Biological characteristics of selected Erynia neoaphidis isolates

Four isolates of the entomopathogenic fungus Erynia neoaphidis, from differ ent hosts and locations in Switzerland, were distinguished by their DNA fra gment banding pattern obtained by RAPD-PCR. The isolates differed in sporul ation and germination rates, but not in virulence (overall mean LD50 16 con idia mm(-2)) against the aphid Acyrthosiphon pisum. The sporulation rate wa s 6 to 24 conidia mm(-2) 10 min(-1). On nutrient agar, 24-73 % of the conid ia produced secondary conidia and 32-68 % produced germ-tubes on polystyren e. Differentiation of primary into secondary conidia or germ-tubes is possi bly dependent on the presence of free water on the contact surface; on a dr y surface, conidia germinated mostly with a germ-tube, whereas on a wet sur face the conidia produced a secondary conidium. Experimental support is pro vided for the claim that, in addition to LD50 values, features such as spor ulation rate, spore germination, capacity to form secondary conidia and int raspecific variation should be considered in selecting isolates of E. neoap hidis for biocontrol agents.