The neogregarine, Mattesia oryzaephili, is pathogenic for several stored-grain pest insects, including the sawtoothed grain beetle, Oryzaephilus surinamensis and the rusty grain beetle, Cryptolestes ferrugineus. It also infects their respective bethylid parasitoids, Cephalonomia tarsalis and Cephalonomia waterstoni. Male wasps do not attack the beetle larvae and do not become infected, but the disease is transmitted per os to nearly all female wasps when they paralyze or feed on infected hosts. The mean survival time of diseased C. tarsalis after exposure to heavily infected O. surinamensis was 20 d. For C. waterstoni that were infected via C. ferrugineus, the mean survival time was 36.1 d, as opposed to 45.9 d for uninfected C. waterstoni. The long survival time of infected wasps allows for parasitoid oviposition and some transmission. The wasps oviposit on beetle larvae that have early stage infections, and their progeny succumb to the infection. They do not oviposit on beetle larvae with late stage infections that are macroscopically visible under ultraviolet illumination. Living wasps may transmit the disease to beetles through their frass and serve as a dispersal vehicle and a source of inoculum after death.