Previous Page Table of Contents Next Page


CHAPTER 5
DISTRIBUTION OF GLOSSINA

5.1 GENERAL NOTES

The field officer will normally use a map of the tsetse distribution in his own country: the National Map of Tsetse Distribution. This nap will be revised from time to tine by national headquarters.

The field officer will in the course of his work make observations on the changes in fly distribution in his area, and notify his head office accordingly.

There are good reasons why the field officer should take an interest in tsetse distribution in areas wider than just his own country (Map 5.9).

  1. Very often, tsetse belts continue from one country to the next, across the national boundary. Large scale tsetse operations have to take this into account, and often there will have to be liaison between field officers in adjacent areas that are separated by international bound aries. This kind of cooperation is likely to be more important in the future than it has been in the past.

  2. Sometimes, an expansion of a tsetse belt in one country may cause the belt to come up to and cross an international boundary. Tsetse control personnel should therefore be aware of the situation in adjacent countries, and to be prepared for these possible developments.

  3. Knowing the continental distribution of tsetse species gives the field officer a greater understanding of what stops the fly from spreading further, and whether a spread beyond the present limits in a particular country is likely.

5.2 DISTRIBUTION OF MORSITANS GROUP SPECIES (Map 5.10estern shows location of countries)

Morsitans group species do not live in the wettest areas (rain forest, mangrove swamp, see Volume II, Chapter 1), but are present throughout much of the savannah (grassy woodland) of Africa. Their distribution appears to be limited by cold winter conditions in the south (Zimbabwe, Botswana), and hot dry conditions in the north of West and Central Africa. Where climatic conditions are less severe, their distribution may be limited by scarcity of game animals on which to feed and by lack of trees.

Glossina morsitans (Map 5.1) is the most widespread species. Its distribution is not accurately known in all countries. The subspecies G.m. submorsitans extends as a very large but broken belt throughout West Africa, into southern Sudan, northern Uganda.and Ethiopia. Very large belts of G.m. centralis occur in Zaire, Zambia, Angola, Botswana, Tanzania, Rwanda and Burundi; belts of G.m. morsitans occur in Tanzania, Mozambique, Zimbabwe, Zambia and Malawi.

The boundary separating the two subspecies G.m. centralis and G.m. morsitans corresponds roughly with the Atlantic/Indian Ocean watershed.

Glossina swynnertoni (Map 5.1) is limited to belts in Kenya and Tanzania between Lake Victoria and the Indian Ocean.

Glossina pallidipes (Map 5.2) extends along the Kenya and Somalia coastal regions and is abundant in Somalia along certain river valleys. It is also present in Ethiopia, Sudan, Tanzania, Mozambique, Zimbabwe, Zambia, Zaire and Uganda.

Glossina longipalpis (Map 5.2) is present as a broad belt in West Africa from Senegal to Nigeria, with isolated belts on the Nigerian/Cameroon border and in northwestern Zaire (Equateur). In general, it occurs in areas more to the south than the G. morsitans belts in most savannah areas, although there is some overlap between the two species.

Map 5.1

Map 5.1 Distribution of Glossina morsitans (in black) and the closely related G. swynnertoni(stippled)

Map 5.2

Map 5.2 Distribution of Glossina longipalpis (west of the drawn line) and G. pallidipes(east of the line).

Map 5.3

Map 5.3 Distribution of Glossina austeni.

Glossina austeni (Map 5.3) occurs only in the east coast countries of Somalia, Kenya, Tanzania, Mozambique and northeastern parts of South Africa. It has also been recorded from Zimbabwe.

5.3 DISTRIBUTION OF PALPALIS GROUP SPECIES IN AFRICA

The palpalis group is mainly limited to the very humid areas of Africa, the mangrove swamps, the rain forest, the lake shores and the gallery forests along rivers.

Members of this group, when they penetrate generally drier areas, do not move far away from free water (rivers and lakes): but in generally more humid areas they may not have to live so close to free water.

Glossina palpalis (Map 5.4) lives in the more humid areas of West Africa, from Senegal to Cameroon, then south along the coast to Angola. In West Africa it penetrates further to the north in Mali and Senegal, than it does in Nigeria. In the part of its distribution from Cameroon to Angola, it has a long common boundary with G. fuscipes, with which there is little overlap.

Glossina fuscipes (Map 5.4) occupies a very large inland block of Africa centred on Zaire, but covering some of the land in all of the countries surrounding Zaire, as well as Gabon, Cameroon and the southern part of Chad.

Glossina tachinoides (Map 5.5) is distributed in a broad belt from Guinea in the west, to the Central African Republic to the east. In addition, much further to the east are some smaller isolated belts on the Sudan-Ethiopian border. In Nigeria and Chad this species is able to live further north than either G. palpalis or G. fuscipes.

