Abstract
In transmission expts. with T. rhodesiense and G. morsitans the proportion of infected [male][male] was greater than the [female][female] by >2:1, either from flies which emerged from normal unincu-bated pupae to those from pupae incubated at 30[degree]C. In laboratory reared flies there was a higher death-rate in 9 than in c? flies. The mortality rate in the [male] flies was primarily responsible for the disparity found in the infection rate in the 2 sexes of G. morsitans in the expts.