A wide range of objects have been designed to attract tsetse, such as simple cloth screens, or to both attract and catch them, traps of varying degrees of complexity. The shape and size of these objects affect the number of flies that are attracted to their vicinity and those that actually alight on them or, in the case of traps, are caught by them. Studies on the spectral responses of male Glossina morsitans morsitans, using electrophysiological and behavioural techniques, have shown response maxima in the u.v. and in areas of the visible range. Preliminary field studies are described, in which performances of traps covered in different coloured materials of known spectral reflectance were assessed. The most important colour determinant of trap score is the proportion of attractive blue (400–500 nm) to unattractive green-yellow (500–600 nm) in the reflectance of the material used. Reflectivity of red (above 600 nm) is also a positive factor in trap attractiveness. Optimising the visual attractiveness of targets is particularly important if odour is not employed to effect the initial attraction of tsetse to their vicinity.

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.

Studies on G. m. morsitans clearly indicate that the foundations for acoustic communication among tsetse exist. Tsetse produce sound in connection with the important physiological activities of feeding, mating and larviposition. The possible role of these acoustic emissions in the complex behaviour patterns of tsetse is discussed.

Upwind flight has been elicited in tsetse, Glossina morsitans exposed to host odour and to active components of host odour (carbon dioxide, acetone and 1-octen-3-ol) in a wind tunnel. With the exception of octenol the odours also produce marked kinetic effects in G. morsitans, G. austeni, G. pallidipes and G. palpalis. Threshold concentrations for G. morsitans are in the region of 0.2% for ox odour, 0.01% for carbon dioxide and 400 μgl−1 for acetone.

The importance of maximum rates of insemination in female tsetse is emphasized in relation to their low rate of reproduction and to the possibility that density dependent regulation of tsetse populations may not be as rigorous as in many oviparous insects. Observations on the mating behaviour of tsetse are described and its regulation by sex pheromones which serve to identify females of the species is discussed. Laboratory and field experiments have shown that the sexual activity of G. m. morsitans males can be manipulated by presentation of synthetic sex pheromone on suitable decoys in the laboratory and in the field. Males that respond to decoys in the field are in the same nutritional state as others which are attracted to the models upon which the decoys are placed and are presumably seeking food. There is no reason to believe that sexual activity is restricted to a particular section of the population, and given a choice, it is proposed that mating is preferable to feeding in terms of gene survival for the individual male. The durations of copulatory responses are dose dependent and there is some evidence that they are inversely proportional to the frequency of encounters with decoys and hence to the density of flies. Techniques for the reduction of tsetse populations using sex pheromones in conjunction with suitable decoys and chemosterilants are being developed. The availability of pheromones in large quantities will permit their testing as sexual confusants among males and may lead to interspecific matings where more than one species occupies the same habitat.

Biconical traps were studied for their efficiency in sampling for Glossina morsitans morsitans Westw., G. pallidipes Aust., G. austeni Newst. and G. brevipalpis Newst. in three localities in Mozambique where these species occur sympatrically or singly. Studies were also carried out to determine whether acetone vapour was effective in enhancing the efficiency of the biconical trap. Various comparisons were also made between biconical traps and Langridge traps, and with fly-round patrols, with and without bait oxen.

It was demonstrated initially that the blue biconical trap (BBT) was more efficient for G. morsitans and G. pallidipes than red or white models or Langridge traps. In all subsequent studies, therefore, the BBT was used. It was concluded that: the BBT was ineffective for sampling G. morsitans, with or without acetone; the BBT was markedly more effective than fly rounds for sampling G. pallidipes, and its efficiency was significantly enhanced by acetone; and G. austeni was attracted to the BBT, but not all flies would enter the non-return cage—G. brevipalpis was readily caught in the BBT. Acetone with the BBT gave inconclusive results for these species.

Although biconical traps are now widely used for the sampling of tsetse populations, they provide only relative population estimates determined by the fly density, activity and trap response. Studies were therefore undertaken to convert such biconical trap indices into unbiased absolute population density estimates. The first step was to determine the range of attraction of such traps for the main trypanosome vector in Kenya, Glossina pallidipes, although some data were also obtained for G. brevipalpis. Two different techniques were used. Firstly traps were placed at varying distances apart, resulting in competition and consequent reduction of catch sizes per trap when ranges of attraction overlapped. Secondly, the catches in grassland at varying distances from a forest edge were compared with two predicted functions relating catch size to distance. Results from the competition experiments showed a marked decline in catch per trap when the intertrap distance was less than 30–40 m. The resultant estimate of maximum range of attraction of 15–20 m for G. pallidipes was compatible with the observed pattern of decline of catches at increasing distances from the forest edge. The range for G. brevipalpis was tentatively estimated as up to 10–15 m.

