2. Introduction
There are 31 species and subspecies of tsetse flies,
but the actual number depends on how many forms are
recognized as subspecies.
All tsetse flies belong to the genus Glossina, the only
genus in the family Glossinidae
Tsetse flies are restricted to sub-Saharan Africa from
approximately latitude 10° north to 20° south, but
extending to 30° south along the eastern coastal area.
3. Some species, such as Glossina morsitans, are found
across West Africa to Central and East Africa, whereas
others are more restricted in their distribution.
For example, G. palpalis occurs only in the West African
sub region.
Tsetse flies are vectors of both human and animal
African trypanosomiasis,
The disease in humans being called sleeping sickness.
The most important vectors are G. palpalis, G.
tachinoides, G. fuscipes, G. pallidipes and G. morsitans
4. Morphology
Adults
are yellowish or brown-black robust flies that are rather
larger (6–14mm) than house flies
abdominal segments uniformly coloured
Tsetse flies are distinguished from other flies by the
combination of
(1) a rigid forward projecting proboscis and
(2) a closed cell between wing veins 4 and 5
5.
6. At rest tsetse flies also differ from most flies in
having the wings placed over the abdomen like the
closed blades of a pair of scissors
7. The proboscis is long, with a bulbous base, and points
forwards from the head
When a tsetse fly feeds, saliva containing
anticoagulants is pumped down into the wound formed
by the fly.
Along pair of palps occur dorsally, very close to the
proboscis, and lie alongside it.
Dorsally the thorax has dark brown stripes or patches.
There are eight abdominal segments, which may be
uniformly dark brown or blackish
Both sexes take blood-meals and can be disease
vectors it is not important to distinguish them
8. Life cycle
Both male and female tsetse flies bite people, a large
variety of domesticated and wild mammals, and
sometimes reptiles and birds.
East Africa Glossina swynnertoni feeds mainly on wild
pigs and G. morsitans on wild and domesticated bovids
as well as on wild pigs
G. pallidipes feeds principally on wild bovids
West Africa G. morsitans feeds mainly on warthogs
(Phacochoerus africanus)
G. palpalis feeds predominantly on reptiles and humans,
9. G. tachinoides feeds on humans and bovids, but in
southern Nigeria it feeds predominantly on domestic
pigs.
Tsetse flies blood-feed about every 2–3 days,
although in cool humid conditions it may be about
every 10 days.
Feeding is restricted to the daytime, and vision, as
well as olfactory cues emanating from host breath
and urine, is important in host location,
Dark moving objects being particularly attractive
10. During feeding blood sucked up the proboscis passes to
the crop and later to the mid-gut, where digestion
proceeds.
The different types of flies lay eggs; in marked contrast
tsetse flies do not, but instead they deposit larvae, one
at a time (i.e. they are larviparous).
After females have mated and taken a blood-meal a
single egg in one of the two ovaries completes
maturation.
It then passes down the common oviduct into the
uterus, where it is fertilized by sperm from the paired
11. The egg hatches within the uterus after about 3–4
days.
The uterus is supplied with a conspicuous pair of
branched secretory glands called milk glands
Secretions from these glands provide the larva with all
the food it needs for growth and development.
The larva passes through three instars in the female.
12. Adult behaviour
Knowledge of the behaviour of tsetse flies is essential
for understanding their role in the transmission of
sleeping sickness
For the development of effective control strategies.
Blood-engorged tsetse flies, and unfed hungry flies
waiting to feed, spend the night and much of the day
resting in dark and usually humid sites.
13. In fact tsetse flies spend about 23 hours a day resting
on vegetation.
During the day favored resting sites of most species
are branches and trunks of trees and bushes.
Are not found resting in sites having temperatures
above about 36 °C.
At night tsetse flies rest mainly on the upper surfaces
of leaves.
Accurate knowledge of resting sites may be required
for control measures.
14. Based on their morphology, ecology, karyotype and
behaviour, tsetse flies can be separated into the
following three main groups
1. Fusca group (forest flies)
2. Morsitans group (savanna flies)
3. Palpalis group (riverine and forest flies)
15. Medical importance
All Glossina species are potential vectors of African
trypanosomiasis to humans.
However, relatively few species of tsetse flies are
natural vectors because many species rarely, if ever,
feed on people.
It is the behaviour of adult tsetse flies and the degree of
fly–human contact, and in the case of Rhodesian
sleeping sickness also the degree of vector contact with
reservoir hosts of the trypanosomes, that establishes
whether a tsetse fly is a vector
16. There are two subspecies of trypanosomes causing
sleeping sickness in humans, namely Trypanosoma
brucei gambiense and T. brucei rhodesiense.
Trypanosoma b. gambiensis accounts for 95% of
reported cases of sleeping sickness.
These parasites are morphologically indistinguishable
but produce different clinical symptoms and have
different epidemiologies.
The most important vectors of sleeping sickness are G.
palpalis, G. fuscipes, G. tachinoides, G. morsitans and
G. pallidipes.
17. Vectors of trypanosomiasis (animal & human)
Nagana in animals
Sleeping sickness in man
T. gambiense (Glossina palpalis)
T. rhodesiense(Glossina morsitans)
18. Control
Change the nature of the breeding places so as to
become unsuitable for the fly
Manual collection of pupae
Application of insecticides
Targets and traps
Genetic control (sterile male release)
