Bioassay of Entomophthora against the spotted alfalfa aphid Therioaphis trifolii f. maculata

Abstract

A method for the bioassay of Enthomophthora spp. against aphids is described. Twenty-four isolates comprising five species of fungi were screened for activity against Therioaphis trifolii f. maculata. The only isolates with a high level of activity were those of E. sphaerosperma obtained from aphids. The initial bioassays with E. sphaerosperma indicated that aphids, starved for 24 hr during inoculation with E. sphaerosperma primary spores, were less susceptible than those removed from the plants, for just the period of exposure to the primary spore shower. Using the latter procedure, five assays of the most pathogenic isolate gave a mean LC 50 of 11.3 primary spores/mm 2 while bioassays of four other isolates gave LC 50 values ranging from 15.7 to 27.3 spores/mm 2. The potential of E. sphaerosperma as a microbial control agent for T. trifolii f. maculata in Australia is discussed.