SUMMARY Trypanosoma cruzi , causative agent of Chagas disease, co-infects its triatomine vector with its sister species Trypanosoma rangeli , which shares 60% of its antigens with T. cruzi . Additionally, T. rangeli has been observed to be pathogenic in some of its vector species. Although T. cruzi–T. rangeli co-infections are common, their effect on the vector has rarely been investigated. Therefore, we measured the fitness (survival and reproduction) of triatomine species Rhodnius prolixus infected with just T. cruzi , just T. rangeli , or both T. cruzi and T. rangeli . We found that survival (as estimated by survival probability and hazard ratios) was significantly different between treatments, with the T. cruzi treatment group having lower survival than the co-infected treatment. Reproduction and total fitness estimates in the T. cruzi and T. rangeli treatments were significantly lower than in the co-infected and control groups. The T. cruzi and T. rangeli treatment group fitness estimates were not significantly different from each other. Additionally, co-infected insects appeared to tolerate higher doses of parasites than insects with single-species infections. Our results suggest that T. cruzi–T. rangeli co-infection could ameliorate negative effects of single infections of either parasite on R. prolixus and potentially help it to tolerate higher parasite doses.