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244

No. 101.

REPORT OF THE GLOSSINA SUB-COMMITTEE OF THE IMPERIAL BUREAU OF ENTOMOLOGY.

SOME idea of the importance of the tsetse flies of the Glossina morsitans group as an obstacle to the development of Tropical Africa may be gathered from a con- In Southern Rhodesia, in which sideration of the wide areas over which they range. the fly-belts are comparatively small and have been more carefully surveyed than elsewhere, their extent has recently been estimated at 9,000 square miles. With reference to N.E. Rhodesia, Messrs. Kinghorn and Montgomery have expressed the opinion that it would be difficult to find a continuous area of fifty square miles free from G. morsitans anywhere except on the Serenje plateau, around Fort Jameson, In Nyasaland and on the high plateau between Lakes Nyasa and Tanganyika. probably more than a fifth of the area is infested by tsetse flies; while in Tanganyika Territory the fly-belts must cover nearly half the country. No precise information is yet available as to the extent of their range in British East Africa, Uganda, the Sudan, and the interior of West Africa.

2. Before any practical measures can be devised for the successful control of these dangerous insects, it is essential that we should know a great deal more than we do at present of their habits and life histories, and of the factors which favour their increase or inhibit their spread.

3. With regard to the habits of G. pallidipes and G. longipalpis we know practically nothing at present; but thanks to the work of various observers in Rhodesia and Nyasaland, a certain amount of useful information has been acquired with regard to the behaviour, breeding places, and parasites of G. morsitans; yet there still remain many important gaps in our knowledge.

4. The principal measures that have hitherto been recommended for the eradication of tsetse flies are:--(1) the wholesale destruction of the larger mammals; (2) the clearing of all small trees and undergrowth; (3) the continuous capture and destruction of the flies on a large scale; (4) the eradication of all natural breeding places, and the substitution of artificial ones, from which the pupa would be regu- larly collected, the flies emerging from them being killed and any parasites released; (5) the artificial breeding of parasites on a large scale, and the interchange of parasites from different parts of Africa.

5. Apart from various other inherent difficulties, all these proposals have one drawback in common, namely, that it is impracticable to carry them out effectively over large stretches of fly country. Nor are they likely to be of any real use in restricted portions of such areas, unless they are persistently maintained over a considerable period of time; for a relaxation of effort would almost certainly lead to a gradual re-infestation of the area. Thus, in the present state of our knowledge, it would seem that the adoption of such measures would be of little avail except where the cleared localities could at once be placed under beneficial occupation by settlers, who would maintain the disturbing factors that are inimical to the fly.

6. In the case of small and completely isolated fly-belts a combination of some or all of the foregoing methods of attack would probably be ultimately effective, if we may judge from the successful extermination of Glossina palpalis "in the island of Principe, in the Gulf of Guinea. But fly-belts of this character are very few and far between.

7. A more intimate knowledge of the bionomics of these insects will probably reveal the weak points at which they can be most effectively attacked; and these are more likely to be discovered, and with less loss of time, if a comprehensive series of observations and experiments can be carried out simultaneously in various localities throughout their range in which differing conditions of life are likely to

occur.

8. One of the primary requisites will be a thorough survey in each of these localities of the areas frequented by the different species; and these surveys will need to be checked at intervals throughout the year, in order to secure more exact information as to the seasonal and secular movements of the flies. In the course of these surveys the density of the fly should be estimated at frequent intervals on a standard basis, such as that adopted by Mr. Fiske and Dr. Carpenter for G. palpalis.

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SUGGESTIONS for ObservATIONS AND EXPERIMENTS. Distribution of the Fly.

What are the precise factors that determine the limits of a fly area?

Is there a marked contraction of the range of the fly during the height of the dry season!

If so, what are the special features of the localities in which the flies concentrate?

If a sufficiently small focus of this kind can be found, endeavour to exterminate the flies in it by every means and render it uninhabitable for them by clearing, burning, etc.; then carefully note the subsequent effects of these operations.

If the fly is absent from places that appear to be suitable and in which food is plentiful, endeavour to ascertain what are the adverse factors.

Effects of Clearing.

Does clearing actually kill the flies or merely drive them away?

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In the open "orchard bush so much frequented by G. morsitans is it sufficient

to clear away shrubs and branches of trees to a height of twelve or fifteen feet, or must trees of twenty to thirty feet be felled?

What is the minimum width of cleared belt that would effectively check the spread of the fly?

Study the best methods of maintaining clearings, by the planting of crops, by burning, etc.

Can the numbers of the fly be materially reduced by judicious burning of grass at times when food is scarce and shelter limited?

Compare the results obtained by indiscriminate clearing and by the clearing of breeding places after these have been defined.

What is the minimal degree of clearing which will render such a breeding place useless to the fly?

Breeding Grounds.

Make a detailed study of breeding places, noting their relation to soil, shade, surrounding vegetation, aspect, presence of food, proximity of water, etc.

Ascertain whether collections of puparia placed in unusual situations are

more liable to destruction than in natural breeding places.

If so, what are the enemies that take advantage of the alteration? What are the factors that safeguard the normal breeding grounds?

Test the effect of destroying natural breeding places and establishing artificial

>nes from which the puparia are regularly removed.

Can the attractiveness of an artificial breeding place be enhanced by means of special odours, etc.?

Ascertain the precise relation of breeding to season by the periodical exami- nation of selected areas.

Food of the Fly.

Test the food preferences of the various species of Glossina.

Are any of them absolutely dependent on any special species of mammals?

Is there a critical breeding period during which a marked reduction in the food supply would seriously check reproduction?

Do the flies seek their food by sight or scent? and does the presence of long grass prevent them from finding their hosts?

Destruction of Adults.

Test various methods of killing and trapping the adult flies on a large scale for a prolonged period-not less than a year.

Endeavour to ascertain how long the flies live in nature by releasing large numbers of marked individuals and re-catching them at intervals.

Parasites.

Try whether it is possible to breed local parasites in very large numbers, using the puparia of common and nearly related flies that can be easily reared in the laboratory.

Test the possibility of introducing additional parasites of different kinds from remote parts of Africa.

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