CO885-24 — Page 384

PUBLIC RECORD OFFICE

Reference :-

TTTIC.O. 885

24 PUBLIC RECORD OFFICE, LONDON

ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO

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Accordingly, a main objective of the work has been to settle the point. It was at first believed that a comparative study of a large number of the smaller islands would supply the desired information; if islands could be found upon which all recog nizable types of breeding places were absent, and if fly were present, it was assumed This, on the face of it, most that the question would be negatively answered.

good' reasonable assumption proved false; it developed that breeding places are only when they protect the puparia against animate foes as well as from adverse physical influences. There are very many kinds of places where puparia would incubate successfully as far as physical environment is concerned; there are many in which they would be safe from their enemies; there are not nearly as many where they are safe on both scores.

14. These enemies are not peculiarly inimical to Glossina palpalis; they do not specially seek its young in preference to other specics of dipterous puparia or other similarly helpless forms of insect life, and they are attached to a locality by the abundance of insect life in general, coupled with the proper physical environ- ment. So far as known they are principally insects themselves. But it is a fact that on all the islands, and more particularly upon the smaller, the insect fauna is greatly restricted as compared with the mainland, and amongst the species not represented are often some of the most conspicuous of the predatory foes of insect life in general. If the right ones chance to be included among the missing, any locality upon the island in question which happens to be physically suitable for the incubation of Glossina puparia becomes "good" breeding ground. This fact is no longer disputable, and, in view of it, the circumstance that small islands may be fly- infested if they happen to afford good shelter and good food, though lacking in recognizable types of breeding places, loses all significance.

15. With recognition of this fact the island survey was abandoned and a new A large island was found (Bugaba), with a method of study determined upon. coast line of some eighteen miles, along which shelter was fairly uniform and hosts quite evenly distributed. The effect of these two highly important factors in deter- mining degree of local infestation was thereby minimized, and variations in degree could fairly be attributed to some other environmental characteristic. The entire coast line was surveyed systematically for fly, and its local abundance was found to correspond very exactly to the presence and extent of easily recognizable types of Wherever they occurred the breeding places. These were few and scattered.

average abundance of fly for the entire island was exceeded; their influence extended for an indeterminate distance on either side, but, as distance from them decreased. the local abundance of Glossina invariably fell away, whatever the character of the The unavoidable conclusions, which subsequent foreshore in any other respect.

similar surveys confirmed, were that :-

(1) This species of Glossina is dependent upon the protection afforded by its "breeding places."

(2) If these are destroyed it will be no longer able to exist in the locality. 16. In the particular case of Bugaba Island the area which would require treatment, if breeding places were to be destroyed, represented only about 1 per cent. of the total, and a reduction by more than 90 per cent. of the area which it would be required to clear in a belt 200 yards in width encircling the island. The measure, as far as Bugaba was concerned, promised to be practical, efficient, and, as compared with any seriously proposed or hitherto contemplated, extremely economi- cal. It remained to put it to the final proof of actual experiment, and, in the first flush of success, it was desired to do this at the earliest possible moment.

17. With the planning of the experiment, however, unexpected and diverse difficulties were encountered. Positive and dependable results could not be expected if it were conducted on a small island; either a large island, like Bugaba, where it would be possible to show in advance that the distribution of fly correlated with that of the types of breeding places selected for treatment, or a reach of mainland shore, would have to be chosen as a site. If the latter, the experiment would have to be sufficiently extensive to preclude possibility of any considerable immigration of flies from over-populated breeding grounds beyond its limits; a reach not less than ten or fifteen miles in length would be required under actual existing conditions.

18. This condition could easily be met, but the next to come to attention pre- sented greater difficulties. Subsequent to the Bugaba survey it was shown, in the bionomic investigations, that if the marsh buck were generally common on a large island. (1) the dispersion of fly was conspicuously affected; (2) its breeding habits

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were modified; and, (3) even though a 200-yard belt were cleared to encircle the island, it was highly probable that fly might continue to exist independent of breed- ing places on the shore. These findings possessed the following double significance in connexion with any practical application of restricted clearing measures, which are only "practical" when they permit safe habitation of the formerly infested region: (1) mere occupation of an island overrun by marsh buck would pretty certainly result in driving this host of Glossina back to its stronghold in the swamp; that is to say, the effect of its presence on the fly would thus be done away with, and an experiment including actual reoccupation of such an island might succeed where one otherwise conducted might fail; (2) for all that could be said to the contrary an experiment involving reoccupation of an island not previously overrun by a favoured host of Glossina would fail, although one otherwise conducted might succeed. because man accompanied by his flocks and herds presents a new source of food supply, and might possibly play a similar rôle to that taken by the marsh buck. It was believed that man alone would not affect the habits and dispersion of the fly so profoundly, but this could not readily be proved. It was practically certain that sheep and goats would not serve as hosts; but the natives are large owners of cattle, and concerning these much doubt was felt. Experiments specially planned to determine the statics of cattle as hosts were inconclusive. The only con- clusions which could be reached, as far as the desired experiment was concerned, were that:

(1) It must include actual human occupation of the area selected.

(2) This must be normal occupation: i.e., fishing and long-shore work in canoes must be permitted, cattle herding not interfered with, etc. 19. Coupled with the conviction that only an extensive experiment, involving human occupation, would be worth the undertaking, a state of affairs gradually became manifest which rendered it doubtful if even this would be worth while. Unless it could be shown in advance that the minimum expenditure which would eertainly be necessary would not exceed the maximum which the natives would willingly pay (in labour or extra taxation) for the privilege of repossessing their fishing rights, etc., plus that which the Government could legitimately be called upon to disburse for the general welfare of Uganda as a whole, it was not proposed to to determine location and extent advocate the experiment at all. A "fly survey

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of breeding places was an essential preliminary in any event, and as conditions were studied on other islands than Bugaba and at points on the mainland, the minimum amount of clearing that appeared to be required too obviously exceeded that which the maximum expenditure economically possible would provide for. Any experi- inent having as its objective practically complete suppression of Glossina through attack directed against its breeding places looked more and more economically impracticable the more the actual situation was studied. The writer, however, was

fly survey wholly unwilling, on the one hand, to give up his original idea until a of several reaches of mainland shore should finally convince him of its imprac- ticability; and, on the other, to outline an experiment or in any manner to readvert to one based on destruction of breeding places until better assured that some hope of an economic solution of the problem lay in this direction.

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20. The shore of that part of Uganda known as Buddu was reported to be only lightly infested by Glossina, and to be practically fly free for long intervals, between colonies which were thus practically isolated. Acting on the advice of the Principal Medical Officer, this region was selected as probably the most favourable for the experiment, and at the earliest moment its systematic survey was begun.

21. To date (1st July) the results have been very satisfactory, though in many respects unexpected. Upwards of thirty miles of foreshore have been critically studied, and an almost continuous sand beach found along this entire distance. In previous experience sand beaches, if well sheltered, have invariably been found fly infested, and on the islands and mainland in Uganda proper they are never very extensive nor long continuous. But in Buddu the complement to the conditions described as existing on Bugaba Island has been found: i.e., mile after mile of con- tinuously good "breeding ground," but with shelter and food supply varying often abruptly. The Bugaba survey, conducted on a reach of shore where breeding ground was the variable, and food and shelter the constant, factors, demonstrated the depen- dence of fly upon this form of protection. The Buddu survey has filled what may as well be confessed was a long unfelt want, by demonstrating most clearly and con clusively the extent to which the fly, though provided with safe breeding places,