Teneral Glossina morsitans centralis were fed on the flanks of African buffalo, N'Dama or Boran cattle infected with Trypanosoma vivax IL 2337. The infected tsetse were maintained on goats and on day 25 after the infected feed, the surviving tsetse were dissected to determine the infection rates. The mean mature infection rates (% ± S.E.) in the tsetse fed on buffalo, N'Dama and Boran cattle were 34·3 ± 9·9, 33·7 ± 13·4 and 58·9 ± 7·1, respectively. Logistic regression analysis indicated that infection rates in the labrum and hypopharynx of the tsetse were significantly lower when fed on the infected buffalo or N'Dama than Boran cattle. Similarly, the risk of infection was significantly lower in male than female tsetse. When teneral G. m. centralis, G. pallidipes, G. p. gambiensis, G. brevipalpis and G. longipennis were fed simultaneously on either the buffalo cow, the N'Dama bull or the Boran steer infected with T. vivax IL 2337, the mature infection rates were higher in the two morsitans group than the two fusca group tsetse, whilst G. p. gambiensis was relatively refractory to the infection, irrespective of the host species on which they fed. Logistic regression analysis indicated that the infection rates in the labrum and hypopharynx were significantly different amongst the five tsetse species for each of the three infected host animals. Nevertheless, the trypanotolerant African buffalo and N'Dama cattle may serve as reservoirs of T. vivax infection as can trypanosusceptible Boran cattle.

Six genera of bacteria: Serratia, Providencia, Enterobacter, Aeromonas, Cedecea and Bacillus were isolated from field-collected G. pallidipes. Four genera: Serratia, Providencia, Enterobacter and Aeromonas were isolated from insectary-reared Glossina morsitans morsitans. All bacteria except, Bacillus spp. and Providencia alcalifaciens were pathogenic for teneral G. m. morsitans. Bacteria isolated from insectary-reared tsetse were more pathogenic than those isolated from the field. Fungi of three genera were also isolated from field-collected adult G. pallidipes, Penicillium, Aspergillus and Fusarium. Five genera, Aspergillus, Penicillium, Rhizopus, Mucor and Trichoderma were isolated from field-collected G. pallidipes pupae. The fungi, however, were only mildly pathogenic for adult tsetse and were not pathogenic for pupae.

Trials using deltamethrin impregnated odour-baited targets for control of tsetse, have been running in Galana Ranch on the coastal hitherland since 1986. In July 1988, a similar trial was started in Lambwe Valley, Western Kenya. Glossina pallidipes is the sole vector in the valley and is present in very high densities.

In Galana Ranch trial, octenol and acetone are used as odours while in Lambwe Valley, natural cow urine is used in addition to acetone and octenol. Tsetse population densities were assessed weekly for 3 weeks, before deployment of targets and thereafter at monthly intervals. A herd of cattle is used to monitor the effect of the control measures on disease incidence.

On Galana Ranch, the block where the initial trial began has remained free of G. pallidipes for a period of 3 years. In a period of 9 months in the second year of the trial, the berenil index in a herd of cattle was 0.07 in the controlled area compared to 2.5 in the uncontrolled area.

In Lambwe Valley a 99.9% reduction in trap catches has been observed in most parts of the park at the end of the first year. The berenil index in the cattle has dropped from 6.3 to 0 and there is a general improvementin the health of the animals. Observations are continuing at both sites.

Tsetse flies have been eradicated from an area of 48,000 km2 in Zimbabwe since 1981. The main approach has been pesticidal control, involving ground spraying, aerial spraying, cattle dipping and artificial bait techniques, in some circumstances in combination. This represents a change in tactic from the pre-independence period when control relied solely on ground spraying. Factors which have influenced choice of technique are discussed in the paper, including scale of trypanosomiasis problem, technical limitations of the technique, cost-effectiveness and environmental considerations.

Ground spraying, the mainstay of tsetse control operations in Zimbabwe prior to 1980, is becoming increasingly unfavourable because of high logistical requirements and environmental reasons, but remains an effective technique under a wide range of circumstances. Aerial spraying has proved very effective for management of crisis situations but is comparatively expensive, capital intensive in hilly terrain and less effective against Glossina pallidipes than G. morsitans. Vector control by applying insecticide (deltamethrin) to cattle appears technically feasible at a very competitive cost. This is a most promising technique in areas where there are already cattle and few wild hosts.

Control of tsetse using odour-baited and insecticide-treated screens has proven technically feasible in a wide range of terrain, and appears economically competitive with ground spraying. Both technical and financial performance of the technique are still being improved. Bait technology offers scope for the new approaches to the control of the fly and defence of cleared areas from reinvasion.

