Trypanosome infections were monitored in three species of tsetse fly (Glossina pallidipes Austen, G. morsitans centralis Machado, and G. brevipalpis Newstead) at four locations in the Kagera River region of Rwanda from May 1989 to September 1990. Two of the four areas (Mpanga Ranch and Bukora Ranch) were subjected to tsetse fly suppression operations with odour-baited traps. Proboscis infections of the Trypanosoma congolense and T. vivax types accounted for roughly equal numbers of the 207 mature infections detected (3.8%). Variation in infection rates was area-specific rather than tsetse species-specific. Order of magnitude differences in tsetse fly densities among areas were not correlated with differences in infection rates at the start of tsetse fly suppression operations. Similarly, declines in population density on both control and experimental areas were not associated with significant changes in infection rates. The prevalence of trypanosomiasis in cattle at Bukora Ranch was not affected by a roughly 90% reduction in Glossina densities. T. congolense accounted for 79% of the infections at an overall prevalence rate of 5.5%. Trypanosomiasis in cattle persisted at extremely low densities of about 0.1 fly/trap/day. Treatment of cattle with diminazene aceturate (BereniP) suggested that many T. congolense parasites were drug resistant, and hence, were cycling among cattle due to the few Glossina present.

IntroductionThis paper briefly describes an experiment in the Lossitete Forest area of northern Tanzania (Irving et al., 1969) to compare the fly-round and Langridge-trap techniques of assessing populations of Glossina pallidipes Aust. before and after treatment of the area with pyrethrum from the air. The experiment was carried out in 1968 using aerial-spraying techniques previously described by Irving et al. (1969). Three spray applications were completed. In applications 1 and 2 an oil solution of 25% pyrethrum concentrate was diluted with power kerosene to give a final concentration of 0-4% w/v active pyrethrins; 2% piperonyl butoxide was added as synergist. For the third application, 5% DDT was added to the synergised pyrethrum solution. Methods Fly-round techniqueFlies were caught along a 9 400-yd fly-round at least twice a week by a group of men carrying a black cloth screen. Patrolling the fly-round by the catching party was started at the same time each day, but the finishing time varied depending on the numbers caught at each catching station. The persons in the catching party were changed as little as possible, and an attempt was made to eliminate the effect of time on the catch by starting the round at different ends on alternate days. Langridge-trap techniqueTwelve Langridge traps were used. The traps were first placed randomly in the experimental area and their positions were then changed till the most densely populated areas had been found. The trapping sites in the densely populated areas were regularly changed to eliminate the catching-out effect. The traps were inspected and emptied every weekday at about the same time, so that the catching period was the same for each trap every day. ResultsAssessment of the effectiveness of the pyrethrum applications was worked out by the fly-round technique and the Langridge-trap technique. Results for the fly-round technique are based on 72 flies (35 non-teneral males and 23 non-teneral females) which were caught before spraying, and 25 flies (8 non-teneral males and 6 non-teneral females), 46 flies (17 non-teneral males and 19 non-teneral females) and 57 flies (20 nonteneral males and 17 non-teneral females) which were captured after the first, second and third spray applications, respectively; the results for the Langridge-trap technique are based on 6 467 flies (1 430 males and 5 037 females) trapped before and 5 754 flies (1 308 males and 4446 females), 6 013 flies (1 362 males and 4651 females) and 13 310 flies (3 253 males and 10 057 females) trapped after the first, second and third spray (L 4683) c 2 2 2 C. S. TARIMO, C. W. LEE, J. D. PARKER and H. T. MATECHITABLE I. Percentage reductions in densities of G. pallidipes after pyrethrum applications from the air, as shown by fly-rounds and Langridge traps Fly-round technique Langridge-trap technique Application Non-teneral Non-teneral Teneral Total Males Females Total males females flies flies flies 1 78 74 21 64 9 12 11 2 52 18 29 36 5 8 7 3 43 26 -29 ---applications, respecti...

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