Ant-produced chemicals are not responsible for the specificity of their Ophiocordyceps fungal pathogens

In this study, we investigated the effects of exocrine glandular extracts (mandibular glands, post-pharygeal glands) and cuticular extracts of two species of formicine ant Polyrhachis furcata and Colobopsis saundersi on spore germination of two species of host-specific, entomopathogenic fungi Ophiocordyceps unilateralis (Ophiocordyceps polyrhachis-furcata and Ophiocordyceps camponoti-saundersi). Extracts from the two ant species inhibited the germination of O. polyrhachis-furcata, but did not affect the germination of O. camponoti-saundersi, invalidating the hypothesis of specificity mediated by exocrine glands. We also showed that metapleural gland extracts-well known for their anti-microbial activities-from ants not targeted by O. unilateralis, inhibited spore germination. Finally, we tested the effect of the glands of the two formicine ants on Beauveria bassiana, a widespread pathogen of insects. Germination of B. bassiana was stimulated by most extracts, suggesting that insect chemicals are used as signals for germination by this fungus. The chemical characterisation of ant glandular extracts was also performed.