This document provides information about three insects of medical importance: tsetse flies, simulium flies, and bed bugs. It describes the key characteristics, life cycles, means of pathogen transmission, and control measures for each. Tsetse flies transmit trypanosomes causing human sleeping sickness and animal trypanosomiasis. They are found in Africa and have complex life cycles involving larvae developing in soil. Control involves clearing vegetation from water sources and using traps/insecticides. Simulium flies transmit filarial worms and are found near woodland streams, biting humans and cattle. Their larvae develop in streams and control targets breeding sites. Bed bugs feed solely on blood and belong to the Cimex genus, transmitting no

1. Session 3: Insecta of Medical
Importance: Diptera-Tsetse
Flies, Simulium and Bed Bugs

2. Learning Objectives
By the end of this session, students are expected to
be able to:
• Describe characteristics, life cycles, pathogen
transmission and control measures of Tsetse flies
• Describe characteristics, life cycles, pathogen
transmission and control measures of simulium
• Describe characteristics, life cycles, pathogen
transmission and control measures of bed bugs

3. Tsetse Flies (Glossina)
• Tsetse flies are bloodsucking flies in the genus
Glossina.
• Tsetse flies are diptera which plays a role as
vectors of trypanosomes of man and animals.
• The genus Glossina includes several species which
are vectors of trypanosomes of man and animals.
• Tsetse flies of medical importance belong to two
groups, the palpalis group and morsitans group

4. Palpalis group
• Glossina palpalis
• Glossina tachnoides
• Glossina fuscipes
Morstans group
• Glossina morsitants
• Glossina pallidipes
• Glossina swynnertoni

5. Classification of Tsetse fly
• Tsetse fly are large biting flies that inhabit much
of mid-continental Africa between the Sahara and
the Kalahari deserts.
• They live by feeding on the blood of vertebrate
animals and are the primary biological vectors of
Wuchereria bancrofti, which cause Elephantiasis ,
trypanosomes, which cause human sleeping
sickness and animal trypanosomiasis, also known
as nagana.

6. Cont…
• Tsetse include all the species in the genus
Glossina, which are generally placed in their own
family, Glossinidae belong to kingdom Animalia,
phylum Arthropod, class Insecta, order Diptera .
• Morsitans group: Tsetse species in this group
inhabit the savanna woodlands of Africa.
• The flies are highly mobile and include the more
important vectors of animal trypanasomiasis,
such as Glossina pallidipes, G. morsitans
morsitans, G. longipennis and G. austeni

7. Cont…
• Palpalis group: Species in this group are
mainly found in riverine habitats. They include
important vectors of human sleeping sickness
such as G. fuscipes and G.palpalis spp.
• Fusca group: These are humid forest species.
They are considered to be relatively less
important as vectors than Morsitans and
Palpalis groups since the habitats they occupy
are less used by livestock and people.

8. • Some species such as G. brevipalpis have
nevertheless been found to be significant
vectors of animal trypanosomiasis.
• The tsetse genus is generally split into three
groups of species based on a combination of
distributional, behavioral, molecular and
morphological characteristics.
•

9. Cont…
 The genus includes
• The savannah flies: (Subgenus Morsitans,
occasionally named Glossina): Glossina
austeni, Glossina pallidipes Glossina
swynnertoni
• The forest flies: (Subgenus Fusca, previously
named Austenia): Glossina fusca fusca,
Glossina fuscipleuris, Glossina frezili, Glossina
longipennis

10. Cont
• The riverine flies: (Sub-genus Palpalis,
previously named Nemorhina): Glossina
caliginea Glossina fuscipes fuscipes Glossina
fuscipes martinii Glossina fuscipes quanzensis
Glossina palpalis palpalis Glossina palpalis
gambiensis Glossina tachinoides

11. Morphological Characteristics
• A typical tsetse fly has a yellow to brown body or
black, depending on the species, and is generally
larger than a housefly measuring 6-13 mm
• Resting position of the wings, which fold over
each other like scissors
• Slender, horizontal proboscis with its bulbous
base
• Branched, curved bristles on the arista of the
three-jointed antennae

12. Cont…
• The arista are the prominent bristle on the
largest, distal, segment of the antenna
• Presence of the ‘hatchet’ cell or ‘cleaver cell’
enclosed between 4th and 5th longitudinal
wing veins
• Palps are as long as the proboscis

13. Cont…
• The head has large eyes, distinctly separated
on each side, and a distinct, forward-pointing
proboscis attached underneath by a large
bulb.
• The thorax is large, made of three fused
segments.
• Three pairs of legs are attached to the thorax,
as are two wings and two halteres.

