Observation of infection process of Isaria fumosorosea to Plutella xylostella with transmission electron microscopy

Key Words：Plutella xylostella, Isaria fumosorosea, infection process, propagation ways, transmission electron microscopy

Abstract：            To demonstrate the process of infection of Plutella xylostella(L.) (Lepidoptera: Plutellidae) by the indigenous strain EBCL 03011 of the fungus Isaria fumosorosea (=Paecilomyces fumosoroseus) (Hypocreales: Cordycipitaceae) 4th instar larvae of P. xylostella were experimentally infected with a fungal suspension (1× 10⁷ conidia/mL) and organs such as the integument, midgut and muscle tissues subsequently examined by transmission electron microscopy. Histopathological analyses revealed that conidia of I. fumosorosea germinated 1 h postinoculation resulting in appresorium formation ultimately penetrating the integument of P. xylostella 4 h after inoculation. The hyphal bodies had spread into the body cavity 24 h after inoculation. The penetrating hyphae of I. fumosorosea produced a number of granular hyphal bodies by budding or septation, and became distributed throughout the cuticle and hemocoel of the infected larvae. The penetration and propagation of the hyphal bodies was achieved by a combination of mechanical pressure and enzymatic action during the infection process.