Glossina austeni (Diptera : Glossinidae) eradicated on the Island of Unguja, Zanzibar, using the sterile insect technique

An area-wide integrated tsetse eradication project was initiated in Zanziba r in 1994 by the International Atomic Energy Agency and the governments of Tanzania and Zanzibar, to eradicate Glossina austeni Newstead from Unguja I sland (Zanzibar) using the sterile insect technique. Suppression of the tse tse population on Unguja was initiated in 1988 by applying residual pyrethr oids as a pour-on formulation to livestock and by the deployment of insecti cide impregnated screens in some of the forested areas. This was followed b y sequential releases of gamma-sterilized male flies by light aircraft. The flies, packaged in carton release containers, were dispersed twice a week along specific night lines separated by a distance of 1-2 km. More than 8.5 million sterile male flies were released by air from August 1994 to Decemb er 1997. A sterile to indigenous male ratio of >50:1 was obtained in mid-19 95 and it increased to >100:1 by the end of 1995. As a consequence the prop ortion of sampled. young females (1-2 ovulations), with an egg in utero in embryonic arrest or an uterus empty as a result of expulsion of a dead embr yo, increased from <25% in the Ist quarter to >70% in the last quarter of 1 995. In addition, the age structure of the female population became signifi cantly distorted in favor of old flies (greater than or equal to 4 ovulatio ns) by the end of 1995. The apparent density of the indigenous ny populatio n declined rapidly in the last quarter of 1995, followed by a population cr ash in the beginning of 1996. The last trapped indigenous male and female f lies were found in weeks 32 and. 36, 1996, respectively. Time for 6 fly gen erations elapsed between the last catch of an indigenous fly and the end of the sterile male releases in December 1997.