14. Cont
• The abdomen is short but wide and changes
dramatically in volume during feeding.
• Most tsetse flies are physically very tough.
• Are large, narrow bodies and yellow, brown to
greyish or black

15. Cont…
• Measures 6 – 15 mm long, and they are stout
(stronger)
• Having palps as long as proboscis
• Having short antennae with three segments
• Wings are forded scissor like over the back on
resting, “hatchet cell” or “cleaver cell” or “disco
cell” enclosed between the fourth and wing
venation
• Abdomen in some species is striped and spotted

17. Head:
• Having palps as long as proboscis
• Having a pair of compound eyes
• Having short antennae with three segments
• Have a distinct proboscis, a long thin structure
attached to the bottom of the head and
pointing forward

18. Proboscis
• Tsetse has a distinct proboscis, a long thin
structure attached to the bottom of the head
and pointing forward.
Branched arista hairs
• The antennae have arista with hairs, which are
themselves branched.

21. Environmental Occurrence of the
Vector
• The various species occupy a wide range of habitats,
each species having preferred climate, vegetation, and
fauna, but all requiring warmth and moisture
environment
• There are two general classes
o The riverine species, (Palpalis group) e.g. Glossina
palpalis is frequently found in hot
damp areas along the streams, rivers, and lakes in West,
East and Central Africa
o The woodland species (Morsitans group) e.g. Glossina
morsitans, are found in wooded and bush country that
provides moderate shade in East Africa

22. Cont…
• Tsetse flies are found only in Africa
• The fly belts are irregular zones of varying dimensions
surrounded by localities that are practically fly-free
• The life span of the male is about ½ that of the female,
which for female is about 13 weeks
• Both males and females are day time biters of animals and
man
• Vision and smell are the primary factors in directing the flies
to their hosts.
• Glossina palpalis is attracted by black or blue clothing
• The effective flight range is about ½ a km for glossina
morsitans and about 3 km wide for glossina palpalis.

23. Life Cycle
• The breeding grounds for the riverine species are sandy
beaches and loose soil near water.
• The breeding grounds for the bush species are loose soil
near fallen trees or low branching limbs of trees.
• The female produces a single, large, mature, 3rd stage
larva at intervals of about 10 days.
• Glossina palpalis yields a total of nine larvae.
• The larva burrows to a depth of 2 inches in the ground
and immediately pupates.
• The adult fly emerges in about 5 weeks.

24. Medical Importance of Tsetse Flies
• Transmits by injecting trypanosomes to man
and domesticated animals leading to
trypanosomiasis.

25. Control of Tsetse Flies
• Riverine tsetse flies
o Clearing trees and bush from stretches of river
banks
o Selective removal of shrubs and trees along
the stream
o Adult flies can be reduced by trapping and by
selective insecticiding.
o Male sterilization

26. Woodland tsetse
o Clearance of tracts for agricultural purposes
o Selective bush clearance
o Trapping of flies
o Use of insecticides e.g. Dieldrin, BHC, and DDT
to eliminate residual flies
o Sterile male technique
o Spraying of vehicles entering and leaving the
tsetse fly infested areas

27. Trapping by Tsetse trap

28. Simulium Black /Buffalo Fly
Common Names
• Black flies
• Buffalo gnats
Morphological Characteristics
• Black flies are identified by their small size (2-3 mm),
stout hump-backed forms, short legs, conspicuous
compound eyes, short smooth antennae, and venation
of the unspotted wings.
• Proboscis is short and has blade-like cutting organs.
• Body covered with short golden or silver hairs that give
it a longitudinally striped appearance

30. Environmental Occurrence of
Simulium
• Simulium breeds in moderately swift woodland streams
in upland regions.
• They remain near, or move along, these shaded
watercourses.
• Their migratory range is usually 2 to 3 miles, rarely over
8.
• The females bite during the daytime, especially in the
morning and toward evening in open places at the
edge of thick vegetation.
• They may enter darkened houses, and they bite humans
in the vicinity of buildings.
• Fishermen are particularly at high risk.

