Between 1990 and 1999, at Rekomitjie Research Station, Zambezi Valley, Zimbabwe, 29,360 female G. pallidipes were dissected to determine their ovarian category and trypanosome infection status. Overall prevalences were 3.45 and 2.66% for T. vivax and T. congolense, respectively, declining during each year as temperatures increased from July – December. Fits to age-prevalence data using Susceptible-Exposed-Infective (SEI) and SI compartmental models were statistically better than those obtained using a published catalytic model, which made the unrealistic assumption that no female tsetse survived more than seven ovulations. The improved models require knowledge of fly mortality, estimated separately from ovarian category distributions. Infection rates were not significantly higher for T. vivax than for T. congolense. For T. congolense in field-sampled female G. pallidipes, we found no statistical support for a model where the force of infection was higher at the first feed than subsequently. The long survival of adult female tsetse, combined with feeding at intervals ≤3 days, ensures that post-teneral feeds, rather than the first feed, play the dominant role in the epidemiology of T. congolense infections in G. pallidipes. This is supported by estimates that only about 3% of wild hosts at Rekomitjie were harbouring sufficient T. congolense to ensure that tsetse feeding off them take an infected meal, so that the probability of ingesting an infected meal is low at every meal.

Environmental temperature is an important driver of the population dynamics of tsetse (Glossina spp) because the fly's immature stages are particularly vulnerable to temperatures (T) outside the range T = 16–32°C. Laboratory experiments carried out 50 years ago provide extensive measures of temperature-dependent rates of development, fat consumption and mortality in tsetse pupae. We improve on the models originally fitted to these data, providing better parameter estimates for use in population modelling. A composite function accurately models rates of pupal development for T = 8–32°C. Pupal duration can be estimated by summing the temperature-dependent daily percentage of development completed. Fat consumption is modelled as a logistic function of temperature; the total fat consumed during pupal development takes a minimum for T ≈ 25°C. Pupae experiencing constant temperatures <16°C exhaust their fat reserves before they complete development. At high temperatures, direct effects kill the pupae before fat stores are exhausted. The relationship between pupal mortality and temperature is well described by the sum of two exponential functions. Summing daily mortality rates over the whole pupal period does not reliably predict overall mortality. Mortality is more strongly correlated with the mean temperature experienced over pupal life or, for T ≤ 30°C, the fat consumption during this period. The new results will be particularly useful in the construction of various models for tsetse population dynamics, and will have particular relevance for agent-based models where the lives of individual tsetse are simulated using a daily time step.

A rapid, visually read, dot-ELISA developed for the detection and differentiation of trypanosome species in tsetse flies (Glossina spp.), was field tested alongside the standard fly dissection method on a ranch in south eastern Kenya. Of 104 G. pallidipes dissected, 2 were found to be infected with trypanosomes in their midguts. By the dissection method the infecting trypanosome species could not be identified, as both flies had no salivary gland infections. However, using the dot-ELISA, the 2 flies were shown to be infected with Trypanosoma congolense in their midguts. The midguts of an additional 6 (5·8%) of the 104 G. pallidipes tested positive for T. congolense in the dot-ELISA, even though no trypanosomes were seen on dissection. The infection rate for this fly species as determined using the dot-ELISA, therefore, was 7·7% for T. congolense in midgut infections compared to 1·9% identified by fly dissection. The salivary glands and mouthparts of the 6 additional tsetse flies identified by dot-ELISA were all negative as determined by the 2 techniques. None of 390 G. longipennis flies dissected and examined for trypanosomes in the midgut, salivary glands and mouthparts was shown, by this method, to be infected. Using the dot-ELISA, however, 17 (4·4%) of the flies tested positive for T. congolense in the midgut, whilst the salivary glands and mouthparts of the same flies were negative. Thus, the dot-ELISA appears to be more sensitive than the fly dissection method under field conditions. Moreover, the dot-ELISA can be performed in the field without electricity. It is simple to perform, and was not affected by high ambient temperatures (22–32°C), or by contamination of reactants with dust.

