Homidium bromide is a broad-spectrum anti-microbial trypanocide likely to be encountered as a violative residue in blood collected from abattoirs destined for feeding laboratory-reared tsetse colonies. We investigated its effects on longevity of laboratory-reared Glossina morsitans morsitans Westwood. Four steers were intra-muscularly administered with 1 mg homidium bromide/kg of body weight and blood was aseptically collected from them between 15 and 30 min post-administration. This blood was defibrinated, analysed for homidium levels, screened for bacterial contamination, frozen and warmed to 37°C before feeding to tsetse flies. Teneral male (100) and female (220) G. m. morsitans flies were fed on homidium-treated diet, and control flies (99 males and 187 females) on untreated blood diet and their survival monitored for 163 days. Homidium, at 266.15 ng/ml blood diet, significantly (P < 0.05) improved fly survival. We concluded that homidium bromide has a beneficial effect on tsetse, probably attributable to its antimicrobial activity against unfavourable microbes mediated by the drug, and could be used as a tsetse diet additive.

The present study was undertaken to determine the occurrence of virus particles in male accessory reproductive glands and to describe the changes in the affected tissues. Using electron microscopy techniques, it was possible to identify rod-shaped virus-like particles in accessory reproductive glands of male tsetse, Glossina morsitans morsitans Westwood. The viruses occurred intracellularly within the epithelial cells and in the lumen of the glands. Cell degeneration characterized by abundant clear vacuoles, membrane-bound vesicles, disorganization and elimination of cell organelles typified the infection. The inference, therefore, is that virus infection may be primarily responsible for the necrotic changes identified in the gland cells. It is suggested that the lesions caused in the gland epithelium by the infection would disturb the glandular cells and disrupt synthesis of the secretion. This may eventually destroy the male accessory reproductive glands leading to inability of the male flies to form spermatophores for transferring spermatozoa to the female tsetse. Lack of sperm transfer would consequently result in no egg fertilization.

Transmission experiments were conducted to compare the transmissibility of genetically different Trypanosoma congolense (Savannah subgroup) strains isolated from cattle in a trypanosomiasis endemic area of eastern Zambia. A total of 17 strains were compared. Three strains were extremely virulent with a short pre-patent period, high parasitaemia and a short median survival time (between 5 and 9 days) in mice. The remainder of the strains belonged to the moderate (6 strains) or low (8 strains) virulence categories with median survival times between 10 and 30 days and >30 days, respectively. Batches of 40 teneral Glossina morsitans morsitans (Diptera: Glossinidae) were offered a single bloodmeal on mice infected with one of those strains. Flies were dissected to determine their infection status 21 days later. The proportion of flies with procyclic and metacyclic infections differed significantly between trypanosome strains and were significantly higher in flies infected with extremely virulent strains (P=0·033 and P=0·016 for the differences in the procyclic infection rate of strains with moderate and low virulence, respectively and P=0·005 and P=0·019 for the differences in the metacyclic infection rate of strains with moderate and low virulence, respectively). On the other hand, moderately virulent strains had, in general, higher procyclic and metacyclic infection rates compared to low virulent strains. But the differences were not significant (P>0·05). The outcome of those experiments shows clear differences in transmissibility of trypanosome strains associated with their virulence. This observation confirms the theory for the evolution and maintenance of virulence in a parasite population and may explain the persistence of virulent trypanosome strains in a susceptible host population.

Investigations were conducted to establish field responses of Glossina pallidipes, G. m. morsitans, muscoids and tabanids to castor, raw linseed, paraffin and chlorinated paraffin oils in deltamethrin suspension concentrate (sc) formulation, through randomised Latin square experiments. Tsetse landing responses on targets treated with 400 ml/m2 of any of the oils in 2 g/m2 deltamethrin formulation were significantly lower than on non-oil-containing deltamethrin formulations, for both G. pallidipes (F(4,32) = 4.855, P = 0.00357) and G. m. morsitans (F(4,32)=2.421, P = 0.06862).

