Cytology of Leidyana canadensis (apicomplexa: eugregarinida) in Lambdina fiscellaria fiscellaria larvae (lepidoptera: geometridae).

The eugregarine Leidyana canadensis infects the larval gut of the eastern hemlock looper, Lambdina fiscellaria fiscellaria. Guts of infected larvae were chemically fixed, embedded in epoxy resin, and sectioned for light and electron microscopy to describe the cytology of L. canadensis and its pathology in the larval host. Oocysts of L. canadensis are ingested by larval hemlock looper. Trophozoites emerge from the oocysts, pass through the peritrophic membrane into the ectoperitrophic space, and attach to the epithelium of the midgut by means of an apical epimerite. The epimerite does not actually penetrate the affected epithelial cell; instead, it causes an invagination of the plasma membrane of the cell. The center of the epimerite contains membrane cisternae, and mitochondria line its periphery. Microtubules and mitochondria in the host cell cytoplasm surround the epimerite. At the light microscopic level, there appeared to be septa between the epimerite and the protomerite and between the protomerite and the deutomerite; however, in the electron microscope, no septa were evident. Only differences in the concentrations and nature of the inclusions in the cytoplasms of these three regions were apparent. The deutomerite contains a single nucleus in the central-posterior area. After an undetermined period, the epimerite detaches from the host gut epithelium and is withdrawn into the protomerite, and the trophozoites float freely in the ectoperitrophic space before differentiating into gamonts. Division of the single, large nucleus into numerous small nuclei appears to occur prior to syzygy. Gamonts pair and a cyst wall is laid down around them, forming a gametocyst. Oocysts are extruded from mature gametocysts, in chains, through sporoducts.