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SOME OBSERVATIONS ON THE BIONOMICS OF GLOSSINA PALPALIS 

 ON THE ISLANDS OF VICTORIA NYANZA. 



By H. Lyndhurst Duke, M.D., D.T.M. & H. (Camb.), 

 Government Bacteriologist, Uganda Protectorate. 



On arriving at Nsazi Island on Victoria Nyanza in July 1918 to carry out some 

 experiments with Glossina palpalis and rinderpest, I was at once struck by a marked 

 diminution in the numbers of the fly on this and the neighbouring islands. Since 

 the days of the first Commission of the Royal Society, the small island of Kimmi, 

 about three-quarters of a mile N.E. of Nsazi, has been noted for the numbers of its 

 tsetse. I had with me some of the original Mpumu fly boys and others who had 

 worked on these islands with Fiske and Carpenter from 1911 to 1916. Their 

 evidence on such matters is reliable, as they receive a bonus for their catches. They 

 were all unanimous that the fly on Kimmi, Nsazi, and Tavu Islands had decreased 

 very markedly in numbers. My own observations confirmed this in each case. 



On looking around to discover the cause for the diminution, one outstanding fact 

 was at once apparent. During the recent rise in level, which attained its maximum 

 in June 1917, the Lake invaded, and in places completely covered, the great majority 

 of the sandy beaches especially favoured by the fly for the deposition of larvae. 



The requirements given by Carpenter in his Progress Report (1) as constituting 

 the favourite sites of G. palpalis pupae are : — (a) shade and free air circulation ; 

 (6) dry and loose soil, commonly gravel or coarse sand. 



The most favoured breeding grounds of the fly in this northern group of the Sesse 

 Islands were those of Damba and Tavu Islands. Although Carpenter's latest Progress 

 Report is not available, I believe he refers therein to the Tavu pupa ground as second 

 only to that of Damba. Pupae had also been found on Kimmi, Nsazi and Bulago 

 Islands, though in no great numbers. 



In the course of July 1918 I visited all these islands and in each case, except perhaps 

 that of Bulago Island, foimd that the rise in the level of the lake had materially 

 curtailed the extent of suitable sandy breeding area. 



Tavu Island. 



The greater part of the sandy area patronised by the fly in former years is 

 now covered with a thick layer of black mud, dotted here and there with floating 

 water-weeds. The " byansambwe " bushes (Triumfetta macropJiylla), which were 

 formerly plentiful on this beach, have been largely washed away by the water. The 

 " nzibaziba " {Acalypha)* shrubs, hardy though they are, have also suffered. Both 

 these plants are commonly found associated with the favourite pupa grounds of the 

 fly. At this breeding ground, the water's edge in July 1918 was still some 40 yards 

 landward of the high- water level of 1911 ; and much of the zone exposed by the 

 receding of the water since November 1917 is covered by a boggy mixture of black 

 mud and the remains of the old sand. 



* Mr. E. Fyfie, Chief Forestry Officer, kindly identified these plants. 



