The tsetse fly is a large insect that inhabits much of tropical Africa. The parasite consumes the blood of vertebrates. The genus has been extensively studied for its role in the transmission of a dangerous disease. These insects have a significant economic impact in African countries as biological vectors of trypanosomes that cause sleeping sickness in humans and trypanosomiasis in animals.
Origin of the species and description
The word tsetse means “fly” in the Tswana and Bantu languages of southern Africa. It is believed to be a very old species of insect, as fossil tsetse flies have been found in fossil beds in Colorado dating back to about 34 million years ago. Some species have been described in Arabia.
Tsetse flies living today are almost exclusively found on the African continent south of the Sahara. 23 species and 8 subspecies of the insect have been identified, however only 6 of them are recognized as carriers of sleeping sickness and are accused of transmitting two pathogenic human parasites.
Video: Tsetse fly
Tsetse was absent from much of southern and eastern Africa until colonial times. But after a plague pandemic that struck almost all the cattle in these parts of Africa, and as a result of famine, most of the human population was destroyed.
Thorny bush, an ideal landscape for tsetse flies. It grew up where there were pastures for domestic animals and was inhabited by wild mammals. Tsetse and sleeping sickness soon colonized the entire region, effectively precluding the restoration of agriculture and animal husbandry.
Interesting fact! Because agriculture cannot function effectively without the benefit of livestock, tsetse has become the root cause of poverty in Africa.
Perhaps without tsetse, Africa today would have looked very different. Sleeping sickness has been called “Africa's best wildlife keeper” by some conservationists. They believed that a land empty of people, full of wild animals, has always been like that. Julian Huxley called the plains of East Africa “the surviving sector of the rich natural world as it was before the advent of modern man.”
Appearance and Features
All types of tsetse flies can be distinguished by common features. Like other insects, they have an adult body consisting of three clearly distinguishable parts: head + thorax + abdomen. The head has large eyes, distinctly divided on each side, and a clearly visible proboscis directed forward, attached from below.
The thorax is large, consists of three fused segments. Attached to the thorax are three pairs of legs, as well as two wings. The abdomen is short, but wide and changes dramatically in volume during feeding. The total length is 8-14 mm. The internal anatomy is fairly typical of insects.
Four significant features have been identified that distinguish the adult tsetse fly from other fly species:
- Proboscis. The insect has a distinct trunk, with a long and thin structure, attached to the underside of the head and pointing forward;
- Folded wings. At rest, the fly folds its wings completely over each other like scissors;
- The outline of an ax on the wings. The middle cell of the wing has a characteristic ax shape, reminiscent of a meat mallet or an axe;
- Twisted hairs — “antennas”. The awn has hairs branching at the end.
The most characteristic difference from European flies is tightly folded wings and a sharp proboscis protruding from the head. Tsetse flies are rather dull looking, varying in color from yellowish to dark brown, and have a gray chest that often has dark markings.
Where does the tsetse fly live?
Glossina distributed over most of sub-Saharan Africa (about 107 km2). Her favorite places are areas with dense vegetation located along the banks of rivers, lakes in arid areas, and dense, humid, tropical forest.
The current Africa seen in wildlife documentaries was shaped in the 19th century by a combination of plague and tsetse. In 1887 rinderpest virus was inadvertently imported by the Italians.
It spread rapidly, reaching:
- Ethiopia by 1888;
- The Atlantic coast by 1892;
- South Africa by 1897
A plague from Central Asia killed over 90% of the livestock of pastoral peoples such as the Maasai in East Africa. Pastoralists were left without animals and sources of income, and farmers were deprived of animals for plowing and irrigation. The pandemic coincided with a period of drought that provoked widespread famine. The population of Africa died from smallpox, cholera, typhoid and diseases brought from Europe. It is estimated that two-thirds of the Maasai died in 1891.
