INSTABILITY IN PATHOGENICITY OF ENTOMOPHAGA-MAIMAIGA AFTER LONG-TERM CRYOPRESERVATION

Three isolates of Entomophaga maimaiga, a fungal pathogen of gypsy mot h (Lymantria dispar), were stored immersed in liquid nitrogen (-196 C) as naturally occurring protoplasts for approximately 7 years. All iso lates survived although with diminished ability to produce conidia and azygospores. Days from infection to host death increased for all isol ates after the storage period. Soon after isolation, two of the isolat es differed in levels of azygospores produced at 25 C, while after sto rage, differences among isolates persisted but had changed; at 25 C, a ll isolates differed from each other in levels of conidial production, and one isolate no longer produced azygospores. Days from infection u ntil host death for one isolate were significantly longer in compariso n with other isolates both before and after storage, and this latter i solate also grew slowly in vitro as well as in vivo. Our results sugge st that further investigations are warranted to study potential change s in characteristics of pathogenicity during maintenance of fastidious fungal entomopathogens under liquid nitrogen in a culture collection.