Distribution of termite egg-mimicking fungi (“termite balls”) in Reticulitermes spp. (Isoptera: Rhinotermitidae) nests in Japan and the United States

Abstract

A termite egg-mimicking fungus was discovered in nests of the Japanese subterranean termite Reticulitermes speratus in 1997 and was reported for the first time in 2000. This fungus has a mutualistic relationship with termites. When termite workers recognize eggs laid by queens, they gather the eggs to tend them. The corticioid fungus Fibularhizoctonia sp. forms sclerotia that morphologically and chemically mimic termite eggs. By mimicking eggs, the fungus is protected and may be transported by termites to a competitor-free habitat. In turn, the sclerotia enhance egg survival, probably because the antifungal and antibacterial compounds produced by the fungus protect the eggs from putative pathogens. This novel termite-fungus interaction has previously been reported only in R. speratus in Japan. In this study, I conducted wide-range sampling in Japan and the United States to investigate the distribution of egg-mimicking fungi in five Reticulitermes spp. Here I show that R. flavipes and R. virginicus in the United States, as well as R. speratus, harbor the egg-mimicking fungus. No egg-mimicking fungi were found in R. okinawanus in Okinawa and R. hesperus in California. A BLAST homology search for rDNA sequences categorized the egg-mimicking fungi isolated from R. flavipes and R. virginicus as a species of Fibularhizoctonia.