STERILIZING TSETSE (DIPTERA, GLOSSINIDAE) IN THE FIELD - A SUCCESSFUL TRIAL

The juvenile hormone mimic, pyriproxyfen, applied topically to female tsetse flies, Glossina morsitans morsitans Westwood and G. pallidipes Austen, effectively sterilizes them by arresting development of their offspring in the pupal stage. Between July and November 1989, 41 odour baited traps treated with pyriproxyfen were deployed near Rekomitjie Research Station, Zambezi Valley, Zimbabwe, in a 12.3 km2 block of woodland habitat of G. m. mositans and G. pallidipes. Tsetse entering the traps brushed against material dosed with 2 mg/cm2 pyriproxyfen and were then allowed to escape. Emergence rates from pupae of the two species collected in the block fell to 30% and 2.7%, respectively, of control levels after three months. Of more than 750 pupae of each species dissected 78% and 94%, respectively, showed incomplete development. The average ovarian age category of female G. pallidipes sampled in the block doubled during the trial. This was due to immigration of older flies and the declining birth rate which, if sustained over a large area for a year, was estimated as sufficient to cause a population reduction to 10(-6) of its original level.