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PUBLIC RECORD OFFICE

Reference :-

TRITICO. 885

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

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Enclosure in No. 38.

A REPORT UPON INVESTIGATIONS INTO THE BIONOMICS OF GLOS

SINA, CONDUCTED IN UGANDA FROM NOVEMBER, 1913, TO APRIL, 1915, INCLUSIVE, BY WM. F. FISKE

Part

1.-"The Bionomics of Glossina palpalis."-A_review and synopsis of the results of investigations upon the Sesse Islands in Victoria Nyanza, and at points on the mainland shore.

Part II." Economic aspects of the problem presented by Glossina pulpalis in

Uganda."

Part III." The Bionomics of Glossina morsitans."-Results of preliminary

investigations conducted in Unyoro.

Part IV. "Miscellaneous Studies in Glossina Bionomics."-Details of the prin- cipal experiments, surveys, etc., made in the course of the investiga- tions, accompanied by maps, tables, and charts (to supplement Parts I. and II.).

Introductory

PART 1 THE BIONOMICS OF GLOSSINA PALPALIS.

Hosts and Host Preferences

The Following Habit

Protection:

(a) Breeding Grounds as Protection to the Puparia

(b) Shelter as Protection to the Adult

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Distribution as Determined by that of Hosts, and by Location of Water The "Natural Balance between Glossina palpalis and its liosts Conclusion to Part I.

INTRODUCTORY.

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The term bionomics" is here interpreted to imply the relations of the insect under investigation to its environment, and environment is held to include not merely climate, soil, drainage, topography, etc., but all the species of plants and animals which compose the local fauna and flora. These may be considered collect- ively, as they produce the environment characteristic of forest, bush, or grass land, or individually, as they may be hosts, prey, parasites, "friends," "enemies," or com- petitors of the particular species in question. These investigations have been largely concerned in an attempt to ascertain which among the features of its environ- ment directly affect Glossina palpalis for good or for ill.

2. The work has principally been conducted on the Sesse Islands, in Victoria Nyanza. These occupy a relatively small portion of the lake. They lie on both sides of the equator. Rain falls all months in the year, and the seasons are not sharply differentiated. Owing to altitude (8,700 feet) and the influence of the lake the temperature is equable and never excessive. In consequence the seasonal fluctuations in abundance of fly are much less than recorded for other regions, and insignificant when compared with those due to other causes (i.e., to differences in local environment).

3. Although there is little difference between the islands in climate, there is very much in other respects. In size they range from a few hundred yards to some forty miles in length, and they present great diversity in soil, drainage, and topog- raphy. These physiographic characteristics profoundly affect their faune and flora. Very few species are found upon them which are not common to adjacent portions of the mainland, but there are a great many on the mainland, both of plants and animals, and particularly of mammals and insects, which are not found on any island. Similarly, the larger islands support species not to be found upon the smaller, and upon the smallest both fauna and flora are extremely restricted. All but some of the smaller are infested by Glossina palpalis.

4. Open channels up to three hundred yards in width may be crossed rather freely by this fly, but if much wider they are a barrier to ordinary dispersive move. ments; consequently each infested island a half-mile or more from other land supports a colony, the welfare of which, unlike that of most of the semi-isolated colonies along

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the shore of the mainland, is so slightly as rarely to be measurably affected by outside influences. Each island must supply all that the species requires in all its stages and at all seasons of the year. Some are densely and others lightly infested. On some islands the colonies are large and strong; on others they are small, weak, and seemingly maintain a very precarious existence, that is to say. Degree of infes tation or local abundance is measured (in practice) by the number of flies (males) It varies on different islands which can be caught by a trained boy in one hour.

from less than 01 to more than 100. These variations are not due to season or to climate, but to differences in local environment. The islands are easily surveyed and compared one with another, so that the opportunities for observing the effect upon Glossina of the environment provided by each are ideal and probably unique. It was for this reason that they were selected for these studies.

5. Upon its environment the fly is dependent for two things only, food and protection; for, if adequately protected against all adverse influences, any insect will increase to a limit determined by its food supply.

HOSTS AND HOST PREFERENCES.

6. Nothing yet observed has indicated that in its distribution or local abun- dance the fly is affected by any other source of food than the blood of vertebrates, or that any other need be considered at this time for practical purposes.

7. The hosts indigenous to the islands which are known to be favoured by Glossina and which supply it with the greater part of its food are three: the crocodile, the monitor lizard (varanus), and the situtunga or marsh buck, which is the one antelope found upon them. There is a tortoise (not of large size) which is also favoured, but it is not common. Hippopotamus is probably fed upon, but first- hand information is lacking. The reptilian hosts are favoured to at least the same extent as the mammalian, and the fly can exist indefinitely upon them alone.

8.

In so far as the common indigenous animals are concerned, there seems to be a very sharp distinction between those which are favoured as hosts and those which are not. Monkeys are very common on some islands, and have frequently been seen foraging on the ground in densely infested localities, but they are not attacked, nor, so far as has been discerned, even approached, by the flies. Cormoránts and other large birds roost in enormous numbers on rocks and shrubbery just on or off the shore, and frequently nest in localities equally exposed to attack. Negative evidence only is available, but from the beginning this has consistently indicated that neither these The same nor any other birds are fed upon more than occasionally and irregularly. statement will apply to all mammals and reptiles which are indigenous to, and common upon, the islands other than those mentioned in the preceding paragraph. but no other mammal larger than monkey, otter, or mongoose is known,* and other reptiles larger than small lizards are rare.

9. Innumerable observations upon the behaviour of various animals toward fly, and of the fly toward them and toward man, have shown conclusively that the actual or relative immunity to attack enjoyed by some species is due as much to their repugnance to be fed upon as to any repugnance on the part of the fly to feed. Both factors, however, count. The fly is not attracted to certain animals, such as cor- morant and monkey, notwithstanding that these are larger, more common, more It is also active, and generally more conspicuous than either varanus or tortoise. very quick to leave any animal, even an individual of an attractive species, which is visibly annoyed at its presence. This is a very well marked characteristic, and of particular interest in several connexions.

10. Somewhat curious results come about in consequence of its possession. Two of them were Three young bulls were procured for experimental purposes. quite phlegmatic under attack of Glossina and Stomoxys (provided neither fly was too numerous), but were very uneasy if large Tabanids were present. If these were absent Glossina fed freely. but, if present. hardly at all. The third animal was of a spirited disposition, and objected to Glossina as well as to Tabanids, with the result that the other two were fed upon (all three were exposed together) fourteen and Seventeen times respectively more frequently than it.

11. Both goats and sheep used in similar experiments have resented the presence of Glossina. The sheep were rather more active in repelling it, and were

* Pigs are common on a few islands but they are not indigenous.