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(g) Relations between Glossina and other large biting flies. (Large biting flies, such as Tabanus, are deprivative enemies of tsetse, because they cause the host to become restive.)
(A) Super-density of Glossina. (If the flies become too numerous they become the deprivative enemies of each other, and density must be reduced.)
Table XXXIV-Indicating that super-density of fly on Kimmi Island led
to reduction in rate of reproduction and decreased density. Table XXXV-Supplementary to above, showing slight decrease in density, and great increase in female percentage, correlated with increase in rate of reproduction.
X.--General Conclusions :—
The range and density of tsetse are controlled by the coincidence of life requisites. These are:-
(1) Food, consisting of vertebrate blood;
(2) Protection, consisting of: (a) breeding-grounds required by pupæ; and
(b) shelter required by adult.
All three life requisites must occur within the radius of range or reach of individual flies. The more closely they are in juxtaposition the more favourable the conditions of life; the more widely they are separated the less favourable are conditions of life; if separated beyond certain distance conditions of life become intolerable and the species cannot exist.
Density is governed by the quantity of the least abundant requisite within reach of the others: as by quantity of food within reach of the flies from protec- tion, or by the quantity of either form of protection within reach of flies from the others and from food. It can be most economically and efficiently controlled arti- ficially by further depriving the flies of the least abundant requisite (which may be any one of the three, according to local conditions and circumstances).
The question of "natural enemies " is of very slight importance, because the pro- tection of "shelter" and "breeding-ground" is required against inanimate as well as animate destructors, and with rare exception, serves against all destructive agencies alike. Innumerable "enemies" lie in wait beyond the protected precincts, but with the rarest exceptions never penetrate these precincts.
The economic or injurious status of the fly is controlled by numerous It would easily be factors, which operate independently of density. possible to reduce density by depriving the flies of food, and by the same process to increase the injurious status of the insect. It is thus dangerous, on the one hand, to undertake "suppression" of the insect or to "fight it" without taking into full account the factors controlling its injurious status, and necessary, on the other hand, to take these into full account in order to devise the most economical measures for reducing its injurious status.
XI-Supplementary: Fluctuations in Level of Victoria Nyanza as they affect
Range and Density of Tsetse :—
(a) Fluctuations in level of lake from 1904 to 1913.
Graph IX.-Illustrating same.
(b) Observations.-Effect of fluctuations on shelter and breeding-grounds of
tsetse.
(c) Fly survey.-Effect of fluctuations on range and density of Glossina palpalis.
Graph X.-Illustrating excessive variations in density occurring between 1906 and 1915, and due to recession of lake and growth of sheltering vegetation on sandy shore in Buddu Saza.
Excerpts from the manuscript report of Dr. Van Someren, describing con- ditions in Buddu Saza in 1906, and comparison with conditions at the same point in 1915.
(d) Causes for fluctuations in lake level.
(e) The probable effect of a dam at the outlet of the lake on infestation of its ahores by tsetse.
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No. 87.
MINUTES OF THE TWENTY-THIRD MEETING OF THE FINANCE SUB-COMMITTEE OF THE IMPERIAL BUREAU OF ENTOMOLOGY, HELD AT THE Colonial Office on the 22nd of May, 1919, at 2.30 p.m.
Present:
DR. HARMER (Chairman).
SIR D. PRAIN.
DR. MARSHALL,
MR. DOWNIE (acting as Secretary).
1. THE minutes of the previous meeting* were confirmed.
2. Dr. Marshall laid before the Sub-Committee his Annual Reportt for the year 1918-19.
In summarizing the present financial position of the Bureau, Dr. Marshall observed that a deficit of £200 was expected at the end of the present year. He then raised the question of the extension to the staff of the Bureau of the new scale of war bonus recently approved by the Treasury for members of the Home Civil Service. He explained that the Committee had approved the applica- tion of the old Treasury scale of war bonus, and that he had received recently several applications from individuals for the grant of war bonus at the increased rate. He stated that if the grant of war bonus was approved at the new rate with effect from the 1st of April, 1919, the anticipated deficit of £200 would be increased to over £800. The Sub-Committee agreed to recommend that the new scale of war bonus should be adopted with effect from the 1st of April, and should remain in force until the meeting of the proposed Conference, which would consider the whole financial position of the Bureau, or until the Treasury modified the existing rates, whichever date should be the earlier.
The Sub-Committee agreed to recommend that the Director should receive war bonus on the new scale, in common with other members of the staff of the Bureau.
3. The Sub-Committee next considered an application which had been received from Mr. J. J. Simpson, late Entomological Expert to the West African Colonies, for the grant of war bonus on the West African scale for the period from the 1st of January, 1917, to the 22nd of August, 1917, when the period of his engagement in West Africa terminated. The Director pointed out that during the period in question no members of the home staff of the Bureau were in receipt of war bonus, and, further, that during part of that period (from March to August), Mr. Simpson was not in West Africa but was on leave in this country.
The Sub-Committee decided that they were unable to recommend the application for approval.
4. The Director mentioned that Mr. Waterston had been permitted to join the Army, and had been serving in Macedonia on the understanding that, during his absence his salary of £300 per annum should be paid to his wife, and that he should refund to the Bureau any sums which he was able to save from his Army pay He stated that Mr. Waterston had after meeting his out-of-pocket expenses.
saved a sum of £400, and he suggested that it would be fair and reasonable that The Sub- Mr. Waterston should be called upon to refund only £300 of this sum. Committee agreed to recommend this proposal.
* No. 84.
+ Annexure to No. 88.