Ten-d-old apterae of Russian wheat aphid,Diuraphis noxiaKurdyumov, (25 per treatment) were inoculated with conidial suspensions (106conidia per ml) ofBeauveria bassiana(Balsamo) Vuillemin, isolate SGBB 8601, or with sterile water, then caged individually on wheat seedlings. Temperature was maintained at 22 ± 3°C, and relative humidity was kept at ≥95% for 24 hand ≈85% subsequently. Each aphid was monitored daily over 14 d for mortality and nymph production. All newborn nymphs and dead adults were removed and plated. The experiment was performed four times.B. bassianasignificantly increased aphid mortality (mean mortality due to mycosis, 82%). Over the 14-d period, untreated adults produced significantly more nymphs (37.8 ± 4.5) (mean ± SE) than didBeauveria-treated adults (14.3 ± 1.6). However, the pathogen did not affect nymph production by individual aphids (mean, 3.3 nymphs per d per aphid for both treatments). Thus, treatment differences in total reproduction were caused by differential mortality rather than differential reproduction rates of individuals. Most (>99%) nymphs produced from infected adults were uninfected.