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.