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PUBLIC RECORD OFFICE

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885/26

PUBLIC RECORD OFFICE, LONDON

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is not, on a great scale, practicable. If, therefore, the preliminary investigations should show that no insuperable difficulties are present (a) of an administrative nature, (b) as regards cost, I hope very much that I may be allowed to attempt the experiment.

5, Grenville Place, S.W.5,

30th January, 1923.

885

No. 49.

C. F. M. SWYNNERTON.

COLONIAL OFFICE to BRITISH SOUTH AFRICA COMPANY.

Downing Street, 2nd March, 1923.

SİB,

WITH reference to the letter from this Department of the 15th of January,* I am directed by the Duke of Devonshire to request you to inform your Directors that the reportt forwarded with your letter of the 15th of December last‡ on the game destruction experiment between the Gwaai and Kana Rivers has now been considered by the Managing Committee of the Imperial Bureau of Entomology.

2. The views of the Committee are expressed in the enclosed memorandum. It will be seen from paragraph 6 that the Committee have formed the opinion that the evidence put forward does not satisfactorily demonstrate that game destruction alone offers an inexpensive and practicable method of controlling tsetse-flies over wide areas; and the Secretary of State feels sure that when the considered views of this expert body are such as the memorandum indicates, your Directors will recognize the importance of proceeding with the utmost caution in the matter.

3. As regards the question of financial assistance raised in the last paragraph of your letter under reference, the Secretary of State regrets that it is not practicable for a contribution to be made by His Majesty's Government towards the cost of the *experiment.

"I am, &c..

Enclosure in No. 49.

C. T. DAVIS.

Memorandum on the Report on the Game DestrUCTION EXPERIMENT IN SOUTHERN RHODESIA.

1. THE report of the Chief Entomologist. Southern Rhodesia, dated 20th October, 1922, with the covering Minute by the Director of Agriculture, dated 3rd November, 1922, on the experiment for the extermination of tsetse-fly by the destruction of game between the Gwaai River and Kana River, has been referred to the Managing Committee of the Imperial Bureau of Entomology.

The Committee, having considered these papers, desire to offer the following observations.

2. One of the most striking features of the report is the fact that, although game destruction has been in progress for three previous seasons, there was a marked increase of big game in certain portions of the area of operations in the fourth season, so that the number of animals shot in the fourth year was actually greater than in any preceding year. These facts sufficiently demonstrate that effective game destruction is a much more difficult and complex problem than its advocates would have us suppose, nor do the explanations for this irruption of game, advanced by Mr. R. W. Jack, in any way counteract this view.

3. That a reduction in its food supply would sooner or later cause a reduc tion in the numbers of the fly itself might readily have been taken for granted without any expensive experiment, but the benefit secured will be temporary, unless the area dealt with is immediately placed under effective settlement; otherwise. the cost of game destruction may have to be borne indefinitely in order to check the periodical re-incursions of game that will take place. The actual eradication of the fly by this means is a very different matter, and there is no reason to suppose as a result of the present experiment that such eradication can be effected by this means.

* 885: not printed. ! No. 48.

62028: not printed.

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4. From a scientific point of view the manner in which the evidence for the reduction of the fly is put forward is far from satisfactory. Mr. W. F. Fiske long ago pointed out that catches of flies at different places or at different times in the same place cannot yield any reliable evidence as to the relative density of the fly, unless the figures are presented in a standarized manner which he fully explained. Out of six sets of comparative figures, the Fiske formula had been used for one only, in the other cases there is nothing to show how long the catching lasted or how many collectors were working, with the result that the figures lose most of their value.

5. Again, another important and possibly vitiating factor has been ignored, namely, the meteorological conditions. It is well known that Glossina morsitans is much less in evidence on dull than on sunny days, and wind also tends to make them less active. If, for example, the weather in one October was mainly hot and sunny, and that in the following October mainly windy and overcast, one would expect to get a reduction in the number of flies caught in the second October, even though the insects were really just as numerous.

of

any

6. It is difficult to see how any really useful or reliable conclusions can be arrived at by Mr. Jack's method of making a brief annual inspection of the experimental area for a fortnight in the month of October only. The unreliability deductions based on the comparison of catches on a single day at intervals of a year is sufficiently illustrated by Table 7 of the report; for, whereas Mr. Jack secured only two males at the Bira River (number of catchers and nets not stated), two days earlier Dr. Nobbs and Mr. de Buys without a net secured seventeen males and seventeen females at the same place. Table 7 alone suggests a progressive annual diminution of the fly; whereas Dr. Nobbs' experience indicates that such a conclusion may be quite erroneous.

Unfortunately, in the carrying out of these game destruction operations, the opportunity of securing scientific data that might have had some practical importance seems to have been lost. In the first place, a thorough survey should have been made of the distribution of the game and the fly before the destruction began, for without this no really sound deductions can be made as to the effects of the shooting. Further, such surveys should have been made periodically, especially in relation to the seasonal movements of both game and fly; and the influence of meteorological con- ditions and different types of vegetation on these movements should also have received ⚫ attention. Although a passing reference is made to the effect of the great drought of 1921 on the game, its possible direct affect in reducing the numbers of the fly has been entirely ignored in considering the captures made in 1922.

In general, therefore, the Committee are of opinion that the evidence put for- ward does not satisfactorily demonstrate that game destruction alone offers an inexpensive and practicable method of controlling tsetse flies over wide areas.

7. Apart from the foregoing considerations, the recent reports by Dr, FL. Duke (see Proceedings of Royal Society, Series B. Volume 94, No. B. 660. 1st January, 1923), and Mr. C. F. M. Swynnerton (see Bulletin of Entomological Research, Vol. XIII, Part 3), on the epidemic of sleeping sickness in the Tanganyika Territory, both put forward very cogent arguments for the view that, in certain conditions. the destruction of game on a large scale may result in a serious danger to the health of the human population in the vicinity. In the circumstances the Committee venture to think that it would be unwise for any Government in Tronical Africa to adopt the policy of wholesale game destruction where there is any reason to suspect the existence of sleeping sickness.

8. In conclusion, the Committee desire to express their appreciation of the fact that those who were entrusted with the task of currving out the experiment had to face many serious difficulties, often at some personal risk.

22332

No. 50.

REPORT ON THE COLI FCTING OF INSECT PARASITES FOR NEW ZEALAND. A. FIELD WORK.

The Common Earwig.

THE collecting of Earwigs, with the purpose of obtaining from them any insect parasites for New Zealand, began on 4th September last. And from that ilate until the end of November the work was continued almost daily.

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