ABSTRACT
The infection of Frankliniella occidentalis by two isolates of the entomopathogenic fungus Metarhizium anisopliae was studied using fluorescence, scanning, transmission, and confocal scanning laser microscopy techniques. Conidia of M. anisopliae adhered mostly to the wings of adult F. occidentalis but the number declined from 73 to 40% within 72 h postinoculation at 23 degreesC, presumably due to preening. Conidia germinated and produced appressoria on adult, larval, and pupal stages within 12 h post inoculation. However, penetration pegs were not observed until 30 h postinoculation. Light microscopy and transmission electron microscopy provided further information on fungal development inside the insect. The fungus colonized the insect hemocoel from day 3 and sporulated approximately 6 days postinoculation. Copyright 1999 Academic Press.
ABSTRACT
Gypsy moth hemocytes phagocytosed and/or encapsulated walled entomophthoralean cells and protoplasts that were regenerating cell walls but rarely recognized the healthy protoplasts that lack cell walls. Experiments using lectin conjugates demonstrated different sugars localized at the surface of protoplasts, regenerating protoplasts, and walled cells. Protoplasts had few sugars, in small amounts, on their surfaces and these fungal cells evoked minimal cellular responses. Walled fungal cells had greater quantities of a variety of sugars in the cell walls and evoked the strongest defense response. Protoplasts of Entomophaga grylli, an orthopteran pathogen that cannot successfully develop in the gypsy moth, Lymantria dispar, evoked a stronger hemocytic response in larvae than protoplasts of the lepidopteran pathogen Entomophaga maimaiga that is able to successfully develop in L. dispar. Sugars detected at the surface of E. grylli and E. maimaiga protoplasts were similar, so it is likely that the surface sugars we tested do not determine the differences in nonpathogen recognition between these fungal species.
ABSTRACT
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.
