EARLY EVENTS IN THE INFECTION OF A HELICOVERPA-ZEA CELL-LINE BY NOSEMA-FURNACALIS AND NOSEMA-PYRAUSTA (MICROSPORA, NOSEMATIDAE)

We compared the early events in the in vitro development of two micros poridia, Nosema pyrausta and Nosema furnacalis, that infect the Europe an and Asian corn borers, Ostrinia nubilalis and Ostrinia furnacalis, respectively. Spores of both species, produced in O. nubilalis larvae, were activated in alkaline saline solutions and used to infect the He licoverpa tea cell line BCIRLHZAM1. In both N. pyrausta and N. furnaca lis incubated at 31 degrees C, the first sporogonic cycle resulted in the differentiation of early spores that germinated intracellularly. N . pyrausta showed a 24-hr lag phase followed by a growth phase during which meronts had an approximate doubling time of 8 hr. Early spore di fferentiation began at 48 hr pi, and by 72 hr pi infected cells were f illed with empty spores. There was a single increase in the percentage of N. pyrausta infected cells at 72 hr pi as early spore production c eased and the late spores that differentiated subsequently did not ger minate intracellularly. In contrast, N. furnacalis had a 12-hr lag pha se followed by a growth period when meronts had an approximate doublin g time of 4 hr. Early spore differentiation was observed 24 hr pi, and at 34.5 hr pi most infected cells were filled with empty spore cases. Subsequently, N. furnacalis also differentiated late spores but conti nued to produce early spores leading to continued cross-infection of h ost cells by N. furnacalis during a 7-day culture period. These result s indicate that N. pyrausta and N. furnacalis differ from one another in their patterns of growth and sporogony in H. tea cell cultures. (C) 1996 Academic Press, Inc.