Infection of the formosan subterranean termite, Coptotermes formosanus Shiraki, by the entomopathogenic fungus Isaria fumosorosea

this study investigates Isaria fumosorosea (Ifr) infection of and transfer among Formosan subterranean termites (FST). Prior to fungal exposure nestmates were fed Nile Blue, dye or Neutral Red dye. Blue FST were exposed to 6.3 x 10⁹ fungal spores and mixed with red nestmates. At timepoints up to 168 h, termites were removed from each dyed group and fixed with osmium tetroxide. SEM observation at 24 h post-exposure showed most fungal conidia ungerminated and on the external cuticle of blue FST. At 48 h, germ tubes had formed on blue FST and penetrated the cuticle. Hyphae were observed externally at 96 h post-exposure. Fungal spores were visible on red FSt 96 h after placement with blue FSt, and hyphae were abundant at 168 h post-exposure. Blue FST were fixed, dehydrated, then embedded with a low viscosity epoxy. Embedded FST were sectioned with a microtome and visualized via light microscopy. Ifr penetrated the cuticle of blue FST at 48 h and were found on the interior of termites after 72 h. Transfer to red FST was confirmed 96 h post-exposure through visualization of spores.