The land was freed from cattle and people. The reduction of pastures has led to the growth of shrubs. A few years later, the short cut grass was replaced by forest meadows and thorny bushes, an ideal environment for tsetse flies. Populations of wild mammals increased rapidly, and with them the number of tsetse flies increased. The mountainous regions of East Africa, where previously there was no dangerous pest, were inhabited by it, which was accompanied by sleeping sickness, until then unknown in the area. Millions of people died from sleeping sickness in the early 20th century.
Important! The continued presence and expansion of the tsetse into new agricultural areas is hindering the establishment of a sustainable and profitable livestock system in nearly 2/3 of African countries.
Suitable vegetation cover is important for the development of the fly, as it provides breeding grounds, shelter in adverse climatic conditions, and places for its rest.
What does the tsetse fly eat?
The insect is found in wooded areas, although it may fly a short distance into open grasslands when they are attracted by a warm-blooded animal. Both sexes suckle blood almost daily, but daily activity varies by species and environmental factors (such as temperature).
Some species are especially active in the morning, while others are more active in the afternoon. In general, tsetse activity decreases shortly after sunset. In the forest environment, tsetse flies are the cause of most attacks on humans. Females usually feed on larger animals. With a thin proboscis, they pierce the skin, inject saliva and saturate.
Arthropod Diptera Glossinidae Tsetse
It lurks in the bushes and starts chasing a moving target, reacting to the rising dust. It can be a large animal, or a car. Therefore, in areas where the tsetse fly is ubiquitous, it is not recommended to drive in car bodies or with open windows.
It bites mainly artiodactyl animals (antelopes, buffaloes). Also crocodiles, birds, monitor lizards, hares and humans. Her belly is large enough to withstand the increase in size during the absorption of blood, since she takes in blood fluid equal to her own weight.
Tsetse flies are taxonomically and ecologically classified into three groups:
- Fusca or forest group (subgenus Austenina);
- Morsitans or savannah group (genus Glossina);
- Palpalis, or river group (subgenus Nemorhina).
Medicinally important species and subspecies belong to the river and savanna group. The two most significant vectors of sleeping sickness are Glossina palpalis, which occurs mainly in dense coastal vegetation, and G. morsitans, which feeds in more open forest areas.
G. palpalis is the main host of the Trypanosoma gambiense parasite, which causes sleeping sickness throughout West and Central Africa. G. morsitans is the main carrier of T. brucei rhodesiense, which causes sleeping sickness in the highlands of East Africa. G. morsitans also carries trypanosomes that cause infection.
Character and lifestyle features
Tsetse fly aptly called the “silent killer”, because. it flies swiftly, but silently. It serves as a reservoir for numerous microorganisms. Adult males of the species can live from two to three weeks, and females from one to four months.
Curious fact! Most tsetse flies are very tough. They are easily killed with a fly swatter, but it takes a lot of effort to crush them.
From the Sahara to the Kalahari, the tsetse fly has plagued African farmers for centuries. Back in ancient times, this tiny insect prevented farmers from using pets to cultivate the land, limiting production, yields and income. The economic impact of the tsetse fly on Africa is estimated at $4.5 billion.
Transmission of trypanosomiasis involves four interacting organisms: host, vector insect, pathogenic parasite, and reservoir. Glossins are efficient vectors and are responsible for binding these organisms, and any reduction in their numbers should lead to a significant reduction in transmission and therefore contribute to the elimination of HAT and the sustainability of control efforts.
When bitten by a tsetse fly, the transmitted parasites (trypanosomes) cause sleeping sickness in humans and Nagana (African animal trypanosomiasis) in animals — mostly cows, horses, donkeys and pigs. Parasites cause confusion, sensory disturbances, and poor coordination in humans, as well as fever, weakness, and anemia in animals. Both can be fatal if left untreated.
The first continental study of the spread of the tsetse fly was carried out in the 1970s. More recently, maps have been produced for FAO showing predicted areas suitable for tsetse flies.
