The effects of beauvericin, a toxic fungal metabolite common contaminant of maize and wheat, on aphid fitness were studied in three consecutive generations of females. Aphids were reared on wheat leaves inserted into a sandy substratum wetted with a solution of beauvericin. Ingestion of this solution through leaves did not significantly decrease the lifespan of females of all generations as compared to controls. However, the mean number of offspring from the third generation of treated females was significantly smaller than those in controls. Furthermore, treated second and third generation females produced a greater number of abortive embryos. Histological analysis revealed abundant DAPI and Feulgen positive material in the cytoplasm of some bacteriocytes of treated third generation females. This material was attributed to the endosymbionts of bacteriocytes. Tests by contact were also carried out and revealed a significantly lower survival of treated first instar aphids as compared to controls 18 h after the start of the trial.