Salivarian trypanosomes pose a substantial threat to livestock, but their full diversity is not known. To survey trypanosomes carried by tsetse in Tanzania, DNA samples from infected proboscides of Glossina pallidipes and G. swynnertoni were identified using fluorescent fragment length barcoding (FFLB), which discriminates species by size polymorphisms in multiple regions of the ribosomal RNA locus. FFLB identified the trypanosomes in 65 of 105 (61·9%) infected proboscides, revealing 9 mixed infections. Of 7 different FFLB profiles, 2 were similar but not identical to reference West African Trypanosoma vivax; 5 other profiles belonged to known species also identified in fly midguts. Phylogenetic analysis of the glycosomal glyceraldehyde phosphate dehydrogenase gene revealed that the Tanzanian T. vivax samples fell into 2 distinct groups, both outside the main clade of African and South American T. vivax. These new T. vivax genotypes were common and widespread in tsetse in Tanzania. The T. brucei-like trypanosome previously described from tsetse midguts was also found in 2 proboscides, demonstrating a salivarian transmission route. Investigation of mammalian host range and pathogenicity will reveal the importance of these new trypanosomes for the epidemiology and control of animal trypanosomiasis in East Africa.

A midgut trypanolysin and an agglutinin from Glossina palpalis subspecies were isolated and partially characterized using anion-exchange chromatography and polyacrylamide gel electrophoresis. FPLC fractions of midgut extracts of Glossina palpalis palpalis caused agglutination and lysis of two trypanosome species (Trypanosoma congolense and Trypanosoma brucei brucei). although Glossina palpalis gambiensis caused only agglutination. The trypanolysin and agglutinin were active only in the posterior midguts, were heat labile above 50%C, had a periodic cycle of ‘activity’ in response to bloodmeal intake and were not affected by protease inhibitors or trypsin but were inactivated by pronase. The lytic substance contained two proteins with approximate molecular weights (Mr) of 12000 and 10000 Da respectively. The agglutinin had an approximate Mr of 67000 Da. Gamma-irradiation of the two subspecies caused a temporary inhibition of trypanolytic and agglutinin activities in midgut extracts.

The recent development of analytical models of trypanosomiasis has increased the general applicability of models to the strategic control of the disease. An analysis of detailed data on tsetse abundance and infection rates and trypanosome prevalence in village-based trypanotolerant cattle over 4 years in The Gambia showed that seasonal patterns of abundance in Glossina morsitans-infested areas were consistent, and that the rates of trypanosome infection remained relatively unchanging. However, there were two distinct seasonal trypanosome prevalence patterns in cattle, with peaks occurring either in May/June/July or November/December. The peaks of trypanosome prevalence therefore occurred either 4 months before or after the times of peak challenge from G. morsitans, not 1 or 2 months after as predicted by analytical models. In G. palpalis-infested areas there was little seasonal variation in abundance or trypanosome infections, but peak trypanosome prevalence still occurred mostly in June/July. Despite the incongruity between the months of peak prevalence and challenge, the overall annual prevalence rates and tsetse challenge indices showed a significant linear relationship. It is concluded that existing analytical models need to be refined to take into account trypanotolerance and the various influences on the expression of this trait.

In Zimbabwe, studies were made of the numbers of tsetse (Glossina spp.) and stable flies (Stomoxys spp.) attracted to cattle of different nutritional status, age and sex. Host odours were analysed to determine the physiological basis of these differences and improved methods are described for measuring rates of production of kairomones. Seasonal fluctuations in host weight, related to changes in pasture quality, had no significant effect on attraction of tsetse or Stomoxys. However, both attraction to different individuals and carbon dioxide production by these individuals were strongly correlated with weight, suggesting a possible link. Attraction to the odour from different types of cattle decreased in the order ox > cow > heifer > calf, and oxen were twice as attractive as calves of less than 12 months old. Lactation did not alter the relative attractiveness of cows. Calves less than six months old produced lower levels of carbon dioxide, acetone, octenol and phenols than oxen, but for older calves and cows, levels of production of known kairomones and repellents were similar to those of an ox. Carbon dioxide produced by cattle varied according to time of day and the animal's weight; cattle weighing 500 kg produced carbon dioxide at a mean rate of 2.0 l min−1 in the morning and 2.8 l min−1 in the afternoon compared to respective rates of 1.1 and 1.9 l min−1 for cattle weighing 250 kg. Artificially adjusting the doses of carbon dioxide produced by individual cattle to make them equivalent did not remove significant differences in attractiveness for tsetse but did for Stomoxys. Increasing the dose of carbon dioxide from 1 to 4 l min−1 in a synthetic blend of identified kairomones simulating those produced by a single ox, increased attractiveness to tsetse but not to the level of an ox. The results suggest that the main sources of differences in the attractiveness of individual cattle are likely to be variation in the production of carbon dioxide and, for tsetse, other unidentified kairomone(s). The biological and practical implications of these findings are discussed.

