A microsporidan parasite of the forest tent caterpillar Malacosoma disstria infected cells and replicated in vitro in a line from the moth Heliothis zea. After spore germination, the incidence of infected cells increased with time until leveling off with sporulation. During the first 24 hr, there was a static number of parasites, followed by a 2-day logarithmic growth phase during which the population doubled five to six times. The growth rate was 9 to 11 hr per population doubling. Sporulation commenced on day 3, and 40 to 50 spores were recovered from each infected cell. The life cycle was completed within 6 days, culminating in spores that were infectious for cultured cells. The antibiotic fumagillin at a dose of 1 ppm in the culture medium was microsporida-static.
Bibliographical noteFunding Information:
This investigation was supported by U. S. Public Health Service Research Grant No. AI 09914 from the National Institute of Allergy and Infectious Diseases. This is Paper No. 9423, Scientific Journal Series, Minnesota Agricultural Experiment Station.