Glossinidae Tsetse Flies 161 Systematics

There are about 30 species of tsetse fly belonging to the genus Glossina (Diptera, Brachycera) subdivided into three subgenera: Austenina (or G. fusca group), Nemorhina (or G. palpalis group) and Glossina (or G. morsitans group), of which the latter two are of medical importance. The Nemorhina subgenus includes tsetse fly species found in forest galleries, vegetation close to rivers, lakes, and mangroves of Western and Central Africa. The main vectors are G. palpalis palpalis, G. p. gambiensis, G. tachinoides and G. fuscipes quanzensis. The Glossina subgenus includes xerophilous or savanna species occurring in Central, West and East Africa, associated to woodlands, deforested savannas, but seldom associated to cultivated lands.

Tsetse flies are confined to tropical Africa (at a latitude of 15° N to 20° S), but absent from Madagascar. Some species have a broad distribution like Glossina morsitans present in Eastern, Central and West Africa, whereas G. palpalis is found only in West Africa. Tsetse flies are vectors of human (sleeping sickness) and animal trypanosomiasis. The most important species as vectors are G. palpalis, G. tachinoides, G. fuscipes, G. pallidipes, G. swynnertoni and G. morsitans.

1.6.2 Morphology

The first and second instar larvae are found directly in the uterus of the female. The female lays a third-instar larva which measures 1 cm, with the shape of a maggot. This free-living third-instar larva has a brief existence. The pupa is protected by a dark and hard ''shell''. The adult tsetse flies have a long piercing proboscis and their wings are closed over the abdomen as scissors (see Figure 1.11). The length of the adults ranges from 8 to 15 mm.

1.6.3 Biology

The immature development of the tsetse fly is peculiar as only one egg develops at a time. The first instar larva hatches in utero after three to four days, the second and third instar larvae follow one another in eight to twelve days. The larva stage 3 (8-9 mm in length) is deposited by the female; this reproduction is referred to as ''adenotrophic viviparity''.1 A female will lay six to ten larvae during its lifetime. The first larva is deposited approximately 16-20 days after adult emergence. The larva is deposited on the ground in shaded places and in soft soil where it hides, and 15 minutes later it becomes a pupa. This stage lasts about 30 days according to the species, sex and ecological conditions. The imago emerges from the pupa and it will take its first blood meal one to two days after the adult

Figure 1.11 Adult tsetse-fly (Photo © IRD, Michel Dukhan).

emergence. Both females and males are hematophagous and bite men, domestic and wild mammals, as well as reptiles and birds. Tsetse flies do not limit themselves to a single host, but the majority of species have food preferences. Glossina palpalis bites human and reptiles, G. tachinoides bites human and cattle, and G. longipennis bites the elephants, rhinoceroses and hippopotamuses. They take a blood meal every two to four days (shorter periods during the dry season and longer periods during the rainy season extending to 10 days). They bite during the daytime. Mating takes place only once. The adult lifespan is about two to three months (up to five to six months). Tsetse flies are capable of flying at 25 kilometres per hour but they cannot sustain flights for more than a few minutes. The vision of tsetse flies is important as they are attracted by dark colours and this is used to catch them with black and blue traps.

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