The gregarine, Leidyana canadensis Clopton and Lucarotti was found infecting the guts of larvae in a declining population of the hemlock looper, Lambdina fiscellaria fiscellaria (Guenée), in Charlotte County, New Brunswick. Total mortality, in rearing, of field-collected larvae and pupae was 75.5% in 1993 and 89.2% in 1994. Leidyana canadensis infections were present in 60.1 and 80.5% of these dead insects in the two respective years. The incidence of L. canadensis in larvae that died in rearing was greater than 50% for all instars except those collected in the fifth instar, where the incidence was below 30%. Gregarine infections were present in first-instar larvae on the first days of collection for both years and, in 1994, 74% of all first-instar larvae collected were infected with L. canadensis. Of 678 larvae collected in 1994, 73 survived to adults and, of these, 44 had harbored L. canadensis as larvae. The incidence of other microbes and parasitoids in dead larvae and pupae is also reported.
