Tsetse files – the transmitters of the sleeping sickness parasites
Tsetse flies are found only in Africa and throughout the continent there are 31 species and sub-species which can be divided into three main groups.
The Mortisans group is mainly found in savannah woodland and
includes the species Glossina mortisans, G. pallipides andG.
austeni. The Palpalis group is mainly found in the riverine
woodlands of western and central Africa and includes vectors
(transmitters) of human sleeping sickness such as G. fuscipes and
G. palpalis. The Fusca group is mainly found in humid forests and
one species, G. brevipalpis, is a vector of nagana.
Tsetse reproduction is different from most other insects. Female
tsetse flies only mate once. Seven to nine days later a single egg
develops into a larva within the uterus. About nine days later the
larva is born and it burrows into the ground and pupates. The adult
fly emerges from the pupa after about 30 days. This contrasts with
most other flies and insects which usually lay hundreds or
thousands of eggs. Their slow rate of reproduction means that
tsetse populations can be eradicated by killing just 2-3 % of the
female population per day and it also means that tsetse rarely if
ever become resistant to insecticides.
Tsetse feed exclusively on blood and the different species of
tsetse seem to prefer feeding on the blood of different types of
animals. For instance, Glossina morsitans often feed on wild pigs,
such as warthog and bush-pig, and buffalo. Glossina fuscipes,
however, prefer to feed on monitor lizards. Where humans and their
livestock are present, many natural hosts disappear but domestic
livestock such as cattle and pigs - and people themselves- act as
ideal substitutes for these wild hosts.