The Structure and Behavior of Gypsy Moth (Lymantria dispar) Hemocytes

Light and electron microscope observations of gypsy moth larval hemocytes show seven distinct and readily identifiable types of circulating cells: prohemocytes, granulocytes, coagulocytes, adipohemocytes, plasmatocytes, oenocytoids, and spherulocytes. In addition to these seven, a large, motile, highly refractive cell was observed with the light microscope, but little was elucidated about its ontogeny or function. Plasmatocytes, granulocytes, and coagulocytes constituted the largest portion of the hemocyte population. Plasmatocytes were distinguished by their large spindle shape and large dumbbell-shaped nuclei. These cells were motile and rapidly spread out on a glass microscope slide. Granulocytes characteristically contained secretory granules with a microtubular-filamentous substructure. They also contained vacuoles, microtubules, and substantial rough endoplasmic reticulum. Both plasmatocytes and granulocytes were phagocytic. The fragile coagulocytes were distinguished by the dilated perinuclear space, absence of granules, and by ejection of the nucleus from the cell. Spherulocytes contained refractive, membrane-bound inclusions with a crystal-like substructure and a central nucleus. Oenocytoids were typically large, with smooth, hyaline cytoplasm and a tiny eccentric nucleus. These particular cells increased in number just before and during ecdysis. Adipohemocytes contained numerous lipid globules of different sizes; these cells were particularly conspicuous in late instar larvae and pupae. Only the granulocytes and coagulocytes appeared to be important in coagulation. During this process the granular-floccular contents of the granulocytes were extruded by exocytosis while some cells lysed. Coagulocytes were probably the first to lyse. The coagulum was extremely sticky and trapped other hemocytes which subsequently lysed. The debris from these cells was a component of the coagulum which eventually became melanized.