Published online by Cambridge University Press: 10 July 2009
Two experiments on factors affecting the size and composition of catches of tsetse flies, principally Glossina pallidipes Aust., were carried out in 1963 in South Busoga, Uganda. Eight attractants were distributed between eight sites on eight successive days in a Latin square design for each experiment. The attractants comprised two black Zebu oxen and Morris traps covered with ordinary hessian (brown traps) or with hessian dyed black (black traps). Three of the sites were on the edge of a large thicket, two were close to isolated clumps of thicket in the midst of grassland and three were in the open grassland itself. Catching took place for 12 hours each day. The total numbers and sex ratio were recorded for each catch, and also, from dissections, the age composition and pregnancy states of the female portion of the catch. Examples of G. brevipalpis Newst., G. palpalis fuscipes Newst. and of 13 species of Tabanidae were also caught, but in smaller numbers, and were recorded in less detail.
Catches of G. pallidipes at sites close to the thicket edge were considerably greater than at sites away from the thicket, but, apart from an increased proportion of nulliparous females at the clump and grass sites, the composition of the female sample was unaffected by the type of site. The bait-oxen caught larger samples than the traps, but a smaller proportion of females, and these contained a higher proportion of young flies and of flies carrying an egg in the uterus. In comparison with brown traps, black traps caught smaller numbers of G. pallidipes, and a smaller portion of females, but a larger proportion of these were nulliparous. Although the two oxen had been selected for similarity of size and colour, they differed in the samples they attracted: one of them consistently attracted a larger sample of all the common species and, in the second experiment, a larger proportion of females in the samples of G. pallidipes. Most examples of G. palpalis fuscipes were caught at the three edge sites, and all but one example of G. brevipalpis were caught on the bait-oxen.
All examples of the 13 species of Tabanidae caught on the oxen or in the traps were females. Apart from Tabanus par Wlk. they were poorly represented in the trap-catches, and there was no obvious effect of site upon the size of the samples.