The fungus Metarrhizium anisopliae develops through at least 6 identifiable stages on or in a larval elaterid host: (1) an external conidium which is the infective stage; (2, 3, 4) appressorial, penetrant plate, and penetrant hyphal body stages which are involved in the prolonged penetration of the extensive cuticle; (5) a coelomic hyphal body stage for proliferation and spread of the fungus within the body cavity of the host; and (6) a chlamydospore stage for maintaining the fungus viable within the dead, mummified host, until surface sporulation can occur and infective external conidia are produced.
Histolysis of cuticle by fungal enzymes appears to play a major role in cuticle penetration. Within the host, toxins produced by the fungus incite a progressive degeneration of the host tissues, with no appreciable swelling or shrinkage of host cells. The primary effect appears to be on the structural integrity of the membranes of the various cytoplasmic organelles. A rapid excretion of fluids by the Malpighian tubules and, to a more limited extent, by the midgut epithelial cells is indicated, which undoubtedly enhances desiccation and mummification of the host.