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3. Mr. Churchill stated in his despatch of the 20th of December, 1921, that he would be glad to give most careful consideration to any proposals for local investigations of this nature which might be submitted by your Government, and I can assure you that I shall be no less ready to entertain suggestions made for extending the work which has already been put in hand whenever any of the Governments concerned are in a position to propose such extension.
I have, &c.,
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Enclosure in No. 52.
DEVONSHIRE.
INVESTIGATIONS INTO THE BIONOMICS OF TSETSE-FLIES DURING
1921 AND 1922. MEMORANDUM BY THE DIRECTOR.
THE following is a brief summary of the work that has been done in connexion with tsetse-flies during the past two years in the various British possessions in Africa.
In
Union of South Africa. The only species of any practical importance in this area is Glossina pallidipes. Investigations into the distribution and life-history of this insect have been carried on by Mr. R. H. Harris, of the Division of Entomology in Zululand, but no comprehensive report on the subject has yet been issued. a brief interim report Mr. Harris expresses the opinion that organized thorough grass-burning would materially diminish the numbers of the fly; if, further, the game were reduced to such a level that it ceased to provide food for a large number of flies, attention could then be concentrated on the destruction of the limited number of breeding-places of the fly that would remain; so that elimination might possibly be effected by a judicious combination of these three factors.
Indiscriminate destruction of game has been continued in Zululand for the protection of the recently settled farming area in the vicinity of the Game Reserve; but no information appears to be available as to the precise methods adopted or as to the effects that have been produced upon the game and the fly.
In Swaziland about 160 square miles of the Game Reserve have quite recently been thrown open to shooting, and Blue Wildebeest has been removed from the category of Royal Game. It is supposed that these measures will serve to prevent the spread of the nagana disease of cattle from Zululand into Swaziland.
Southern Rhodesia. In this territory the fly of outstanding importance is G. morsitans. The game destruction operations that have been carried out against it for the last four years during the dry season only, on the north bank of the Shangani River, have recently been terminated. The local authorities are satisfied that these measures have been successful in effecting a material diminution of the larger game animals and have thus checked the tendency of the fly to spread back to the areas south of the river, which it occupied prior to the rinderpest epizootic of 1896.
The Chief Entomologist, Mr. R. W. Jack, has secured the services of an assistant entomologist, Mr. Chorley, who is devoting all his time to the study of the bionomics of Glossina. He is at present working on the Umniati River, North- West Mashonaland, and has there found that two species of Bombyliid flies are acting as very efficient parasites of G. morsitans, although these same flies appear to be of little importance in Nyasaland, where they also occur. No report on the investigation has yet been published.
Nyasaland. Here again G. morsitans is the only significant tsetse-fly. Dr. W. A. Lamborn has continued his investigations into the parasites of this species, with a view to devising some method of utilising them on a practical scale. He has now ascertained that the minute wasp, Syntomosphyrum glossing, which was previously supposed to attack other insects that parasitise Glossina, is really itself a very useful primary parasite of the tsetse-fly. It has been found that this insect will breed quite freely in the laboratory, and if the necessary conveniences are available it should not be difficult to obtain it in thousands. Fortunately, it breeds readily in the pupa of various common Muscid flies, including the house-fly and blow-fly, so that the strain can be maintained even when tsetse pupæ are unprocurable. The time spent by the parasite within the pupa of its host is about four weeks, so that it can easily be sent by post to any place that can be reached within that time. Since, according to present information, Glossina tachinoides
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appears to be remarkably free from parasites in Nigeria, attempts will shortly be made to send a series of consignments of Syntomosphyrum there by way of Madeira, the Canaries, and England. It also should be worth a trial in other parts of East and South Africa.
It is not to be assumed that any species of Glossina is likely to be controlled by means of this parasite alone; but there is good reason to suppose that it may prove useful as an additional line of attack in conjunction with other measures.
Tanganyika Territory-In this area both G. morsitans and G. pallidipes are very widely spread, and now a new species, G. swynnertoni, has been shown to be of serious importance as a carrier of human trypanosomiasis.
Owing to the discovery of an epidemic of sleeping sickness due to Trypanosoma rhodesiense in the Mwanza District early in 1922, Mr. C. F. M. Swynnerton made a valuable investigation into the entomological aspects of the position in and around the infected area. He found that the tsetse-fly implicated (G. swynnertoni) was feeding very persistently on human beings and was actually resident in many of the bush villages. He has shown good reasons for supposing that this condition had been brought about by rapid recent diminution of the game, due partly to military operations and partly to heavy destruction by natives as a result of famine; the flies were thus driven to concentrate on man, and this probably caused the outbreak. The character of the bush was found to be quite as important a factor as game in determining the presence of tsetse-flies, the species of the morsitans group being specially dependent upon thickets, the growth of which is much encouraged by early and incomplete burning of the grass, and is a characteristic of cultivated lands that have been abandoned." The value of close grazing, whether by cattle or antelopes, as a means of keeping down such thickets is emphasized, and it is con- sidered that the browsing habits of elands would be particularly useful in this connexion.
Mr. Swynnerton was specially impressed with the automatic effect of concen- 'trated human settlement in eradicating tsetse-flies, and suggests the possibility that local surpluses of men and cattle might by organization and inducement be diverted to the suppression of tsetse belts. He regards the abolition of small villages in tsetse-haunted bush as most desirable, where possible, combined with closer settle- ment on the outskirts of the bush, which would thus be gradually invaded and rendered unsuitable for the support of tsetses. His published report (Bulletin of Entomological Research, vol. XIII, pt. 3, January, 1923) contains much useful infor- mation and many practical suggestions towards a solution of the tsetse problem.
Uganda. Recent work in this Protectorate has been almost entirely confined to Glossina palpalis.
Mr. W. F. Fiske has continued his work in connexion with the gradual resettle- ment of the proscribed tsetse-fly zone on the shore of Lake Victoria, which appears to be progressing satisfactorily. This constitutes an important experiment in the reclamation of tsetse-infested territory by means of organized human settlement. As a result of his experience Mr. Fiske is in complete accord with Mr. Swynnerton in regarding controlled settlement as the soundest method of eliminating tsetse- flies, and both observers have shown reasons for concluding that withdrawal of population from areas threatened by these flies simply leads to an extension of their range
and renders their ultimate.control still more difficult.
For a period of twelve months Dr. G. D. H. Carpenter carried out an experi- ment on two small islands in Lake Victoria to test the possibility of controlling G. palpalis by the construction of artificial breeding places from which the puparia would be regularly collected. Such breeding places actually proved to be much more attractive to the flies than three natural ones that were kept under observation as controls; but although many thousands of puparia were secured, no appreciable difference was observed in the number of flies present, and Dr. Carpenter concluded that this measure by itself was not likely to be of much practical utility.
One of the islands of the Sesse group has been sown with efwatakala grass to test its supposed efficacy in driving away tsetse-flies, but the results have not yet been recorded.
Nigeria. In the Northern Provinces, where alone tsetse work is in progress. G. tachinoides, G. palpolis and G. morsitans are the only important species.
Drs. W. B. Johnson and Ll. Lloyd have completed a rapid survey of those Darts of the Northern Provinces in which the distribution of tsetses was not well known, occupying ten months. Much valuable information as to food habits and trypanosome infections was secured by the dissection of large numbers of flies, viz.,
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