Second Report of the Tsetse-fly Investigation in the Northern Provinces of Nigeria

Extract

This report contains a record of the trypanosome infections, food and breeding of G. morsitans and G. tachinoides obtained by examining the flies at various foci over a period of fourteen months.

It confirms the fact that the breeding of both species is practically confined to the dry season and follows a period of increased food supply. G. tachinoides is well fed through the rains, except in one month of flood, and starts breeding as soon as the rains cease, owing to its habit of feeding on reptiles. G. morsitans starts free breeding about six weeks later, as its increased food supply is due to the ungulates becoming more available.

G. morsitans does not feed on reptiles, but in times of hunger draws a proportion of its food from birds, the largest proportion recorded being 17 per cent, in one month at one focus. It draws the bulk of its food in this locality from small antelope, large game being scarce. G. tachinoides is much less specialised in its diet, and in the wet season nearly one-fifth of its food was drawn from a group of animals which included man, monkey and dog.

The infection of the flies with T. vivax and T. congolense bears a close relation to the amount of blood obtained from antelope, and consequently morsitans is in general nearly four times as heavily infected as tachinoides. Infections with T. brucei and T. gambiense are scarce in this locality. Trypanosome infection rises just before the main breeding season in morsitans in all localities and in tachinoides in places where the fly is largely a mammal feeder. The proportional infection in general falls in the season of most rapid breeding, owing to masking of the actual rise by the number of young flies examined. It rises rapidly when breeding ceases. The total infection is reduced when fly food is hard to obtain, in the time of long grass and flood, owing to T. vivax infections dying out when the flies are starved.

It is shown that in some cases T. grayi may be obtained by tachinoides when it feeds on Varanus, and a somewhat similar infection in the laboratory may be obtained by feeding the flies on toads.

It is shown that in some cases T. grayi may be obtained by tachinoides when it feeds on Varanus, and a somewhat similar infection in the laboratory may be obtained by feeding the flies on toads.

There is just an indication that postponement of grass burning may interfere with the free breeding of morsitans and in some cases that of tachinoides. This possibility is to be tested.

The experiment of excluding game and pig from one of the dry season foci of the flies by means of fencing will be carried out.