REPRODUCTIVE RATES OF TSETSE-FLIES IN THE FIELD IN ZIMBABWE

Tsetse flies Glossina morsitans morsitans Westwood and G. pallidipes A usten were marked and released within 12h of emergence at Rekomitjie R esearch Station, Zambezi Valley, Zimbabwe, and on Redcliff Island, Lak e Kariba. Ovarian dissections were performed on recaptured flies and o n wild collected samples. At Rekomitjie >90% of female G. m. morsitans were inseminated by age 4 days and G. pallidipes by 7 days. For both species at both sites the length of the largest oocyte, for flies in o varian category zero, increased approximately linearly for about the f irst 6 days and was ovulated at c. 6-8 days. The largest oocyte grew s ignificantly more slowly in later cycles. For G. m. morsitans, but not for G. pallidipes, the rate increased with temperature; the rates wer e always higher than observed in the laboratory. At Rekomitjie, for bo th species and at a mean screen temperature of 22 degrees C, the first larva was produced at c. 18 days and subsequent larvae at 11-day inte rvals; the intervals decreased with temperature by c. 0.5 days/degrees C. On Redcliff Island the intervals for both species were 2 days shor ter than at Rekomitjie at any given screen temperature and were someti mes as short as 7 days. The length of the larva in utero increased exp onentially during pregnancy.