Fungus Exposed Solenopsis invicta Ants Benefit from Grooming

We investigated aspects of resistance to entomopathogenic fungi in the social insect Solenopsis invicta, the red imported fire ant (RIFA). RIFA reared individually were significantly more susceptible to the entomopathogenic fungi Metarhizium anisopliae var. anisopliae M09 than reared in groups. Fungus exposed ants performed more self-grooming behavior when isolated as individuals and received more allo-grooming when accompanied with four healthy nestmates. Using fluorescence microscopy, we counted the number of fluorescein isothiocyanate (FITC)-labeled conidia on the cuticle of fungus exposed ants reared individually or as groups. The number of conidia on the surface of grouped ants decreased more rapidly than on isolated individuals. Allo-grooming behavior appears to be important in removing the conidia on the surface of RIFA. Individuals help fungus exposed ants by performing intensive grooming behaviors, which either risk infecting themselves or get them immunized as social immunity. We show evidence that contacting with fungus exposed ants would decrease susceptibility of nestmates to the fungus. All these results indicate that RIFA benefit from grooming behavior to fight against the fungal pathogens. Future advances in biological control of RIFA with entomopathogenic fungi are also discussed.