Abstract
A spore shower technique was used to test four species of aphid-derived entomophthoralean fungi, Pandora neoaphidis (Remaudiere & Hennebert) Humber, Zoophthora radicans (Brefeld) Batko, Conidiobolus thromboides Drechsler, and Conidiobolus coronatus (Constantin) Batko, against the cereal aphids, Diuraphis noxia (Mordvilko) and Metopolophium dirhodum (Walker). Six endemic and five foreign isolates of the four fungal species were tested. There was variability in virulence among different isolates and species of the fungi and in susceptibility between the two aphid species. Low LC50's (i.e., high virulence) were produced with two C. coronatus isolates (2.2–4.0 spores/mm2), three C. thromboides isolates (2.3–13.2 spores/mm2), and two P. neoaphidis isolates (1.4–8.1 spores/mm2). Two Z. radicans isolates exhibited moderate virulence with LC50's ranging from 25.1 to 46.8 spores/mm2. Two isolates of C. thromboides that had been in long-term storage displayed relatively low virulence. Aphid colonies on leaves were more suitable for bioassays than aphids confined in wire mesh inoculation chambers. The latter were disadvantageous. because the aphid movement within the chamber adversely affected the determination of fungal inoculum exposure rates. These conditions also often induced the production of resting spores instead of primary conidia.
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