Glossina caliginea and G. pallicera are mainly limited to mangrove and thick forest areas of West Africa, as far east as Gabon.

Map 5.4

Map 5.4 Distribution of Glossina palpalis and G. fuscipes. The approximate boundary between the two species is shown as a dashed white line. There is a small amount of overlap between the two species.

Map 5.5

Map 5.5 Distribution of Glossina tachinoides

5.4 DISTRIBUTION OF FUSCA GROUP SPECIES IN AFRICA

The distribution patterns of the fusca group species are of three main types.

  1. Distribution of Glossina longipennis(Map 5.6)

    This species is confined to Sudan (south east comer), Ethiopia (southern border), Somalia, Kenya, and Tanzania (north eastern quarter). It inhabits generally rather dry country.

  2. Distribution of Glossina brevipalpis(Map 5.7)

    This species is widely scattered throughout eastern parts of Africa, from Ethiopia and Somalia in the north, to Mozambique and South Africa in the south. There is a large belt west of Lake Tanganyika, in Zaire.

  3. Distribution of the remaining fusca group species (Map 5.8).

    Taken together, the remainder of the fuscagroup species are limited to the more thickly forested areas of Africa, and so have a pattern of distribution rather like that of G. palpalis/G. fuscipes(Map 5.4), with the difference that because fusca group flies do not usually penetrate very far up gallery forests, their distribution is more limited than that pair. Some species such as G. tabaniformis, G. nashi and G. haningtoni are more restricted to rain forests than other species such as G. fusca, G. medicorum, G. fuscipleuris and G. schwetzi,which are forest edge species. Glossina medicorummay live in riverine habitats in Upper Volta and Ivory Coast.

Map 5.6

Map 5.6 Distribution of Glossina longipennis

Map 5.7

Map 5.7 Distribution of Glossina brevipalpis

Map 5.8

Map 5.8 Distribution of fusca group species (excluding G. brevipalpis and G. longipennis)

5.5 GLOSSINA SPECIES/COUNTRY TABLE

CountryPalpalis GroupMorsitans GroupFusca Group
    
Angolapalpalis
fuscipes
pallicera
morsitanstabaniformis
schwetzi
nashi
haningtoni
Beninpalpalis
tachinoides
morsitans
longipalpis
fusca
medicorum
Botswana morsitans 
Burundifuscipesmorsitans
pallidipes
brevipalpis
Cameroonpalpalis
fuscipes
tachinoides 
pallicera
caliginea
morsitans
longipalpis
fusca
nigrofusca
tabaniformis
haningtoni
nashi
Central
African
Republic
palpalis
fuscipes
tachinoides
pallicera
caliginea
morsitansfusca
fuscipleuris
tabaniformis
nigrofusca
haningtoni
nashi
medicorum
Chadfuscipes
tachinoides
morsitans 
Congo, P.R.palpalis
fuscipes
pallicera
 fusca
tabaniformis
schwetzi
haningtoni
nashi
Equatorial Guineapalpalis
fuscipes
 fusca
tabaniformis
haningtoni
Ethiopiafuscipes
tachinoides
morsitans
pallidipes
longipennis
brevipalpis
Gabonpalpalis
fuscipes
pallicera
caliginea
 fusca
tabaniformis
schwetzi
medicorum
haningtoni
nashi
Gambiapalpalismorsitans
longipalpis
 
Ghanapalpalis
tachinoides
pallicera
caliginea
morsitans
longipalpis
fusca
medicorum
nigrofusca
tabaniformis
Guineapalpalis
tachinoides
pallicera
morsitans
longipalpis
fusca
tabaniformis
nigrofusca
Guinea
Bissau
palpalismorsitans
longipalpis
fusca
Ivory Coastpalpalis
tachinoides
pallicera
morsitans
longipalpis
fusca
medicorum
nigrofusca
tabaniformis
Kenyafuscipesmorsitans
swynnertoni
pallidipes
austeni
longipennis
brevipalpis
fuscipleuris
Liberiapalpalis
pallicera
 fusca
medicorum
nigrofusca
Malawi morsitans
pallidipes
brevipalpis
Malipalpalis
tachinoides
morsitans 
Mozambique morsitans
pallidipes
austeni
brevipalpis
Namibia morsitans 
Nigertachinoidesmorsitans 
Nigeriapalpalis
tachinoides
pallicera
caliginea
morsitans
longipalpis
fusca
medicorum
tabaniformis
nigrofusca
haningtoni
Rwandafuscipesmorsitans
pallidipes
brevipalpis
Senegalpalpalismorsitans
longipalpis
 
