VIRULENCE OF VERTICILLIUM-LECANII AND AN APHID-DERIVED ISOLATE OF BEAUVERIA-BASSIANA (FUNGI, HYPHOMYCETES) FOR 6 SPECIES OF CEREAL-INFESTING APHIDS (HOMOPTERA, APHIDIDAE)

An aphid-derived isolate of Beauveria bassiana (SGBB8601) and Verticillium lecanii (DNVL8701) were bioassayed against six species of globally distributed cereal-infesting aphids under controlled conditions. Aphids were immersed in conidial suspensions at concentrations ranging from 104 to 108 conidia/ml, each concentration being replicated six times with 20 aphids treated per replicate. Pathogenicity of both fungal species was confirmed on all the aphids tested, but in most cases, B. Bassiana was more virulent than V. Lecanii. The LC50 values for B. Bassiana and V. Lecanii were 8.2 × 104 and 4.1 × 105 conidia/ml, respectively, on Diuraphis noxia; 2.1 × 105 and 9.8 × 105 on Schizaphis graminum; 3.3 × 105 and 7.0 × 105 on Metapolophium dirhodum; 1.1 × 105 and 1.3 × 106 on Sitobion avenae; 2.1 × 106 and 8.9 × 105 on Rhopalosiphum maidis; and 3.3 × 106 and 6.9 × 106 on R. Padi. Statistical analysis indicated that there were substantial differences in susceptibility to the two pathogens and in virulence of each fungus to different aphid species. The LT50 values at all concentrations varied between the pathogens and among the aphid hosts with B. Bassiana tending to kill aphids more rapidly. The mortality data were probit transformed, and a third-order polynomial model was fit to the data to describe responses of each host to conidial concentration and time after treatment. The potential for use of B. Bassiana for aphid control is discussed. © 1990 Entomological Society of America.