We have previously described a bloodmeal-induced molecule (lectin-trypsin complex) from the midgut of the tsetse fly, Glossina longipennis, with both lectin and trypsin activities (Osir et al., 1995). In this paper, we report on the isolation of a similar molecule from the midguts of Glossina fuscipes fnscipes and provide direct evidence for its involvement in the development of African trypanosomes. The molecule (native Mr ∼65,700) has two non-covalently linked subunits, Mr ∼28,800 and Mr ∼35,700. The native molecule was found to be capable of inducing differentiation of bloodstream-form trypanosomes into procyclic (midgut forms) in vitro. In the assays, specific antibodies against procyclin were used to monitor the transformation of the bloodstream-form trypanosomes into procyclic forms. This induction was specifically inhibited by D-glucosamine. Cis-aconitate was also capable of inducing the transformation process with the same efficiency as that of the lectin-trypsin complex. While increasing the concentrations of the lectin-trypsin complex (≥100 μg protein/ml) in the incubation assays resulted into higher transformation rates, it also led to high parasite mortality. These results provide evidence for the involvement of the midgut lectin-trypsin complex in the differentiation of bloodstream-form trypanosomes within tsetse midgut.

Trypanosomes in the dissection-positive proboscis of Glossina pallidipes were identified by PCR using species-specific primers. Of the 3741 flies dissected 643 were proboscis positive. PCR was performed on 406 dissection-positive probosces giving positive identifications in 352 (86·7%) and infection rates of 14·8% for congolense-type infections, 2·8% for vivax- type infections and 1·4% for the unidentified group. Of the 352 PCR identified infections 225 were single, 111 were double, 13 were triple infections and there were 3 quadruple infections. Statistical analysis suggests that mixed infections group into 3 largely separate divisions among the tsetse population (i) Trypanosoma congolense savannah and T. congolense Kenya coast, (ii) T. simiae, T. congolense Tsavo and T. godfreyi and (iii) T. vivax. We conclude that either differing feeding patterns among members of the fly population or the ability of the trypanosomes in each of the infection categories to significantly influence the maturation of trypanosomes in the other categories are the most likely causes of the groupings noted. Chi-squared analysis of dissection and PCR methods of trypanosome identification revealed profound differences (χ = 19·1; D.F. = 1; P > 0·05). If confirmed in other studies these findings have serious implications for our understanding of trypanosome epidemiology in tsetse flies, much of which is founded on data from dissection-based trypanosome identifications.

Post-mesocyclic development of Trypanosoma brucei in the tsetse fly in its migration from midgut to salivary glands, was revisited by sequential microdissection, morphometry and DNA-cytofluorometry. This development started by day 6 after the infective feed, with passage of mesocyclic midgut trypomastigotes through proventriculus and upward migration along foregut and proboscis to the salivary gland ducts. Kinetics of salivary gland infection showed that colonization of the salivary glands by epimastigotes occurred only during the time-limited presence of this developmental phase in the foregut and proboscis. Post-mesocyclic trypanosomes in the foregut and proboscis were pleomorphic, with 4 morphological stages in various constant proportions and present all through from proventriculus up to the salivary gland ducts: 67% long trypomastigotes, 27% long epimastigotes, 4% long epimastigotes undergoing asymmetric cell division and 2% short epimastigotes. Measurements of DNA content demonstrated a predominant tetraploidy for 67% of these trypanosomes, the remainder consisting of the homogeneous diploid short epimastigotes and some long epimastigotes. According to the experimental data, the following sequence of trypanosome differentiation in the foregut and proboscis is proposed as the most obvious hypothesis. Incoming mesocyclic trypomastigotes (2N) from the ectoperitrophic anterior midgut start to replicate DNA to a 4N level, are arrested at this point, and differentiate into the long epimastigote (4N) which give rise, by an asymmetric cell division, to 2 unequal, diploid daughter cells: a long, probably dead-end long epimastigote and a short epimastigote. The latter is responsible for the epimastigote colonization of the salivary glands if launched at the vicinity of the gland epithelium by the asymmetric dividing epimastigote.

The design and construction of the Nitse trap are described. The materials required are: royal blue cotton, black cotton, mosquito netting, brass pipe, metal rods and galvanised wire. The cutting and joining of the various parts to produce the trap and the method of placement are also described. Finally a rough estimate of the cost of the trap is given.

