Abstract Bioassays of two entomophthoralean fungi, Pandora delphacis and P. neoaphidis, were conducted on the green peach aphid, Myzus persicae. For inoculation, batches of ≤3-day-old nymphs on detached cabbage leaves were exposed to conidial showers of varying time lengths from sporulating fungal mats produced in liquid culture. Eight dosages of each pathogen were used to inoculate 88–345 nymphs each. The nymphs inoculated were maintained at 18–20°C 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 parameters for time and dose effects of the two fungal species. P. delphacis killed the aphid more rapidly than P. neoaphidis, though both had similar slopes for dose effect. The values of LD 50 estimated on days 3–7 after exposure decreased from 18.1 to 0.9 conidia/mm 2 for P. delphacis and from 17.0 to 0.04 conidia/mm 2 for P. neoaphidis. The estimates of LT 50 for the two pathogens were similar at dosages of more than 5 conidia/mm 2 but differed at lower dosages. Based on the time–dose–mortality relationships fitted and the virulence indices estimated, P. delphacis is a promising microbial agent for aphid control and is competitive with P. neoaphidis.