A survey to establish the distribution of tsetse flies (Diptera: Glossinidae) in southern Sudan was conducted using biconical traps. Only Glossina fuscipes fuscipes was caught. The results obtained revealed a further northern advance of G. f. fuscipes of c. 29 km along River Bahr el Jebel and 48 km along River Luri, and a southern contraction of Glossina morsitans submorsitans belt from Lewis' distribution limit. Glossina f. fuscipes was encountered in gallery forest along water courses with no significant differences in sex ratios and proportions of tenerals and non-tenerals between trap catches (P>0.1). Flies were absent from villages and open savanna woodland forests away from water courses. Trap catches were significantly higher during wet than dry season (t = 2.681; P < 0.025), although flies could be caught in any one location during both seasons. These results are discussed in relation to the current epidemic of human African trypanosomosis (HAT) in southern Sudan.