Sierra
Leone
palpalis
pallicera
longipalpis
morsitans
fusca
nigrofusca
Somalia pallidipes
austeni
longipennis
brevipalpis
South Africa austenibrevipalpis
Sudanfuscipes
tachinoides
morsitans
pallidipes
longipennis
fusca
fuscipleuris
Swaziland austeni 
Tanzaniafuscipesmorsitans
swynnertoni
pallidipes
austeni
longipennis
brevipalpis
fuscipleuris
Togopalpalis
tachinoides
morsitans
longipalpis
fusca
Ugandafuscipesmorsitans
pallidipes
longipennis
brevipalpis
fusca
fuscipleuris
tabaniformis
nigrofusca
Upper Voltapalpalis
tachnioides
morsitans
longipalpis
medicorum
Zairepalpalis
fuscipes
pallicera
morsitans
longipalpis
pallidipes
fusca
fuscipleuris
tabaniformis
nigrofusca
haningtoni
schwetzi
severini
vanhoofi
brevipalpis
medicorum
Zambiafuscipesmorsitans
pallidipes
brevipalpis
Zimbabwe morsitans
pallidipes
austeni
 

5.6 FACTORS LIMITING DISTRIBUTION

The pattern of distribution of tsetse species is a result mainly of climatic and ecological barriers preventing further spread.

For example, Glossina austeni could probably live in much of West Africa, but it has never had the chance to invade those areas, because of the high ground, unsuitable habitats and great distances between these parts.

Specimens of the palpalis group have never reached river systems draining into the Indian Ocean. Had they done so, probably much of the east coast would have been infested by some of these species.

There follows a brief description of the way in which some climatic and vegetational features, as well as the availability of food, may limit the broad distribution of tsetse flies in the continent of Africa. A description of the ways in which these factors affect the lives of tsetse flies, including local distribution, may be found in Volume II, 1.1. (see also Map 5.9)

5.6.1 Low temperatures Long periods of low temperatures occur at the southern end of the distribution of the tsetse fly, in southern Mozambique, Zimbabwe, Botswana, southern Angola and southern Zambia. The long cold winters in these countries, often with frost, make conditions that are not suitable for tsetse. In cold weather the fly cannot move about to feed. In cold soil, the pupa cannot complete its development before its stored food supplies are finished.

High ground further north also has a climate too cold for the tsetse fly to live, for instance in the highlands of Kenya and Ethiopia, and along the watersheds between river basins.

Map 5.9

Map 5.9 Distribution of Glossina, compared with the distribution of wet forest, moist savanna and dry savanna regions of Africa.

5.6.2 High temperatures Very high temperatures combined with dryness and lack of cover make conditions in the north of West Africa, in most parts of the Sudan, and parts of Kenya, Ethiopia and Somalia unsuitable for tsetse. Where the general climate is too hot, tsetse flies may make use of local cooler areas, for example along rivers having gallery forest, in which to live.

5.6.3 Dry conditions Pupae of many species of tsetse require a humid (but not damp) soil in which to live. This probably helps to limit the distribution of most species with the exception of some morsitans group species and G. longipennis.

The habit of living in gallery forest close to water makes it possible for palpal is group species, especially Glossina palpalis and G. tachinoides, to have a more northerly spread in much of West Africa than morsitans group species.

5.6.4 Lack of food Insufficient food may cause some areas to be without tsetse, even though the areas may be suitable in other respects. The Kalahari sands woodland of Zambia (Western Province), Zimbabwe and Bots wana may be an example.

The rinderpest outbreak that swept through Africa at the end of the last century destroyed most of the animals fed upon by tsetse and the fly belts were greatly reduced. Both the game populations and the tsetse belts have recovered since that time, or are still in the process of recovering at the present time.

5.6.5 Lack of vegetation cover Vegetation such as trees, bushes or thickets are required by tsetse as cover from the worst effects of a hot climate. Pure grassland or very low vegetation is almost never used by tsetses as their permanent hone, although patches of grassland may be visited and crossed by than.

Some species may prefer a particular type of vegetation. For example, the patchy distribution of Glossina ansteni is in part due to the patchy distribution of the humid evergreen thickets in which it lives.

5.6.6 Combination of these factors Very often certain of these factors work together and limit the distribution of tsetse. For example, in the north of West Africa, away from the rivers the climate may be seasonally very hot, the vegetation low and grassy and the conditions very dry. It is only near to rivers that some bushes and trees can grow, giving shade and cooler conditions and trapping some moisture, allowing flies to survive.

In some of the miombo woodland of East and Central Africa, tsetse may be absent, rare or common, according to mean temperatures and abundance of game. In areas in which the mean temperature may be thought to be too low, tsetse may yet be present because of the local abundance of game.

Map 5.10

Map 5.10 Map to show the boundaries and names of those African countries that have tsetse infestations.


Previous Page Top of Page Next Page