114 RUPEET W. JACK. 



Conditions in the dry Season. 



Dr. H. Lyndhiirst Duke, of Uganda, in a recent paper* refers to the dry season as 

 a time of stress and reduced breeding rate for the fly in that territory. Lloyd's 

 records concerning Northern Rhodesia are quoted as parallel observations, although 

 the latter's statement to that effect applied only to the earher part of his work in the 

 Luangwa Valley (Bull. Ent. Res. iii, p. 234) and his later work on the plateau led to 

 exactly the opposite conclusion, namely that breeding was practically confined to 

 the warmer part of the dry season (Bull. Ent. Res. v, p. 58). Lamborn in Nyasaland 

 has made several statements on this point. For instance, in his Third Report on 

 Glossina Investigations in Nyasaland (Bull. Ent. Res. vii, pp. 29-50) on page 30 we 

 have the statement : " The small number of Hving pupae is to be accounted for by 

 the breeding being at its minimum during the late dry season " (July). On page 36 he 

 states : " Now as the dry season draws to a close pupae are being produced more 

 freely;" and on page 46, " The breeding season for G. morsitans is in full swing, just 

 as the rains are about due." It would seem that the period when the dry season 

 *' draws to a close " and " the rains are about due " might without inaccuracy be 

 •described as " the late dry season " in preference to July. Nevertheless Lamborn's 

 •contention is quite clear, namely that the breeding season is at its minimum in July, 

 and is in full swing in October, when the first rains may be anticipated both in 

 Northern and Southern Rhodesia. In Southern Rhodesia, however, the October 

 rains are normally very local and may not occur at all, and dry season conditions 

 frequently prevail well into November. October and November (before heavy rains 

 set in) are well known as the hottest months of the year and the term " latter part of 

 the dry season " would appear naturally to include the period from the beginning of 

 August to the opening of the heavy " planting " rains, which usually commence about 

 mid-November. In some seasons they are, however, postponed until well into 

 December, and in such circumstances, as the veld still maintains a dry season 

 character, observations on breeding rates, etc., are still influenced by late dry season 

 conditions, and this should be made clear. 



Observations on the seasonal breeding rate in Southern Rhodesia are insignificant 

 compared with those in Northern Rhodesia and Nyasaland, owing to the fact that 

 no officer has been available to devote even the bulk of his time to the tsetse-fly 

 problem. There is not the least doubt, however, that the fly may, under favourable 

 conditions, breed very freely during the latter and warmer part of the dry season 

 {August to November). Observations at Sipane Vlei, abeady published, leave no 

 doubt upon that point. It would seem therefore that conditions in Nyasaland, and 

 Northern and Southern Rhodesia are similar in this respect, at least as regards the 

 plateaux. In Uganda on the other hand the published records of rainfall in the 

 Masindi area and at Mpumu show that the chmate is very different, the dry season 

 being much less clearly marked and of much shorter duration. 



In 1911 the writer called attention to a marked difference in the distribution of fly 

 in the dry and wet seasons.f The dry season haunts of the fly in Southern Rhodesia 

 have been described more than once. They consist of centres where shady evergreen 



*Bull. Ent. Ees. x, p. 20, fines 11-13, and elsewhere. 

 fBull. Ent. Res.'u, pp. 357-361. 



