending on temperature and varying with different species. The larvae complete their development in damp sites of standing water, which can last up to two years even in tropical environments. Tabanus and Haematopota species are also predaceous or cannibalistic (Service 2008). Larvae that are carnivorous inject venom into the prey and adults can cause pain when they bite humans. Chrysops larvae are mostly scavengers. Before the onset of pupation the larvae will move to drier habitats adjacent to their larval sites.
Most species females feed during the day in full sunlight, but some are also active only at twilight. Hosts are found by sight and olfactory stimuli. They are all strong fliers, which allow them to fly several miles or kilometers. Their habitats are primarily in and around forested areas. Chrysops species are especially abundant in wooded marshes and swamps, but they can range to open fields. Generally adults remain outdoors although a few African species may enter dwellings. The abundance of adults is influenced by the season in all areas where they occur. In areas with a rainy season the start of rains will trigger activity.
The Tabanidae are extremely difficult to control, especially in areas where aquatic habitats cannot be practically reduced, such as swamps and lakes. Nevertheless, . Control measures have involved draining swampland where the flies breed. Insecticidal control is also plagued by the development of resistance and difficulties in locating principal breeding areas. Service (2008) noted that some control could be achieved with attractant traps for adults and the use of repellents.
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