Fungal Pathogens

Unlike the other groups of insect pathogens that generally infect the host when infective propagules are ingested, entomopathogenic fungi almost always invade their insect hosts by penetrating directly through the cuticle. The fungal spore first adheres to the cuticle and, under appropriate conditions, germinates; the germ tube penetrates the cuticle of the host and enters the hemocoel. Vegetative structures multiply in the hemocoel of the insect host, often in the form of yeast-like hyphal bodies that reproduce by budding. As the hemocoel becomes filled with hyphal bodies, the insect usually dies, and the fungus continues to develop saprophytically. After the body of the dead insect is filled with mycelia, fruiting structures emerge from the cadaver and produce infectious spores. At this point the dead insect has the consistency of a moist loaf of bread and, depending on the color of the spores or conidia, may appear white or some darker color. This is the stage of the fungal infection commonly observed in the field. This dead caterpillar is typical of an insect killed by a fungal infection.

Tanada and Kaya (1993) listed 8 classes, 13 orders and 57 genera that contain entomopathogenic species of fungi. As one would expect, many of these genera are very specialized and do not conform to the generalized life cycle described above. There are five major groups of fungi, the Flagellate fungi or Chytridiomycetes, the Oomycetes (also flagellate but also not true fungi), the Zygomycetes, the Ascomycetes, and the Basidiomycota. Two of these, the Zygomycota and the Ascomycota contain common insect pathogens that are also useful in biological control programs.




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This page was last updated May 29, 2004