—Midgut trypsin and lectin levels were determined in three tsetse species, namely Glossina morsitans morsitans, G. longipennis and G. fuscipes fuscipes. In addition, the abilities of midgut homogenates prepared from these flies to transform bloodstream-form Trypanosoma brucei brucei and T. congolense were compared in vitro. In all the species examined, trypsin levels did not differ significantly up to 24 h post-bloodmeal. There were similar rates of transformation of the bloodstream-form trypanosomes into procyclic (midgut) forms in vivo, so that all species had similar levels of infection in the midgut. However, trypsin levels continued to increase beyond 24 h, reaching a peak between 48 and 72 h. The peak was lowest in G. m. morsitans. The midgut homogenates in this species also had the lowest levels of lectin. The species had the highest levels of mature T. congolense and T. brucei infections. We propose that the lower levels of peak midgut tryspin and lectin in G. m. morsitans is important in the establishment of trypanosome infections in this species of tsetse.
