Bioassays of two entomophthoralean fungi, Pandoradelphacis and P. neoaphidis, were conducted on thegreen peach aphid, Myzus persicae. For inoculation,batches of I3-day-old nymphs on detached cabbageleaves were exposed to conidial showers of varyingtime lengths from sporulating fungal mats produced inliquid culture. Eight dosages of each pathogen wereused to inoculate 88-345 nymphs each. The nymphsinoculated were maintained at 18-20℃ and L:D (12:12) at high humidity and were examined daily for mortality.The resulting data were analyzed using a time-dose-mortality modeling technique, yielding the parametersfor time and dose effects of the two fungalspecies. P. delphacis killed the aphid more rapidlythan P. neoaphidis, though both had similar slopes fordose effect. The values of LD50 estimated on days 3-7after exposure decreased from 18.1 to 0.9 conidia/mm2for P. delphacis and from 17.0 to 0.04 conidia/mm2 for P.neoaphidis. The estimates of LT50 for the two pathogenswere similar at dosages of more than 5 conidia/mm2 but differed at lower dosages. Based on the time-dose-mortality relationships fitted and the virulenceindices estimated, P. delphacis is a promising microbialagent for aphid control and is competitive with P.neoaphidis.