The fine structure of Entomophthora apiculata and its penetration of Trichoplusia ni.

Abstract

The fine structure of conidia and immature resting spores of the entomogenous fungus Entomophthora apiculata is described. The two cell types contain comparable organelles and quantities of lipid, and possess a similar cell wall structure. The large quantity of stored lipid and numerous mitochondria in each cell type indicate a capacity for great metabolic activity. Numerous dense, microbody-like organelles were observed in conidia and resting spores, and their possible functions are discussed. Third instar larvae of the cabbage looper Trichopulsia ni were exposed to conidia of E. apiculata. Fungal germ tube formation and penetration of the host integument were observed. The germ tubes did not form appressoria and appeared to penetrate the epicuticle by enzymatic and physical means. After penetration of the epicuticle the germ tube often bifurcates, and expands as two or more digit-like projections parallel to the lamellae of the exocuticle. The hyphae gradually extend inward, cleaving the lamellae of cuticle, and eventually enter the host's body cavity.