110 



in mind the rapidly fatal result of exposure to direct sunlight, it is 

 rather remarkable that in the semi-darkness of the jars shaded by thick 

 brown paper a temperature of 40-41C. should have had a more 

 serious effect on the tsetse-flies than in jars shaded by the various 

 coloured papers. In one typical experiment with a fly in a jar shaded 

 by thick brown paper signs of distress were noticed after 35 minutes, 

 and the fly was dead after a further exposure of 25 minutes " 



As regards the colour preference exhibited by Glossina morsitans, 

 Professor Newstead and Dr. J. B. Davey (107) have recorded the results 

 of experiments carried out in Nyasaland in 191 1 . " During the month 

 of October/' they write, " one of us made a series of observations on 

 ten different days to test the colour preference of this tsetse-fly. For 

 this purpose natives were provided with vests of the following colours : 

 (1) white (clean) ; (2) bright canary-yellow ; (3) red ; (4) khaki ; 

 (5) dark blue ; the bare back of a native being used as a control. The 

 results were that khaki headed the list for attractiveness, and in a 

 diminishing sequence red, blue, bare back of a native, and white ; 

 no flies were seen upon the yellow garment. Dirty white vests were 

 subsequently found to be much more attractive than clean ones. 

 Furthermore, the buff-green canvas such as used for machilla coverings, 

 bags, tents, etc., was found to be quite as attractive as the khaki." 



It was also noted by Dr. Warrington Yorke that khaki-coloured 

 clothing, though excellent as a shooting kit, appears to attract G. 

 morsitans in large numbers. 



INFLUENCE OF ODOURS. Bagshawe and Austen (5) have pointed out 

 that it would be highly interesting to discover whether, in their selection 

 of a breeding place, Tsetse-flies are in any way influenced by odours, 

 or whether, as Mr. LI. Lloyd believes in the case of G. morsitans, the 

 principal factor in the choice is the existence of a relatively dark 

 hiding-place, to which the female insect resorts during the period of 

 gestation. The odours that attract insects are not necessarily per- 

 ceptible to the human nostril ; if, therefore, the breeding places of 

 G. palpalis and G. morsitans do not appear to us to give off a definite 

 smell, it does not follow that such an odour cannot be detected 

 by the pregnant Tsetse-fly. In India some years ago it was found by 

 the late Mr. F. M. Howlett that Stomoxys calcitrans will oviposit upon 

 cotton-wool impregnated with valerianic acid, one of the acids occurring 

 in fermenting vegetable matter, in which the eggs of this fly are natur- 

 ally deposited. It may be that on analysing the humus in Tsetse-fly 

 breeding places some substance or essence having specially attractive 

 properties would be found in it, and such a discovery might be turned 

 to account in establishing artificial breeding places a matter that we 

 shall have to discuss later on (see p. 146). 



CHAPTER XII. 



MEANS OF LIMITING AND DESTROYING TSETSE-FLIES. 

 PREDATORY ENEMIES OF TSETSE-FLIES. 



The search for means of limiting or destroying Tsetse-flies is a matter 

 of exceptional importance, since the discovery of such means would 

 at least enable us to check the progress of human and animal trypano- 

 somiases. It would also render cattle-breeding possible in immense 

 tracts of Africa (as in Northern Rhodesia, parts of Nyasaland and 



