Development of Metarhizium humberi in Aedes aegypti eggs

The entomopathogenic fungus Metarhizium humberi affects Aedes aegypti adults, larvae and eggs, but its ovicidal activity is not yet well documented. Conidia of this fungus adhered to the chorion, initiated germination within 12 h, and germinating conidia were detected for up to 10 d after contact with the egg. Germ tubes either penetrated the chorion directly or formed appressoria at the end of a short hypha (<5 μm) or, subsequently, on longer, branched hyphae. Thin layers of what was most probably a fungal mucilaginous excretion were detected on the chorion adjacent to germ tubes, appressoria and hyphae. After 5 d eggs frequently appeared shriveled with ruptures in the chorion, and with the interior filled with hyphae that eventually produced mycelium and new conidia on the egg surfaces. Findings demonstrated that this fungus can infect A. aegypti eggs and subsequently recycle on their surface by producing large numbers of new conidia that should be infective for further generations of eggs, larvae and adults.