Tsetse populations and trypanosome prevalence in cattle were monitored from
1986 to 1993 in the Ghibe valley, south-west Ethiopia. From January 1991 to December 1993
between 2000 and 4000 cattle were treated at monthly intervals with a synthetic pyrethroid
insecticide, cypermethrin (RS-alpha-cyano-3-phenoxybenzyl (1RS)-cis, trans-3(2,2-
dichlorovinyl)-2,2-dimethylcyclopropane carboxylate). An approximate dosage of 1 ml per 10
kg bodyweight was used to control tsetse flies (Glossina spp.). Treatments were given as
`pour-on' applications along the backlines of animals, using automatic drench-gun
applicators. This resulted in a decline of 93 percent in the apparent density of G.
pallidipes Austen. A reduction of 83 percent in the apparent density of G. morsitans
submorsitans Newsted was also observed. This reduction was associated with a reduction in
trypanosome prevalence in cattle over 74 percent in 1993, despite a high level of
resistance to all available trypanocidal drugs. The numbers of Stomoxys spp. (Diptera:
Muscidae) and Tabanidae were also significantly reduced (P<0.01).