DISTRIBUTION AND TRYPANOSOME INFECTION RATES OF GLOSSINA MORSITANS SUBMORSITANS NEWST ALONG A TRADE CATTLE ROUTE IN SOUTH-WESTERN NIGERIA

The distribution and trypanosome infection rates of Glossina morsitans submorsitans Newst. were studied during the wet season of 1967 along 75 miles of the main trade cattle route which passes through the savannah country between Ilorin and Oyo in south-western Nigeria. G.m. submorsitans was found inhabiting open woodland, grassland, farmland and the environs of towns associated with the cattle route. In comparison with the types of habitat this species occupies in its zone of wide distribution in northern Nigeria, those habitats studied were considered atypical. It is suggested that the presence of G.m. submorsitans in the area investigated had resulted from a southward population advance over the last 50 years and this hypothesis is discussed in relation to existing knowledge of G.m. submorsitans advances. The trypanosome infection rates of 61.6 and 76.6 per cent, found in 364 examples of G.m. submorsitans dissected are much higher than previously recorded for any of the subspecies of G. morsitans Westw. A steady southward increase in the trypanosome infection rates of G.m. submorsitans was demonstrated for populations inhabiting 200 miles of cattle route. Trypanosome infections in G.m. submorsitans are attributed to Trypanosoma vivax and T. congolense, and the absence of brucei-group infections is discussed in relation to the incidence of T. brucei infections in trade cattle and limitations of the technique used for demonstrating infections in tsetse flies. It is stressed that epizootiological aspects of the present findings cannot be clarified until reliable data on trypanosome infections of trade cattle in the area studied are available. © 1969, Cambridge University Press. All rights reserved.