After the rinderpest panzootic of the late last century, Southern Mozambique appeared to have become free of Glossina morsitans and G. pallidipes. However, since the 1940s a gradual advance of tsetse into Southern Mozambique has been observed. Anti tsetse measures were taken during the 1950s and 1960s along the southern front of the tsetse belt to stop the advance of the fly into tsetse free cattle grazing areas.

To reassess the extent of the fly front in Inhambane Province, a tsetse survey using bait oxen was made in the Muabsa area during 1981 and 1982. G. m. morsitans, G. pallidipes and G. austeni were found, although not always sympatrically. It appeared that the G. morsitans and G. pallidipes front in the study area had been stable since 1969. The front is situated along a line of marked changes in soil and vegetation types and it is concluded that this may be the reason why these tsetse did not advance further south. G. austeni was found throughout the study area in a less well defined belt. The populations of G. m. morsitans and of G. pallidipes in the study area form the most southerly distributed populations of these species known in Africa today.

Mixed T. congolense and T. brucei appeared in mice when proboscis from 3 field collected G. pallidipes were individually inoculated into mice. One of these flies had earlier been shown by dissection, to have T. congolense and the other two had T. brucei infection. A comparison of the growth rates of T. congolense and T. brucei in mice revealed that T. brucei always overshadowed T. congolense. These observations highlight the significance of multiple trypanosome infections in the epidemiology of African trypanosomiasis.

Trypanosome infection rates in tsetse, Glossina pallidipes Austenin five areas along the Kenya coast were studied for 2 years (1980–1982). The total percentage infection rates were 12.62, 7.24, 9.50, 7.86 and 7.97 for Ukunda, Diani, Muhaka, Shimba Hills and Mwalewa, respectively. The respective values for males were 3.13, 4.16, 5.17, 5.03 and 8.13. Overall there were more trypanosome infections due to; Trypanosome congolense followed by T. vivax and T. brucei, although these varied among the localities. The age of the flies, their feeding patterns and regular use of chemoprophylaxis in local cattle were the main factors affecting infection rates.

In the Zambezi Valley of Zimbabwe, ULV applications of non-residual insecticide (endo-sulphan and NRDC 161) were made to a 1.8 × 1.8 km block of woodland infested with Glossina morsitans morsitans Westw. and G. pallidipes Austen. The recapture rates of marked flies released in the centre of the block, and recaptured in odour-baited traps in and around the block, indicated that the insecticides killed about 97% of flies that had been released 1–4 hr before spraying. Catches of unmarked male G. m. morsitans in the centre of the block declined after the insecticide applications, but there was no clear effect on catches of female G. m. morsitans and both sexes of G. pallidipes. Data for the movement of marked flies suggested that the minimum daily rates of movement were about 700 m for male G. m. morsitans and about 800 m for the other tsetse. An increase in dawn temperatures, from 17.5 to 27.5°C, was associated with an increase in the rate movement of G. pallidipes in the early morning. The failure to detect changes in the unmarked populations of female G. m. morsitans and both sexes of G. pallidipes was attributed to the high mobilities of these flies and demonstrated that unmarked populations could not be studied satisfactorily in small plots; studies based on marked populations are recommended for such plots.

Three morphological classes of haemocytes (prohaemocytes, plasmatocytes and granulocytes) were observed in the haemolymph of Glossina morsitans morsitans and G. pallidipes. In addition to the three types, a category of spindle cells were also observed in haemolymph especially in the newly emerged Glossina. Based on their unusual morphology, as well as on their inverse relationship with the number of thrombocytoids (a filamentous plasmatocyte), it is suggested that these spindle cells might be precursors of thrombocytoids observed mostly in older Glossina. The number of thrombocytoids increased progressively with the increasing age of the flies. Total haemocyte counts (THCs) dropped significantly during the first 48 hr following emergence, after which the values levelled off with the exception of minor fluctuations. This sudden drop in THCs resulted primarily from a remarkable decrease in the number of the spindle cells in the haemolymph. The number of round plasmatocytes decreased gradually and progressively with age of the flies, while the number of the granulocytes increased, suggesting a possible transformation of plasmatocytes into granulocytes. Newly emerged female G. morsitans morsitans were observed to have significantly higher THCs (P < 0.01) than males of the same age. Although no difference was observed between THCs of 5-week-old pregnant and non-pregnant female G. morsitans morsitans, the differential haemocyte counts (DHCs) showed that the concentration of thrombocytoid fragments was significantly lower (P < 0.01) in the pregnant than in the non-pregnant females.