Natural Prevalence of Entomopathogenic Fungi in Hibernating Pupae of Cameraria ohridella (Lepidoptera: Gracillariidae) and Virulence of Selected Isolates

Spontaneous infection of hibernating Cameraria ohridella pupae by entomopathogenic fungi was monitored at two localities of south-western Slovakia and efficacy of selected fungal isolates against the pupae was evaluated in laboratory. Natural prevalence of fungal infection in pupal populations was low (< 7%) and varied depending upon collecting date, locality, year, and pathogen. Ten isolates of three fungal species, Beauveria pseudobassiana, Isaria fumosorosea, and I. farinosa, isolated from the naturally infected pupae and three isolates of non-insect origin of two fungi, B. bassiana and Metarhizium anisopliae, were screened for colony growth, conidial production in vitro, and virulence to C. ohridella pupae. A significant variability in the evaluated traits was detected among the isolates. Pupae demonstrated vulnerability to all the isolates irrespective of their origin, however virulence of isolates varied significantly. I. fumosorosea was the most virulent fungus with median lethal concentration of 0.09 x 10(4) conidia/ml (isolate CO10-IFu) and mean survival time of pupae of 7.14 days (isolate CO8-IFu). No correlation between conidial yield of isolates and fungal virulence was observed, but a moderately strong relationship was detected between virulence and mycelial growth rate of isolates.