The scientific basis of the control of Glossina morsitans by game destruction / by the Trypanosomiasis Committee of Southern Rhodesia.

  • Southern Rhodesia. Trypanosomiasis Committee.
Date:
[1945?]
Catalogue details

Licence: In copyright

Credit: The scientific basis of the control of Glossina morsitans by game destruction / by the Trypanosomiasis Committee of Southern Rhodesia. Source: Wellcome Collection.

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    captive flies have been induced to probe specially-warmed grapes, and one eminent scientist (G. D. H. Carpenter) from an examination of the gut contents of G. palpalis formed the opinion that tsetses do sometimes suck water or plant juices. But Carpenter’s paper was published in 1913, and since then the theory that tsetses can sustain life only on blood has been so strengthened that it is now unassailable. Swynnerton, on p. 228 of his monumental book, “‘The Tsetse Flies of East Africa,’ published in 1936, speaks for all research workers on tsetses when he says: “‘To sum up, tsetses of both sexes depend on blood for their meat and drink and probably on nothing else.” At the present time work on the nutrition of tsetses is mainly concerned with preferences for different kinds of blood, and to some extent with the physiology of biood digestion. It has been noted, for example, that certain special biological adaptations associated with an exclusive blood diet are characteristic of tsetse flies. These include the loss of certain ferments which are necessary for the digestion of carbohydrates (e.g., the starch of plants), a great increase in other ferments which are necessary for the digestion of proteins (e.g., nitrogenous food present in blood), and the acquisition of factors preventing the coagulation of blood so that the insect can suck it. Food Preferences of Tsetse Flies. Realisation that tsetses depend on blood, and that deprivation of such food must bring about their extermination, has caused much attention to be given to the subjects of whether all vertebrates can act as hosts, and if not, whether destruction merely of those most favoured as hosts would suffice to rid an area of tsetses. It was soon found that captive laboratory-bred flies show little discrimination; when hungry and otherwise in the right mood they will feed on almost any mammal, bird or reptile against which the gauze-covered mouth of their container is pressed. Wild flies, however, are not thus given easy access to all manner of animals, and there is much evidence to show that each species of tsetse feeds most frequently on those animals that are dependably accessible. Thus Glossina morsitans, as it ranges along the edge of a vlei, may see and smell any of a wide range of the more conspicuous mammals, or if it comes on none of these it may find a large bird, such as a vulture, stork or ground hornbill. G. pallidipes, on the other hand, does much of its hunting along the game tracks which traverse the thicket where it lives, and thus makes much more contact with bush-pigs and bush- buck than is usually made by G. morsitans. Yet another tsetse, G. palpalis (not found in Southern Rhodesia) feeds mainly on crocodiles and monitor lizards. Considerable work has also been carried out using the precipitin test for the identification of animal blood in the tsetse and by direct measurement of ingested blood corpuscles to determine the species of animals used by the tsetse as hosts. An indirect way of determining whether any particular species of mammal is normally preyed upon by tsetses is by determining its reactions to inoculations with the trypanosomes transmitted by tsetses. If it is found that a wild mammal is susceptible to trypanosomiasis in the way that domestic animals are susceptible, it is obvious that that animal is not a common host of tsetses. Thus purely nocturnal animals, like antbears and porcupines, and certain small diurnal animals like hyraxes, monkeys and the smallest antelopes, are so little resistant to trypano- somiases when tested in the laboratory that it is certain they cannot be regular hosts of tsetses.