The landing response indices, relative to the control formulation without oil, were 0.60, 0.70, 0.61 and 0.41 in G. pallidipes and 0.92, 0.82, 0.75 and 0.42 in G. m. morsitans and for paraffin, chlorinated paraffin, castor and raw linseed oils respectively. Glossina pallidipes and G. m. morsitans landing responses were inversely proportional to raw linseed oil concentrations. None of the oils significantly affected muscoid (F(4/32) = 1.6959, P = 0.1753) or tabanid (F(4,32) = 1.7546, P = 0.1624) landing response, or tsetse fly resting persistence (F(4,32) = 0.9641, P = 0.4406) on the targets.

The reduced tsetse fly response to targets treated with any of the oils can be attributed to adverse effect of the oil treatments on the tsetse fly olfactory responses to the targets. Since the oil formulations reduce target efficiency by reducing tsetse responses to the targets, application of the oil formulations on targets deployed in G. pallidipes and G. m. morsitans control programmes is not recommended.

Teneral tsetse flies, Glossina morsitans morsitans (Mall) aged less than 32 h were divided into two groups and infected initially with Trypanosoma congolense IL 1180. Flies of group A were maintained on healthy rats and those of group B fed exclusively on parasitaemic rats, to ensure regular re-infection. Flies in group A recorded mesoprocyclic, metacyclic and vectorial competence (VC) index values of 0.65 ± 0.09; 0.73 ± 0.10 and 0.47 ± 0.11, respectively. The corresponding values for group B flies were 0.76 ± 0.08; 0.79 ± 0.08 and 0.60 ± 0.10. In group A, the mesoprocyclic and the VC indexes of the females were significantly higher than those of the males. In group B, no such significant differences were registered between the sexes. For both sexes taken together, the mesoprocyclic and the VC indexes of the tsetse flies of group B were more important than those of flies of group A. Males of group B revealed a higher VC index than that of group A males; no significant differences in this index were observed in the females of both groups.

The pathogenicity of cyclically transmitted C16 clone 1 of Trypanosoma brucei metacyclics which developed within normal and hypertrophied DNA virus-infected salivary glands of Glossina morsitans morsitans was studied in the inbred, BALB/c mice. Microscopic examination of salivary glands obtained from G. m. morsitans with combined virus and T. brucei infections (i.e. the flies which transmitted the trypanosome infection to the test group of mice, group A) revealed that the glands comprised hyperplastic epithelial cells, some of which were fragmented, and numerous metacyclic trypanosomes. All the mice which contracted trypanosomiasis from G. m. morsitans with only T. brucei, i. e., the control mice (Group B; n=4) and the mice in the test group (n = 3) developed high parasitaemia and died. Repeated-measures analysis of variance using adjusted mean rate revealed that the mean prepatent periods and the mean times to death in both the control and the test groups of the BALB/c mice were not significantly different (P > 0.05). Analysis of log-transformed data fitted to a logistic growth model revealed that the rate of multiplication of T. brucei parasites in the blood of the test group BALB/c mice (r=2.373) was greater than in the control mice (r=0.808) and that the maximum carrying capacity was also attained earlier in the former group. These observations imply that the development of T. brucei metacyclics within hypertrophied salivary glands and their co-existence with the DNA virus particles might have enhanced their infectivity and virulence in the mice.

Sexual receptivity was investigated in female Ghssina morsitans morsitans Westwood after mating. The degree of insemination and duration of copulation could affect sexual receptivity when females mate with immature males. However, matings with mature males showed no effect. The “jerking phase” appears to be an important mechanical factor in female post-mating refractory behaviour.

Newly deposited Glossina morsitans morsitans larvae were chilled over ice and inoculated with 1 μ1 of either virus suspension derived from Glossina pallidipes salivary gland homogenate or sterile tsetse physiological saline. They were allowed to pupariate and then maintained at 25°C, 70% r.h. until soon after emergence when their salivary glands were examined for enlargement and presence of virus particles. Teneral G. m. morsitans which received the virus inoculum (n = 135) as larvae all became infected as revealed by gross hypertrophy of their salivary glands and ultrastructural manifestation of virus particles within the glandular epithelial cells and lumina. In the control group, which received the tsetse physiological saline (n = 91), only 1.1% of the flies showed the salivary gland enlargement, a level equivalent to the prevalence of virus infection normally detectable in the G. morsitans colony. This technique opens the way for testing the biocontrol potential of this virus. The DNA virus from G. pallidipes is clearly infective to G. morsitans morsitans, suggesting that the hypertrophied, chalky-white salivary glands, reported in various Glossina spp., are a manifestation of infection by one and the same virus.

