Standardized bioassay and screening of Beauveria bassiana and Paecilomyces fumosoroseus against the Russian wheat aphid (Homoptera: Aphididae)

Two hyphomycetous fungi with potential as biocontrol agents were used in bioassays against the Russian wheat aphid, Diuraphis noxia (Kurdjumov). Dose-response assays were done using 5-7 concentrations of 2 isolates each of Beauveria bassiana (Balsamo) Vuillemin and Paecilomyces fumosoroseus (Wize) Brown and Smith. A sensitive assay technique was developed in which adult aphids, 0-2 d of age, were sprayed with fungal spore suspensions on cut barley leaf sections. LC50 estimates were 91 and 282 spores per square centimeter for two B. bassiana isolates and 46 and 56 spores per square centimeter for two P. fumosoroseus isolates. Slopes ranged from 1.43 to 1.76. Aphids were significantly less susceptible to B. bassiana than to P. fumosoroseus, indicated by the lack of overlap among fiducial limits. LT50s varied inversely with dose for all 4 isolates and ranged from 4.6 d to 12.2 d for B. bassiana, and from 3.3 d to 12.2 d for P. fumosoroseus, depending on isolate and dose. In standardized screening assays, relative potencies ranged from 0.2 to 2.1 among 23 isolates of B. bassiana and from 0.3 to 3.7 among 14 isolates of P. furmosoroseus. Use of this assay method will facilitate studies of biotic and abiotic factors that influence Russian wheat aphid susceptibility to fungal infection in the laboratory and in the field