A method is suggested for estimating sampling biases for male tsetse, based on the assumptions of the classical feeding cycle “model”. Sampling intensity for any particular method is denned as the catch of flies in different segments of the non-feeding phase of their current cycles, expressed as a percentage of the catch of flies that are just entering the feeding phase. Two examples are given, of Glossina palpalis in Nigeria and G. morsitans in Zambia. In both cases, sampling intensity is low just after feeding and increases slowly at first, and then rapidly as flies enter the feeding phase.

Flies in their feeding phase can apparently find and feed on hosts within one day. Feeding rates are inversely related to the fat content of flies entering the feeding phase of their current cycle, whilst rates of fat usage increase with this variable. These results suggest that it is important to distinguish between tsetse flight activity in general, and feeding behaviour in particular. Finally, it is emphasised that the analytical technique proposed depends on our still inadequate understanding of the field behaviour of flies.

A study of Glossina pallidipes (Austen) was done using various trapping devices. It was observed that groups of females of the same physiological age, the same pregnancy stage, and all replete, entered traps simultaneously. Swarms of teneral females of the same physiological age were also captured simultaneously. These observations led to the conclusion that female tsetse swarm together according to pregnancy stage and/or age groups for the purpose of both looking for hosts and larviposition sites. Laboratory studies on the feeding pattern and behaviour of heavily pregnant female G. pallidipes indicated that only about 5% of such females fed 2 days before larviposition; that is when the breathing lobes of the larva had turned black and it was ready to be larviposited. The rest did not take a meal once they were in the last stage of pregnancy. Field observations of fed females in similar pregnancy stage generally agreed with this, indicating 4.6% as the portion that fed when in that last pregnancy stage. The abortion rate in the field population was estimated to be about 0.1%. The weakness of the method of determining abortion rates in the field is discussed.

Trypanosomiasis outbreaks of great severity, both medical and veterinary, still occur. At the present time some of these outbreaks can be contained by implementation of plans based on sound knowledge of tsetse distribution. However, for many countries such knowledge is fragmentary. For this reason the second edition of tsetse distribution maps is to be regarded as provisional only, pending the availability of more accurate data. Some of the new information that has been received since 1973 is reported. It is concluded that a programme of intensive revision is needed before it can be claimed that tsetse situation in Africa is well understood.

A year round ecological study of Glossina morsitans submorsitans variety ugandensis was carried out from September 1980 to August 1981 in the Finchaa river valley in the western part of Ethiopia. Two sampling methods, namely vehicle patrol and screen/handnet capture were employed. The latter was more efficient. The effect of various environmental factors (e.g. altitude, climate, vegetation etc.) that determine the eco-distribution of this species of tsetse were analysed. The most significant finding was that tsetse were distributed far above the previously known altitude limits.

Population regulation is briefly explained, and the demographic parameter, r, is identified as a symptom of the dynamic balance between density-independent and density-dependent factors that respectively disturb or regulate population equilibria. Evidence for density-dependence in tsetse populations is reviewed under the general headings of direct and indirect observations. Direct evidence comes from predation experiments on both adults and puparia, and from experiments that measure the feeding success of tsetse on bait animals. Indirect evidence arises from detailed analyses of fly-round records. Natural density-dependence in tsetse populations, when it occurs, is shown to be considerable, and must always be allowed for in control programmes whose effectiveness it at least partly determines.

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.

The infection rates and transmission characteristics of sterile male Glossina morsitans centralis, G. austeni and G. tachinoides for Trypanosoma vivax, T. congolense and T. brucei were studied. Teneral males were irradiated with 10 krad in a 137caesium source under ambient conditions. Five groups of teneral males of each species were sterilised by irradiation with 10 krad caesium source under ambient conditions and then fed for 3 days, together with five groups of normal males of their respective species, on three goats infected with T. vivax, T. congolense or T. brucei. The mean sterility rates were 98, 93 and 90% for G. m. cenlralis, G. austeni and G. tachinoides respectively. The mean percentage mature infection rates in the irradiated as against the controls of G. m. centralis, G. austeni and G. tachinoides were respectively 27.3 ± 9.5/27.7 ± 11.1, 4.0 ± 1.4/4.0 ± 2.6 and 14.8 ± 7.0/12.2 ± 5.0 for T. vivax; 24.6 ± 5.2/30.3 ± 4.3, 0.7/0.3 and 0.3/0.3 for T. congolense; and, 22.7 ± 2.6/23.4 ± 3.1, 1.1/0.2 and 0.7/1.7 for T. brucei. The transmission rates and frequency to A/J mice were very high and did not differ between the sterile and normal males. There was also no difference in the pattern of the diseases in the goats challenged by sterile or sexually fertile males of the three tsetse species. These results indicate that releases of sterile male tsetse in tsetse control programmes will potentially increase the trypanosomiasis risk in the affected area. Hence appropriate measures should be integrated in any SIR method of tsetse control campaign in order to provide adequate protection to man and his associated livestock.

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.

