Further eradication of tsetse in the Chad and Gongola River systems in north-eastern Nigeria.
The following is substantially the author's summary. During the years 1963-70, further progress was made in eradicating tsetse flies (Glossina tachinoides Westw., G. morsitans Westw. and G. palpalis (R.-D.)) from parts of north-eastern Nigeria, by using a persistent insecticide (DDT or dieldrin) on resting sites as previously described [RAE B 53 239] and further modifications were made in the spraying technique. Where fringing forests are very wide and the river banks are indistinct, spraying is limited to strips of vegetation 20 yd wide along the outer edge of the forest and similar strips at right angles to these at intervals of about 50 yd, extending towards the moist ground along the water course. In the extensive areas of thicket on flood plains, narrow paths are cut at intervals of about 20 yd, and only the sides of the paths and the outside perimeter of the thicket are sprayed. In the more frequently encountered fringing forests bordering well defined river banks, the width of the vegetation strips sprayed along the banks has been reduced from 30 to 10 yd for G. morsitans and to 5 yd for G. tachinoides. Cessation of spraying for 24 h after showers and an increase in insecticide strength (from 2 1/2 to 5% actual DDT) and spraying height (from 2 to 5 ft) eliminated flies in the early rains. Insecticide barriers of 5% DDT over a strip up to 1 mile wide have been successful in protecting sprayed areas from reinfestation between spraying seasons. Cleared barriers averaging 2 1/2 miles wide have, so far, succeeded in providing permanent protection to completed projects. Periodical checks indicate that all the country reclaimed is free from Glossina. A total of 16 644 mile2 of tsetse-infested country has been reclaimed, making 26 540 mile2 safe for grazing. Annual costs varied, but in typical country, actual spraying expenditure averaged £N20/mile2. An overall figure of £N30/mile2 is believed to be fairly accurate.