31. Life Cycle
• Eggs are laid in batches of 300 – 500 and are attached
by a gelatinous secretion to stones, leaves, submerged
plants, stakes, and branches.
• In 3 to 5 days, a yellowish-green, cylindrical larva
emerges and attaches itself in an upright position to
rocks, aquatic vegetation, fresh-water crabs, and other
debris.
• It moults seven times in 13 days to become a pupa.
• The adult emerges in about 3 days.
• Emerging adults live from two to three weeks, to as
long as 85 days.

32. Medical Importance of Simulium
Species
• Simulium transmits Ochocerciasis in man and
cattle
• They bite and lead to bleeding and swelling
o The bite often is painless at first but bleeds
profusely.
o Later swelling, pruritus, and pain develop which
may continue for some days.
o In susceptible individuals even a few bites may
cause marked local inflammation and general
incapacity

33. Control
• Control of black flies is difficult because of the
number of potential breeding sites.
• Mechanical destruction of breeding places is
effective but expensive.
• Fine head nets, tight sleeves, and trousers, and
repellents are used for personal protection.

34. Bed Bugs
• Bed bugs are small wingless insects that feed
solely upon the blood of warm-blooded
animals.
• They belong to the genus Cimex.
• The common species are Cimex lectularius and
Cimex hemipterus

35. classification
•
• Kingdom: Animalia,
• Phylum: Arthropod,
• Class: Insecta,
• Order: Hemiptera
• Family: Cimicidae and Reduviidae
• Genera: Cimex and Triatomid
Species for Cimex bug:
• Cimex lectularis
• Cimex rotundatus
• Cimex hemipterus
Species for Triatoma bug:
• Triatoma infestans
• Panstrongylus megistas
• Rhodnius prolixus.

36. Morphological Characteristics
• Bed bugs are oval, dorsoventrally flattened, brown
coloured insects whose bodies are covered with short,
stout, or serrated hairs
• The female is 5.5mm and is slightly larger than the male
• Its flattened triangular head bears prominent
compound eye, slender antennae and specialized
mouth parts in along proboscis
• The proboscis is flexed backwards beneath the head
and thorax when not in use
• Each of the three thoracic segments bears a pair of legs
that terminate in a pair of simple claws

37. Bedbugs.
• Are reddish brown in colour
• Have oval, dorsoventrally flattened body
• Have prominent compound eyes
• Has slender antennae
• Has long proboscis flexed backward beneath
the head and thorax when not in use

38. Cont..
• Has three pairs of legs that terminate in a pair of
simple claws
• Has short wing pads but cannot fly
• Measures 4 – 6 mm long
• Body covered by simple serrated hairs,
• Female larger than male,
• The mouthparts have labium with a hollow gutter
containing the piercing and sucking apparatus,
the mandible and maxilla

39. bugs

40. Morphological Features of Bed Bug
and Eggs

41. Reduviid bugs (triatomid bugs
• Has elongated or pointed head
• Has prominent compound eyes, usually two ocelli
• Has four-jointed antennae
• Has a three- segmented, ventrally folded slender
proboscis
• The long, rather narrow, flattened body
• Has functional wings with markings

42. Cont…
• Has three pairs of long with 3 jointed legs
• Has dark brown with red, yellow or orange
markings on body
• Measure 1.5-2.0cm,,
• Have long antenna,
• Only adults have wings
• Have markings on thorax.