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.

In April–May 1986, 180 male and 218 female Glossina morsitans morsitans Westwood, each less than 1 day old, were marked uniquely and released unfed on Redcliff Island, Lake Kariba, Zimbabwe. Flies were recaptured on ox fly-rounds carried out twice daily for 6 months; marks were recorded and the flies released. For females, 56% were recaptured at leastonce; the capture probability for a given 9-day period changed with age, falling from 0.32 after birth to 0.16 by 30 days and rising above 0.5 by 80 days. For males, 57% were recaptured; the probability was 0.21 for age less than 9 days, but > 0.77 for all older flies. The capture probabilities and fly-round catches were used to estimate the change with age in the daily mortality. Female mortality was 6.8% shortly after emergence, < 1% for ages 20–50 days and rose to 5% by 130 days—a pattern similar to that for laboratory reared tsetse. Male daily mortality was 8.3% after emergence, fellto 5.5% by 9 days, then rose continuously to more than 10% by 30 days. The mortality changes are related to age rather than climate. Tsetse caught on ox fly-rounds from a natural population were aged using ovarian dissection and wing-fray analysis. The age distribution (corrected using the capture probabilities from Redcliff) was consistent with the idea that, here too, mortality increased with age.

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.

Immune haemolymphs from the giant silkmoth, Hyalophora cecropia and, to a lesser extent, from the tsetse, Glossina morsitans morsitans possess antibacterial activities against several species of bacteria known to be pathogenic to man, animals and poultry, as demonstrated by in vitro bacterial growth inhibition assays. Cecropia immune haemolymph possesses a broader antibacterial spectrum and was found to be active against several Gram-positive and Gram-negative pathogenic bacteria. Mice injected with pre-determined lethal doses of Enterobacter cloacae, Klebsiella pneumoniae and Corynebacterium pseudotuberculosis and then treated with single intraperitoneal or subcutaneous injections of Cecropia immune haemolymph had much lower mortality than untreated controls. A possibility of developing a broad-spectrum antibiotic modelled on insect immune factors is discussed.

Adult survival, puparial production, weight and viability, and the sex ratio of adults emerging from puparia of Glossina morsitans morsitans Westwood maintained through four successive reproductive cycles on daily (SO), every other day (SI) and every third day (S2) feeding regimen, respectively were investigated at Chilanga, Zambia. Only in puparial production (0.8 under S0 and S1, 0.7 under S2) and puparial weight (25.1±0.2mg under S0, 24.1±0.3mg under S1, 22.5±0.3mg under S2) were significant differences (P<0.05 and <0.01 respectively) detected between feeding regimens. Nevertheless, a combination of S1 and S2 regimens is recommended for further evaluation as a more convenient and economical alternative to the S0 regimen for tsetse mass production in Africa.

The ultrastructural changes in the ejaculatory duct epithelium in Glossina morsitans morsitans Westwood was examined for special features related to spermatophore formation; special attention was paid to the cytoplasmic organelles and the plasma membrane specializations (apical infoldings and space formation). Internally, the transportation system is characterized by a cuticle-lined lumen bordered by cuboidal cells. The endoplasmic reticulum is scarce, while mitochondria are distributed throughout the cytoplasm. At the cuticular surface of the cells, extensive apical infoldings are associated with numerous mitochondria. Glycogen granules are found only in the cytoplasm of teneral flies. Apically, adjacent cells are tightly apposed; however, prominent intercellular spaces develop (1 to 7 days), permeate most of the epithelium and connect to the basal surface of the cells. These are features characteristic of transporting cells believed to have an absorptive function. As the adult fly ages, the ultrastructural characteristics of the epithelium change and are typified by the disappearance of glycogen granules and the formation of intercellular spaces. The features of the ejaculatory duct are discussed briefly in terms of their role in spermatophore formation.

