In Rhodesia, field studies were made of the initial attraction of G. morsitans morsitans Westw. and G. pallidipes Aust. to mobile and stationary baits, using flight traps which surrounded baits or which were placed in the densest part of the attracted swarm. With stationary baits, many flies were attracted by host odour and visual stimuli assisted final orientation. With mobile baits, many flies were attracted by visual stimuli alone; odour did not increase attraction. With both mobile and stationary baits, there was no indication that major hosts are much more effective than minor ones as initial attractants, although stationary men were exceptionally poor baits, for G. pallidipes especially. The sex and species compositions of catches from stationary baits other than men were representative roughly of the inactive population-70% females of both species, and a roughly 1:4 ratio of G. morsitans to G. pallidipes. The sex and species compositions of catches from all mobile baits were biased-40% female G. morsitans, 60% female G. pallidipes, and a roughly 2:1 species ratio. Nearly all flies attracted to stationary baits were hungry whereas 10-25% of both sexes visiting mobile baits had fed recently. The use of a variety of electrocuting devices showed that compact persistent responses and alighting reactions of attracted flies were evident more for males than for females, more for G. morsitans than for G. pallidipes, more near model animals with host odour than near odourless models, more near models than near men, and more with tenerals and hungry non-tenerals than with recently fed flies. Men with mobile baits depressed greatly the alighting reactions and with stationary baits men inhibited greatly the initial attractions. Both effects of men were greater with females than with males and greater with G. pallidipes than with G. morsitans. Men were recognised by their upright appearance and odour. Only desperately hungry flies probed men whereas less-hungry flies probed an ox with men. Food-seeking flies of differing nutritional state were not shown to distinguish between mobile and stationary baits. Although the results support the conventional view that mating and feeding functions in the response to hosts occupy distinct phases of the hunger cycle, •it seems necessary to modify the conventional view by placing more emphasis on the role of mobile baits as food sources and by envisaging a definite mate-seeking response by mature females.

BackgroundGambian sleeping sickness (human African trypanosomiasis, HAT) outbreaks are brought under control by case detection and treatment although it is recognised that this typically only reaches about 75% of the population. Vector control is capable of completely interrupting HAT transmission but is not used because it is considered too expensive and difficult to organise in resource-poor settings. We conducted a full scale field trial of a refined vector control technology to determine its utility in control of Gambian HAT.Methods and FindingsThe major vector of Gambian HAT is the tsetse fly Glossina fuscipes which lives in the humid zone immediately adjacent to water bodies. From a series of preliminary trials we determined the number of tiny targets required to reduce G. fuscipes populations by more than 90%. Using these data for model calibration we predicted we needed a target density of 20 per linear km of river in riverine savannah to achieve >90% tsetse control. We then carried out a full scale, 500 km2 field trial covering two HAT foci in Northern Uganda to determine the efficacy of tiny targets (overall target density 5.7/km2). In 12 months, tsetse populations declined by more than 90%. As a guide we used a published HAT transmission model and calculated that a 72% reduction in tsetse population is required to stop transmission in those settings.InterpretationThe Ugandan census suggests population density in the HAT foci is approximately 500 per km2. The estimated cost for a single round of active case detection (excluding treatment), covering 80% of the population, is US$433,333 (WHO figures). One year of vector control organised within the country, which can completely stop HAT transmission, would cost US$42,700. The case for adding this method of vector control to case detection and treatment is strong. We outline how such a component could be organised.

Field studies with Glossina morsitans morsitans Westw. in Rhodesia showed that hand-net catches can reduce slightly the responses of males to mobile baits and can reduce female responses by three-quarters. Description is given of methods of operating baits in the absence of men and of methods of electrocuting flies as they fly near baits, alight on baits and respond to decoy tsetse. These techniques are more efficient and objective than hand-net catching.

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 identified as 1-octen-3-ol by gas chromatographic retention data and mass spectrometry. The rate of production of l-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 (/?)-( -)enantiomer. No l-octen-3-ol was collected under the conditions used in the absence of an ox. EAG dose-response curves to l-octen-3-ol showed it to be about 10 6 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. l-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 of carbon dioxide and acetone.Resume-Les reponses electroantennographique (EAG) des mouches tse-tse, Glossina pallidipes et G. morsitans morsitans (Diptera: Glossinidae), ont ete notees afin de decouvrir les stimulants olfactifs parmi les composes volatils emanant du betail. Le stimulant le plus puissant dans l'odeur de betail, recueillie sur la resine Porapak, a ete identifie comme l-octen-3-ol en utilisant des donnees de retention chromatographique en phase gazeuse et spectrometrie de mass. On a estime le taux de production de l-octen-3-ol par un boeuf normal a 0,043 mghr" 1 et la matiere naturelle s'est revelee comme composee en majeure partie de l'enantiomere (R)- (-). Dans les conditions utilisees, on n'a recueillie de l-octen-3-ol qu'en presence d'un boeuf. Les courbes de dosage-reponse EAG pour l-octen-3-ol l'a revele a peu pres 10 6 fois plus puissant que l'acetone, un attractant connu pour les mouches tse-tse, la reponse maximum d'environ 1 mV etant enregistree pour environ 1 ng a la source. l-Octen-3-ol a occasionne un accroissement de vol des mouches tse-tse contre le vent dans un tunnel aerodynamique. Sur le terrain l-octen-3-ol s'est reveje attractif tout seul et a augmente la puissance attractive de l'odeur de boeuf et aussi des melanges de bioxyde de carbone et d'acetone.

BackgroundMost cases of human African trypanosomiasis (HAT) start with a bite from one of the subspecies of Glossina fuscipes. Tsetse use a range of olfactory and visual stimuli to locate their hosts and this response can be exploited to lure tsetse to insecticide-treated targets thereby reducing transmission. To provide a rational basis for cost-effective designs of target, we undertook studies to identify the optimal target colour.Methodology/Principal FindingsOn the Chamaunga islands of Lake Victoria , Kenya, studies were made of the numbers of G. fuscipes fuscipes attracted to targets consisting of a panel (25 cm square) of various coloured fabrics flanked by a panel (also 25 cm square) of fine black netting. Both panels were covered with an electrocuting grid to catch tsetse as they contacted the target. The reflectances of the 37 different-coloured cloth panels utilised in the study were measured spectrophotometrically. Catch was positively correlated with percentage reflectance at the blue (460 nm) wavelength and negatively correlated with reflectance at UV (360 nm) and green (520 nm) wavelengths. The best target was subjectively blue, with percentage reflectances of 3%, 29%, and 20% at 360 nm, 460 nm and 520 nm respectively. The worst target was also, subjectively, blue, but with high reflectances at UV (35% reflectance at 360 nm) wavelengths as well as blue (36% reflectance at 460 nm); the best low UV-reflecting blue caught 3× more tsetse than the high UV-reflecting blue.Conclusions/SignificanceInsecticide-treated targets to control G. f. fuscipes should be blue with low reflectance in both the UV and green bands of the spectrum. Targets that are subjectively blue will perform poorly if they also reflect UV strongly. The selection of fabrics for targets should be guided by spectral analysis of the cloth across both the spectrum visible to humans and the UV region.