Social structure and reproduction
Tsetse – produces 8-10 broods in a lifetime. The female tsetse mates only once. Through 7 — For 9 days, she produces one fertilized egg, which she stores in her uterus. The larva develops and grows using maternal nutrients before being released into the environment.
The female requires up to three blood doses for intrauterine development of the larva. Any failure to obtain bloody food can lead to an abortion. After about nine days, the female produces a larva, which immediately burrows into the ground, where it pupates. The hatched larva develops a tough outer layer — puparium. And the female continues to produce one larva at about nine-day intervals throughout her life.
The pupal stage lasts about 3 weeks. Outwardly, the molting skin (exuvium) of the chrysalis — looks like a small, hard shell, oblong with two characteristic small dark petals at the tail (breathing) end of a living substance. The length of the pupa is less than 1.0 cm. In the shell of the pupa, the fly completes the last two stages. An adult fly emerges from a chrysalis in the ground after about 30 days.
Within 12-14 days, the newborn fly matures, then mates and, if it is a female, lays its first larva. Thus, 50 days pass between the appearance of one female and the subsequent appearance of her first offspring.
Important! This life cycle of low reproduction and significant parental effort is a relatively unusual example for such an insect.
Adults — they are relatively large flies, 0.5-1.5 cm long, with a recognizable shape that makes them easily distinguishable from other flies.
Tsetse's natural enemies
Tsetse has no enemies in its natural habitat. Some small birds may catch them for food, but not systematically. The main enemy of the fly is a person who fiercely seeks to destroy it for obvious reasons. The insect is involved in the natural transmission chain of African pathogenic trypanosomes, which are the causative agent of sleeping sickness in humans and domestic animals.
At birth, the tsetse fly is not infected with the virus. Infection with harmful parasites occurs after an individual drinks blood from an infected wild animal. For more than 80 years, various methods have been developed and applied to combat the most dangerous insect on Earth. Many of the advances in baiting techniques have come from a better understanding of fly behavior.
The importance of visual factors in attracting tsetse to bright objects has long been appreciated. However, it took much longer to realize the true importance of the sense of smell in attraction techniques. Artificial tsetse baits work by mimicking some of the body's natural features, with cattle being used as the “ideal” model for testing.
Note! In regions where baits are used to protect the local population or their animals from tsetse attack, traps should be placed around villages and plantations to be effective.
The most effective way to get rid of tsetse is to spay males. It consists in directed radioactive radiation. After sterilization, males who have lost their reproductive functions are released to places where the largest population of healthy females is concentrated. After mating, further reproduction is impossible.
This honey is most effective in areas isolated by water. In other regions, it also bears fruit, but only temporarily reduces the reproduction of insects.
Population and species status
The tsetse fly lives on almost 10,000,000 km2, mainly in tropical rainforests, and many parts of this large area are fertile land that remains uncultivated — the so-called green desert, not used by people and livestock. Most of the 39 countries affected by tsetse are poor, debt-ridden and underdeveloped.
The presence of tsetse and trypanosomiasis prevents:
- Use of more productive exotic and crossbred cattle livestock;
- Suppresses growth and affects livestock distribution;
- Reduces potential for livestock and crop production.
Tsetse flies transmit a similar disease to humans called African trypanosomiasis or sleeping sickness. An estimated 70 million people in 20 countries are at varying levels of risk, with only 3-4 million covered by active surveillance. Because the disease tends to affect economically active adults, many families remain well below the poverty line.
This is important! Increasing fundamental knowledge of how the tsetse fly interacts with its microbiota will enable new and innovative control strategies to be developed to reduce tsetse populations.
For several decades, the Joint Program has developed the SIT against the most important species of tsetse flies. It is used effectively where natural populations have been reduced by traps, insecticide-impregnated targets, livestock handling, and aerial application of sequential aerosol techniques.
Spreading sterile males throughout an area over many generations of flies can eventually wipe out isolated populations tsetse flies.