The diurnal resting sites of Glossina palpalis palpalis were studied from October 1981 to December 1982 in the human trypanosomiasis focus at Bouafle (Ivory Coast). A total of 1382 resting tsetse (970 males and 412 females), were found after 757 hr of search in their natural habitats.

At any season, over 80% of the flies were resting on lianas (Acacia pennata in particular), on coffee trees (Coffea indica) and on Eupatorium odoratum.

Almost all the flies showed a preference for resting on the underside of woody parts of plants selected. The heights of the resting sites ranged from 10 cm to 2.5 m above the ground and their diameters ranged from 0.1 cm to 8 cm. It must be stressed that both in the dry and in the rainy seasons, more than 50% of the flies rested below 50 cm from the ground and over 90% of these favoured stems and branches measuring less than 3 cm in dia.

In the vegetation surrounding villages or along the main access roads and bush pathways, G. p. palpalis were found resting at 1 m to 5 m from the edge of its vegetation habitat.

About 27% of flies were engorged or showed at least red blood meals in their guts. The catching of resting flies therefore, appears to be an excellent way of collecting fresh blood meals for identification of the natural vertebrate hosts of G. p. palpalis in the study area.

The practical interest of the study is discussed and recommendations made for the selective application of residual insecticides in the tsetse habitats to control the vectors of sleeping sickness in the Bouafle focus.

The distribution of 31 Glossina spp. and subspecies belonging to fusca, palpalis and morsitans groups is given for 38 African countries. The natural hosts of 17 tsetse species and subspecies from many areas within different regions of Africa are also given. These were collated from the results of both published and unpublished work, for the period 1953 to 1991 inclusive, comprising altogether 47, 697 bloodmeals. This review is aimed to provide current knowledge on the distribution as well as the natural hosts of tsetse.

The effect of resettlement programmes and agricultural development projects on the tsetse population in Gambella were investigated. Adult tsetse were collected using biconical traps and moving vehicle catches. The species collected were Glossina pallidipes, G. fuscipes and G. tachinoides. G. pallidipes was the most frequently encountered species. G. morsitans which were reported to be abundant in the area (Balis and Bergeon, 1968; Hutchinson, 1971; Langridge, 1976) were not collected during the present survey.

About 155,000 ha. of land, formerly reported as tsetse infested, is found to be tsetse free. The natural vegetation is being transformed into farmlands and villages, and the wildlife is being hunted out, remaining only in such areas as Demesaye and Gog forest.

Under such circumstances tsetse hosts may change from wild mammals to man and his domestic animals and outbreaks of nagana and sleeping sickness are likely to occur throughout the region.

The relationships between estimates of tsetse challenge and trypanosome prevalence in trypanotolerant and susceptible cattle were examined at sites of the African Trypanotolerant Livestock Network. Estimates of tsetse challenge were determined as the product of tsetse relative densities, their trypanosome infectionrates and the proportions of feeds taken by them from cattle. Trypanosome prevalence in both trypanotolerant and susceptible breeds of cattle was estimated from monthly examination of groups of ear-tagged cattle. Regression equations between estimates of trypanosome prevalence and tsetse challenge were fitted using an arcsin transformation of trypanosome prevalence and a log10 transformation of tsetse challenge. Highly significant relationships between estimates of tsetse challenge and trypanosome prevalence were found for sites with trypanotolerant cattle (P < 0.0001) and sites with susceptible cattle (P < 0.01). Mean trypanosome prevalence at a given level of tsetse challenge was at least twice as high in susceptible as in trypanotolerant cattle. The slopes of the regression lines for the two groups of cattle were significantly different (P < 0.05). The results confirm the superior ability of trypanotolerant cattle to withstand tsetse challenge in the field. The curves obtained for the two groups of cattle illustrate the necessity in tsetse control campaigns for a major reduction of tsetse populations to take place before significant decreases in trypanosome incidence in livestock can be achieved.

