Tanzania has the largest tsetse mass-rearing facility in Africa and the largest tsetse colony of over 600,000 female flies – the largest in the world, according to Director General of the International Atomic Energy Agency, Dr. Hans Blix, quoted in the Daily News. Although tsetse flies were a menace to the health of people and livestock, he said, still there was a need to reproduce them en masse. The flies are reared at the Tanga-based Tsetse and Trypanosomiasis Research Institute and the male flies are made sterile using gamma radiation from cobalt 60 or caesium 137 sources before their release in tsetse affected areas. Tanzania was said to be in a leadership position and could soon begin exporting flies which would help to decimate tsetse populations in other countries. Dr. Blix inaugurated a third insect rearing facility at Tanga during his visit to Tanzania.