Study of the virulence and conidial germination types for some Beauveria bassiana isolates

In the present study, some isolates of Beauveria bassiana were isolated from different soil samples and their virulence was investigated against Sunn pest Eurygaster integriceps (Hem., Scutelleridae), flour moth, Ephestia kuehniella (Hym., Pyralidae), and king meal worm, Zophobas morio (Col., Tenebrionidae). Twenty three isolates were isolated using Galleria-baiting method from collected soil samples in different regions; Karaj, Urmia, Mako and Dezful and were identified. The insect hosts were infected using dipping method. The results showed that the fifth nymphal instars of Sunn pest and fourth larval instars of flour moth were susceptible to all isolates of B. bassiana while last larval instars of the beetle were resistant and no mortality was observed. The most virulent isolates were TV and TZ with approximately 90% mortality on E .kuehniella and E. integriceps. The isolates were categorized broadly into three classes: low virulent (0-33% mortality), medium virulent (34-67% mortality) and high virulent (68-100% mortality). On PDA medium, two distinct germination types of conidia were revealed including conidia with single and dual germ tubes. There were significant differences among isolates in their percentages of germination types but there was no significant correlation between virulence and conidial germination types.