Fusarium xyrophilum facilitates its dispersal by exploiting sensory biases of generalist insects through pseudoflowers

The fungus Fusarium xyrophilum produces flower-like structures (i.e. pseudoflowers) composed entirely of mycelia on yellow-eyed grasses (Xyris spp.), including X. surinamensis in Guyana. Whether these pseudoflowers function as true mimics that attract insects for fungal propagule dispersal remains unknown. We evaluated the potential of F. xyrophilum to influence insect visitation patterns by (i) documenting insect visits to real flowers and pseudoflowers on X. surinamensis in the field in Guyana, (ii) assessing the presence of F. xyrophilum DNA on insect bodies, and (iii) analyzing volatile emissions from flowers and pseudoflowers. During our field work, a broad range of generalist insects (i.e. Vespidae, Formicidae, Salticidae, Acrididae, and Tetrigidae) visited the flowers and pseudoflowers, which notably shared some insect visitors (i.e. meadow katydids, carpenter ants, and geometer moths). Some of these insects were observed chewing on the flowers and pseudoflowers. Fusarium xyrophilum DNA was detected on the bodies of captured insects using conventional and quantitative polymerase chain reaction (PCR). Volatile profiles of pseudoflowers and flowers were largely similar, except for a sesquiterpene, putatively identified as α-gurjunene, which was emitted by pseudoflowers and pure cultures of F. xyrophilum but not Xyris flowers. These findings support the role of insect visitors as vectors of F. xyrophilum propagules and suggest that the fungus may attract and use generalist insects by exploiting their preexisting sensory biases for Xyris floral signals rather than true mimicry.