Abstract
Spruce budworm, Choristoneura fumiferana, are often naturally infected with the microsporidan parasite Nosema fumiferanae and this is frequently carried over into laboratory stock. The presence of N. fumiferanae infection seriously interferes with the study of other pathogens. The antibiotic compound Fumidil B has recently been used to control infection in Ostrinia nubilalis (European corn borer) by the microsporidan Perezia pyroustae (Lewis and Lynch 1970) and infection in Anthonomus grandis (boll weevil) by an unidentified microsporidan (Flint et al. 1972).