Morphological alterations of Metarhizium anisopliae during penetration of Boophilus microplus ticks.

Chronological histological alterations of Metarhizium anisopliae during interaction with the cattle tick Boophilus microplus were investigated by light and scanning electron microscopy. M. anisopliae invades B. microplus by a process which involves adhesion of conidia to the cuticle, conidia germination, formation of appressoria and penetration through the cuticle. Twenty-four hours post-infection conidia are adhered and germination starts on the surface of the tick. At this time, the conidia differentiate to form appressoria exerting mechanical pressure and trigger hydrolytic enzyme secretion leading to penetration. Massive penetration is observed 72 h post-inoculation, and after 96 h, the hyphae start to emerge from the cuticle surface to form conidia. The intense invasion of adjacent tissues by hyphae was observed by light microscopy, confirming the ability of M. anisopliae to produce significant morphological alterations in the cuticle, and its infective effectiveness in B. microplus.