Four blesbok culled in the Rietvlei Nature Reserve, Pretoria, District during May 1972 were found to harbour large burdens of 1st instar Oestrus spp. larvae and from 16-37 3rd instar larvae of Oestrus macdonaldi. They were also infested with large numbers of 1st instar Gedoelstia hässleri larvae but only 2 harboured 3rd stage larvae of this species.
During an 18-month period 34 blesbok were culled in pairs in the Percy Fyfe Nature Reserve, Potgietersrus District. These antelope harboured peak numbers of 1st instar Oestrus spp. Larvae during February, July and December but few if any during early October. Third instar Oestrus variolosus larvae were generally recovered from July-February and those of 0. macdonaldi during July 1972 and from May-September 1973. Some 1st instar larvae of these flies appeared to undergo a pulmonary migration before returning to the naso-pharyngeal area to mature. The pupal period of 0. variolosus varied from 67 days during the spring to 35 days during the summer. G. hässleri larvae reached peak numbers from October 1972-January 1973 and during May and June 1973. The lowest numbers were recovered from August-October 1973. Recovery and measurement of 1st ins tar larvae indicated that they either undergo an ocular-cranial or ocular-vascular-pulmonary migration before reaching the naso-pharyngeal area. Pupal periods varied from 46 days for flies hatching during October to 22 days for those hatching during December.