Tsetse colonized either for laboratory studies or for release in S. I. T. programmes are assumed to be healthy and geneticallyw similar to flies in natural populations. However, insect colonies are subjected to many of the same evolutionary forces that influence genetic changes in natural populations, i.e. drift, selection, hitch-hiking, mutations, assortative mating and immigration. The influence of these on genetic structure of tsetse fly colonies is outlined, and examples are presented from several species. There is little or no evidence for adaptation during the early phases of laboratory colonization of five species of tsetse. A model is presented indicating that with as little as a 5% fitness difference between males, some colonies have existed long enough to have undergone significant changes in the relative numbers of males having “standard” and “enhanced” fitness. Slight changes in heterozygosity of colonized flies is documented by comparing colonies and field-collected flies and by comparisons within colonies over periods of several generations or years. An example of hitch-hiking is illustrated with the closely linked genes Sr (sex ratio) and Est-X in Glossina morsitans submorsitans. A possible interaction between alleles at these loci is discussed. A summary is presented of polyacrylamide gel electrophoretic methods for monitoring 16 polymorphic loci distributed among the X chromosome and autosomes of tsetse.

Plotting the movement of air through typical tsetse habitats in Zimbabwe revealed that it is liable to change direction by over 90° within a few metres. In winds of < 1 m/sec, there was a negative correlation between windspeed and the wind's tendency to meander, whether in thick bush or out in the open. And at the mean windspeed of wet season mopane woodland (0.3 m/sec), the wind changed direction by c. 15°/sec. Accordingly, host odour does not move downwind in simple trajectories that tsetse flies could easily follow. Even 5 m from a source, odour (modelled with smoke) approached a notional tsetse fly for a quarter of the time from >90° away from the true source direction. Also, air turbulence at common tsetse resting sites generates much nonsense information about the “true” direction of any odour-bearing wind. The suggested answer to how tsetse manage to find distant, invisible hosts, in spite of this confusing information from the wind, is that they progress by a biased random walk which is the outcome of their upwind anemotactic responses to odour-bearing wind and the proportion of the time for which the wind does blow in the “correct” direction. Computer simulation shows that this might work in principle.

Fly catching experiments using the biconical trap and a vector collector (under mosquito net) were performed in different biotopes of the forest zone in Côte d'Ivoire (Daloa region).

Of the three species of tsetse usually caught, Glossina palpalis, and to a very minor degree Glossina pallicera, was attracted to man. G. palpalis showed vis-a-vis man a clear difference in attractiveness according to the point of capture. In those habitats where hosts were rare and dispersed (gallery forest, coffee and cocoa plantations) this species frequently attacked man who came into contact with it during the accomplishment of his usual activities, whereas in the village it voluntarily abandoned him in preference for pigs. Whatever the type of biotope, the trap had the same attractiveness. Its use, in contrast to captures on man, enabled a simultaneous study of diverse species that co-existed anthropophilically or zoophilically.

Although almost all the tsetse taken in the trap or on vector collector were hungry, it was noticed that the number of females in the trap samples was always higher than that of males.

Behavioural-antennal responses of tsetse to buffalo urine, which has been identified as a potent olfactory attractant, were investigated. Tsetse Glossina morsitans morsitans rapidly raised their antennae upon stimulation with the odour of buffalo urine. Flies showed a clear preference for the undiluted urine, though antennal responses even to 100,000 × diluted urine were significantly different from control, indicating the high efficacy of the attracting compounds present in it. Fresh buffalo urine was the most attracting as compared to 4- and 8-day-old urine. The dichloromethane extract of fresh urine was as active as the natural product, indicating that the attracting compounds were extractable into dichloromethane. Under laboratory conditions, responses of males to the urine were significantly more than females.

Sounds produced in relation to the sexual behaviour of the tsetse, Glossina m. morsitans, were investigated. During mating, a receptive virgin female adopted a relatively passive role while the male produced sound and drummed her with the tarsi of the meso- and metathoracic legs upto about 4–5 min immediately after mounting. During the long cppulatory phase, the male only produced sound when the female became restless or the pair was disturbed. No sounds were produced during the ejaculatory phase after which the flies separated.

Immediately after separation, the females were often receptive for further short copulations, but were completely unreceptive 24 hr later and showed vigorous repellent behaviour. The post-copulatory behaviour patterns and the rejection behaviour of the female were also accompanied by sound production. Although males readily mated with freshly killed females with the usual mating behaviour, sound production was less intense than when the females were live.

Mating sounds were composed of frequencies up to 50 kHz with the exception of the sounds produced by males, while mating with freshly killed females which not only lacked any ultrasonic components, but were also of low intensity. The most dominant frequency was centered between 1.5 and 2.5 kHz. Peaks were also observed between 0.5 and 0.8 kHz, around 5 and 9 kHz. On the basis of intensity, it is suggested that the frequency components below 10 kHz carry the most important part of the acoustic signal.