Micro-organisms in the midgut of tsetse fly larvae

Two types of micro-organisms were found in the midgut of Glossina morsitans larvae, a large Gram-negative bacterial rod and a small Gram-negative rickettsia-like micro-organism, although the occurrence of the rickettsial type is restricted. The location of these micro-organisms in a small area of the proventriculus of all three larval instars is discussed. The large micro-organisms resemble milk-gland bacteria, and further evidence is presented in support of a milk transmission hypothesis for these micro-organisms.