The first step in the eradication of the fly is to determine its habitat. Measures have long been in force to combat the fly in both the Rhodesias, but today as a direct result of the building of the Kariba Dam and the consequent resettlement Kariba, to new homes higher up, a whole new area is being opened up and cleared of fly. One of my early journeys was undertaken on a fly survey in the Gwembe Valley. I set off accordingly in a Land-Rover with one of the two tsetse supervisors in the area, a trailer carrying our gear and camping equipment for a week, an African tsetse guard, a hunter attached to the Control Department and a couple of labourers to act as carriers and help in setting up camp.
A course was plotted throughout the area and each morning we went out on foot, accompanied by a local villager who acted as our guide. We averaged about seventeen miles a day, stopping every two hundred yards or so beside a large tree. Here we lined up, the sun beating down and reflected off the hard-beaten earth, while Saul, the tsetse guard, solemnly inspected our backs, butterfly net at the ready, to catch any fly that might have landed on us. There we would stand, looking slightly ridiculous and, as I sometimes reflected rather grimly, mutely offering ourselves up as a human sacrifice in the cause of progress. Hungry flies tend to settle head up on the catchers; the less hungry ones head down. Having caught your tsetse, the next step is to verify the species, determine its sex and whether it has fed.
The tree under which we have been standing, thankful of its temporary shade, is then marked. One of the labourers, whose responsibility this is, cuts a square of bark out of the trunk and, if fly is present in the area, paints the bare patch red. Meanwhile the tsetse supervisor notes the kind of tree, the presence of game, already detected by the keen eyes of the hunter always
on the look-out for spoor, and wind and weather conditions. The history of the district in relation to tsetse population must be studied along with some account of the rainfall, temperature and the number of flies caught. The survey is usually summed up in a map of the area, showing the topographical details, the distribution of vegetation and the fly distribution as far as it is known. Later, tsetse lines will be cut through the bush and traversed regularly by African staff and a day-to-day record is kept throughout the year.
Glossina morsitans are found in almost any wooded area other than the very dense thickets, so it is possible to rule out large tracts of country as being unsuitable. Their natural reaction is to seek places of higher light intensity which brings them out into open glades or other spots frequented by animals, especially the junctions of paths about water-holes, stamping grounds of game and so forth. There, from the vantage-point of the underside of branches about ten feet off the ground, they can probably see game passing up to a distance of 200 yards.
The flies’ resting ground is first removed by selective clearing of trees so that it is no longer cool enough for them and the hot season usually kills them off. Intensive ‘fogging’ with thermal aerosol insecticide follows, which acts at once and clears effectively any fly lingering in the vicinity. This is an expensive operation, costing roughly £150 a square mile, as four applications are needed at 21-day intervals, corresponding with the hatching periods of the fly.
Several natural factors fortunately combine to limit the fly and help in the fight to exterminate it. The pupae for instance are attacked by various parasites and ants eat them, so that from one cause or another, including drowning and baking, probably only half survive to become flies. The flies in their turn have their own predators in birds, wasps, jumping spiders and probably lizards.
It must be stressed that all operations are aimed at the protection of the African and the control of tryps. To this end, treatment with trypanocidal drugs is being used on African cattle where they are subject to the tsetse fly challenge. Well over 200,000 doses of trypanocidal drugs are yearly used by the Veterinary Department on cattle in Northern Rhodesia, at a cost of approximately £12,500, while the yearly expenditure of the Tsetse Department on fly control measures amounts to a further £160,000.
Once it has been decided that an area is clear enough to allow cattle to be kept, the Veterinary Officer is notified. A simple kraal is erected, opening into a narrow pen through which the cattle pass for inoculation. From time to time blood smears are taken and examined under a field microscope. A wet smear will show any tryps present in the bloodstream, while a dry smear allows identification of the kind of trypanosome. Injections are carried out in fly areas every two months and all cattle in marginal areas are examined once a month. As a result, infection has dropped and herds have increased. At Nyangwena, east of Lusaka, I saw cattle in the first stages of the disease, the trypanosomiasis being arrested by regular inoculation; beside them were magnificent animals, fully recovered, that once might have wasted miserably away.