The paper presents a way of estimating average daily mortality rates of female tsetse from ovarian age distributions. This technique was applied to monthly biconical trap samples of G. palpalis taken during and after insecticidal campaigns in the Bouaflé region of Ivory Coast. A clear inverse relationship is demonstrated between the annual mean number of females per trap per sample at 10 separate sites, and the mean annual mortality rates calculated for them. Local variation in the impact of insecticides is explained in terms of the grouping of the sites either side of a level of natural mortality above which tsetse populations cannot be sustained through reproduction alone.

A theoretical model for density dependent population growth is presented and applied to a particular control situation, that of the sterile insect release method. The model demonstrates that the effectiveness of any particular level of induced sterility (or mortality) is crucially determined by the natural resilience of the target population.

In 1981 an attempt was made to eradicate a 300 km2 fly-belt of Glossina pallidipes (Austen) in the Lambwe Valley of western Kenya by means, principally, of sequential aerial application of endosulfan aerosol spray. The progress of spraying operations was monitored entomologically by surveying for fly with biconical traps sited in main habitats of thicket, Acacia woodland and coniferous plantation, and by age-grading females caught between spray cycles.

Although nine spray applications of relatively heavy dosages of insecticide were carried out, the campaign ultimately failed to accomplish its objective. Females which had clearly survived and bred in the intervals between spray cycles were found throughout the area. By the end of operations, the tsetse population appeared to have been reduced by 99.9% in thicket and woodland, and by 99% in coniferous plantation. Nevertheless, on the basis of a crude estimate of total fly numbers in the Lambwe Valley, several thousand flies possibly remained after spraying.

Monthly post-spray monitoring showed that the population in thicket fully recovered in about 12 months, but to only 20–30% of its original level in woodland and plantation two years after spraying. The population in thicket maintained an approximate equilibrium density after recovery, indicating that density-dependent processes had re-established a regulatory effect. There was some evidence that this was brought about in part by fly movement. Calculations of the population growth rate gave a value for r, the instantaneous rate of increase, of 0.015 per day; equivalent to a finite rate of increase of 1.610 per month, and a population doubling time of 45 days. Some possible ecological reasons for failure to achieve eradication are discussed.

The effects of gamma irradiation from a 60Co-source on Glossina palpalis palpalis (Robineau-Desvoidy) were established in laboratory tests. Dose-response data indicated that fecundity was reduced by about 95% following exposure of late stage puparia or young adults to 11–13 krad in air and 15–18 krad in a nitrogen atmosphere. None of the treatments had a detectable influence on the viability, mating behaviour, inseminating capability or competitiveness of the adult males.

When irradiated males were combined in varying ratios with untreated males and females, increasing numbers of sterile males resulted in a considerable reduction in pregnancy stages beyond the egg stage, an increasing proportion of parous females with an empty uterus due to expulsion of a dead embryo after embryonic arrest or due to ovary blockage and an increasing percentage of females with a degenerating egg in utero.

Remating of inseminated females with fertile males during the period when most of them had emptied their uterus (day 14–20) after embryonic arrest, had no noticeable effect on the sterility rate.

A most important consequence of recurring embryonic death was a detectable imbalance between intra-uterine and ovarian development. Some aberrations can be used as additional criteria for monitoring the effectiveness of sterile males released in the field.

Females irradiated in the pupal or adult stage displayed a normal receptivity and insemination rate and survived distinctly longer than untreated controls. Moreover, they built up abnormally abundant fat bodies and showed multiple mating scars (restricted to the palpalis group species) and completely atrophied ovaries.

It is postulated that the release-recapture and examination of the reproductive tract of irradiated females during an advanced stage of sterile release vector control operations would give evidence of mating that could expose the existence of relic wild populations, particularly when the natural tsetse population has been reduced to, levels below the threshold detectable by conventional techniques.

The combination of a trapping system of insecticide impregnated screens and biconical traps followed by the release of sterile males led to the complete control of Glossina palpalis gambiensis and Glossina tachinoides in the agro-pastoral zone of Sideradougou. This area, situated south of Bobo Dioulasso, Upper Volta, in the Guinea savannah, covers an area of approx. 3000 km2. Along more than 650 km of rivers, bordered by gallery forests and infested by riverine tsetse, 6500 impregnated screens were placed during 4 months of the dry season, followed by the release of sterile males in the rainy season. For release purposes, colonies of 150,000 producing females of G.p. gambiensis and 85,000 females of G. tachinoides were maintained in industrial colonies on artificial membranes. Reinvasion of the project area was prevented by two barriers consisting of biconical traps impregnated with synthetic pyrethroid in one and simple biconical capture traps in the other. The screens reduced the initial fly population by 94% and permitted the release of only 35 sterile males per km of river to attain the planned ratio of seven sterile males to one wild male. Regular surveys showed that, after 4 months of release of sterile males, the relic fly population was constantly decreasing and tending towards disappearance.

An economic evaluation based on the production costs of the sterile males together with the costs of field operations showed that this combination of two non-pollutant methods was competitive with other methods of tsetse control.