SOME ASPECTS OF THE EPIDEMIOLOGY OF A MIGROSPORIDIAN PARASITE OF THE SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA (CLEM.)

Abstract

Limited tests indicate that the microsporidian parasite Perezia fumiferanae is restricted to insect hosts of the genus Choristoneura and for practical purposes to the single species Choristoneura fumiferana (Clem.). Frozen spores of this parasite were found to be infectious longer than those kept under other conditions but no spores were infectious after 6 months' storage. There are two distinct methods of infection, oral and congenital. Immature eggs within infected female insects are infected by schizonts which develop into spores after the eggs are laid. All infected females, regardless of the degree of infection, transmit the parasite to their offspring, and for practical purposes all the progeny of such females are infected. Offspring of heavily infected females appear to contain more spores than those of lightly infected females. Infected males are sometimes capable of transmitting the parasite to a portion of their offspring. Congenital transmission is responsible for the passage of the parasite from host generation to generation. Increase in the incidence of the parasite occurs by oral ingestion of spores but the habits of the host larvae restrict most transmission to the late larval instars.