The tsetse, Glossina morsitans morsitans, has two pairs of Malpighian tubules. Ultrastructurally, the tubules consist of three recognizable functional zones: the distal, intermediate and proximal regions, which are characterized by three distinct cell types: I, II and III respectively. The three cell types had numerous microvilli and basal infoldings: the microvilli of type I and II cells were associated with long mitochondria, while those of type III were devoid of mitochondria. Autoradiographic observations using (3H) glucose indicated that there was synthetic activity in the tubules, and that there was greater incorporation of the radiochemical in the distal and intermediate tubule regions than in the proximal region. The distal and intermediate regions have some functional similarities. With regard to primary urine formation in the tubules, it is suggested that the cell types I and II (and hence the distal and intermediate regions) are secretory, and the cell type III (that is, the proximal region) is absorptive. “Canaliculi” in the proximal region increase the surface area for absorption.

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.

Haemocoelic injections of live Escherichia coli and oral administration of three tetracycline compounds, namely Reverin, Maxitet and Terramycin to female Glossina morsilans morsitans prior to their first larviposition, caused a decrease in fecundity, but had no effect on longevity. Trypanosoma brucei brucei and T. congolense administered by haemocoelic injections, however, caused no change in fecundity or longevity, but tsetse infected with T. b. brucei and T. congolense in their mouthparts had decreased fecundity and longevity as compared to controls.

The anterior aorta is rich in axons and axonal endings originating from the nervus corporis cardiacum (NCC) and the corpus cardiacum (CC). Neurosecretory granules in the NCC axons are small compared to large granules synthesized in the CC. Vesiculation of the secretory granules into clusters of small vesicles occur both in NCC axonal endings and axon-like processes from the CC, suggesting that both types of secretions are released into the haemolymph.

Synapses occur between the NCC axons and cardiac muscle cells, as well as with cell processes from the CC, suggesting that some of the neurohormes from the NCC axons may function as neurotransmitters. The CC consists of large neuron-like cells, that synthesize an intrinsic secretion; it also contains a neuropil of NCC axons and CC cell processes. There is no evidence of a separate storage and release lobe in the CC. No synapses occur between the axons and cell processes or with the cell bodies. The CC cell processes have their endings in the aortic wall where they make synapses with NCC axonal endings and where they most likely release their material. It is suggested that in Glossina: (a) the aortic wall has taken over the neurohaemal role of the CC whose function otherwise remains that of synthesizing an intrinsic hormone; and that (b) the activity of the CC to synthesize and/or release its intrinsic secretion is most likely controlled in the aortic wall via a neurotransmitter substance.

Recording of electroantennographic (EAG) responses from tsetse, Glossina pallidipes and G. morsitans morsitans (Diptera: Glossinidae) has been used to detect olfactory stimulants in volatiles from cattle. The most potent stimulant in cattle odours collected on Porapak resin has been identifiedas 1-octen-3-ol by gas chromatographic retention data and mass spectrometry. The rate of production of 1-octen-3-ol by a normal ox was estimated to be 0.043 mghr−1, and the natural material was shown to be predominantly the (R)-(−)enantiomer. No 1-octen-3-ol was collected under the conditions used in the absence of an ox. EAG dose-response curves to 1-octen-3-ol showed it to be about 106 times more potent than acetone, a known attractant for tsetse, with the maximum response of about 1 mV occurring to approx. 1 ng at source. 1-octen-3-ol caused increased upwind flight by tsetse in a wind tunnel bioassay, and in the field it was attractive to tsetse by itself and also increased the attractiveness of both ox odour and of mixtures ofcarbon dioxide and acetone.

A significant increase in mortality was observed in Glossina morsitans morsitans maintained for approx. 45 days on rabbits immunized with tsetse or bovinetrypsin. Tsetse and bovine trypsin were observed to cross-react when tested with an immunodiffusion technique. A significant decrease in fecundity was observed in flies fed on bovine trypsin-immunized rabbits. Pupae collected from flies maintained on rabbits immunized with tsetse and bovine trypsin were significantly lighter. A significant number of flies maintained on rabbit immunized with thoracic muscles, gut bacteria and bovine trypsin had permanently laterally extended wings.