EFFECT OF BEAUVERIA-BASSIANA (FUNGI, HYPHOMYCETES) ON FECUNDITY OF THE RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE)

Ten-d-old apterae of Russian wheat aphid, Diuraphis noxia Kurdyumov, (25 per treatment) were inoculated with conidial suspensions (10(6) conidia per ml) of Beauveria bassiana (Balsamo) Vuillemin, isolate SGBB 8601, or with sterile water, then caged individually on wheat seedlings. Temperature was maintained at 22 +/- 3-degrees-C, and relative humidity was kept at greater-than-or-equal-to 95% for 24 h and almost-equal-to 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. bassiana significantly 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 did Beauveria-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.