Integration of sterile insects and pesticides for the control of the tsetse fly. Glossina morsitans morsitans

The effectiveness of integrating conventional insecticidal control with the release of sterile insects was tested in Tanzania with laboratory-reared Glossina morsitans morsitans. Two aerial applications of endosulfan suppressed the adults of an initial population of about 260,000 morsitans and 120,000 Glossina pallidipes by more than 95% on each application. Irradiated morsitans pupae were then distributed twice weekly in numbers depending on the varying density of the natural population within a 200-square kilometre test plot, averaging about 135 sterile males per square kilometre per month. After six months the check population of pallidipes had returned to normal density (0% control), but morsitans was only at 10% of its normal level (90% control). Although further reduction of morsitans was prevented by immigration of flies, 85-90% control was maintained throughout the remaining seven months of releases. The sterile males were highly competitive, preventing population increase at a ratio of about 1 sterile male: 1 indigenous male; eradication would probably have been achieved if migrating fertile flies had not penetrated the perimeter. The sterile males were supplied from a self-sustaining colony of about 60,000 flies of Tanzanian origin maintained in insectaries at Tanga. The female flies produced 5-6 pupae each with a mean weight of 29 mg; these 45,000 females produced sufficient progeny for about 27,000 sterile males to be liberated monthly. For each 100,000 pupae produced, 31,800 viable males were released at a cost of US 220 per thousand. Half of this cost was for host animal maintenance; approximately 580 locally procured or bred goats and 130 rabbits of imported origin were maintained indoors. Tanga strain flies reared in vitro at the International Atomic Energy Agency in Vienna in a 10,000-fly, back-up colony also performed normally when tested independently in the field. (author)