The aim of this study was to observe the colonization of the guts of germ-free desert locusts, Schistocerca gregaria, by Pantoea agglomerans, the dominant bacterial species found in the mature adult. P. agglomerans was established as a monoculture. During the first generation of the monoassociated locusts the bacterial population remained at a low level despite daily inoculations from Days 32-46. By the second generation, without additional inoculations of P. agglomerans, some insects had a large monoflora. However, there was a wide variation, indicating that the bacteria had successfully colonized some insects but not others. In contrast colonization of conventionally reared insects was rapid and occurred within days of hatching. The possible reasons for the difficulty in establishing P. agglomerans in the guts of germ-free locusts are discussed.