43. triatomid bugs

44. Life Cycle of Bed Buds
• The female lays about two eggs per day.
• The eggs are white, avoids, and about 1mm in
length.
• Hatching takes place in 4-10 days.
• Development is by incomplete metamorphosis.
• The larva passes through 5-6 nymph stages at
intervals of a week and become sexually mature
adult.
• The life span of the adult is 6-12 months

45. LIFE CYCLE OF BED BUGS:
• Are hemimetabolous;
Eggs larva (nymph) adult

46. Life Cycle of Bed Bug

47. Triatomid bugs:
• The female lays white or yellowish-pink, smooth,
barrel-shaped eggs, in batches of 8 to 12, which
hatch in 10 to 30 days.
• Development is by incomplete metamorphosis.
• The young bug must obtain its first blood meal
within days, and undergoes a lengthy
metamorphosis during six to more than 12
months to the adult stage, with blood meals
between each molt.
• Adults are long lived and can survive for several
weeks without a blood meal.

48. Medical Importance of Bed Bugs
• Bed bugs are not known to transmit any
pathogen but their bites are painful and
produce itching wheals.
• Some people, especially children develop
urticaria, allergic reactions example asthma.
• However, it is reported to be capable of
transmitting pathogens mechanically.
• They are nuisance insects.

49. Explain the disease transmitted by
Bugs
• Bites of both bugs produce lesions that are range from
small red marks to haemorrhagic bundle
• Romana’s sign (the classic periorbital oedema secondary to
a triatomid bite)
• Vector of American trypanosomiasis that caused by T. cruzi
(Sleeplessness in adult and children)
• Their bites are irritating and become red itching wheals and
bullae.
• Transmit hepatitis B.
• It may act as a mechanical carrier, but it is not a proved
biological vector of human diseases.

50. Control of Bed Bugs
• Bedbug may be controlled by
o Plastering cracks and crevices of houses.
o Application of insecticides, example DDT,
Lindane, or Malathion.
• These insecticides can be applied to floors,
walls, furniture and mattresses

51. Key Points
• The genus glossina includes several species which
are vectors of trypanosomes of man and animals.
• Tsetses flies of medical importance belong to two
groups namely palpalis group and Morsitans
group.
• Simulium transmits Ochocerciasis in man and
cattle. They bite and lead to bleeding and
swelling.
• Bed bugs are small wingless insects that feed
solely upon the blood of warm-blooded animals.

52. Cont…
• The common species of bed bugs are Cimex
lectularius and Cimex hemipterus.
• Bed bugs are not known to transmit any
pathogen but their bites are painful and
produce itching wheals.
• Control measures of Tsetse-flies, Simulium and
Bed bugs are based on environmental factor
and use of insecticides

53. Evaluation
• What is the medical importance of tsetse-
flies?
• What are the factors which favour occurrence
of the simulium species?
• What are the control measures of bed bugs?

54. References
• CDC (2009). Parasites and Health: Bed Bugs. Retrieved on
4th May 2005 from
http://www.dpd.cdc.gov/dpdx/HTML/Bedbugs.htm.
• Cook, G. (2000). Manson’s Tropical Diseases (22nd ed.).
London: WB Saunders Company Ltd.
• Hagner, R. Root, M. Augustine, L.et al. (1939). Parasitology,
with Special Reference to Man and Domestic Animals. New
York Inc.: D. Appleton-Century Company.
• Harwood, R.F. & James, M.T. (1979). Entomology in Human
and Animal Health (7th ed.). Pulman: Washington State
University.
• Mike, S. (2004). Medical Entomology for students. London:
Oxford University Press.

55. Cont…
• Monica, C. (1998). District Laboratory Practice in Tropical
Countries. Part 1. Tropical Health Technology. NOIDA, India:
Gapson Papers Ltd.
• Monica, C. (2000). District Laboratory Practice in Tropical
Countries. Part 2. Tropical Health Technology.UK:
Cambridge University Press.
• Service, M.W. (1986). Lecture Notes on Medical Entomology
for students. London: Blackwell Scientific Publications.
• United Republic of Tanzania. (2007). Training Course on
Laboratory Diagnosis of Malaria: Malaria Control Series 17.
National Malaria Control Programme of the Ministry of
Health and Social Welfare.