A termite fungistatic compound, mellein, inhibits entomopathogenic fungi but not egg-mimicking termite ball fungi

Abstract

Social insects form colonies with close relatives and face a high degree of risk of herd infection by the same pathogen. To prevent the intrusion and infection of pathogens and parasites, social insects have developed strong antimicrobial defenses. Although termites have been considered to produce a variety of antimicrobial compounds to prevent microbial infections, only a few antimicrobial compounds have been identified in termites. Here, we show that a new fungistatic component mellein is identified in a subterranean termite Reticulitermes speratus (Kolbe) (Isoptera: Rhinotermitidae). Using gas chromatography–mass spectrometry analysis, we identified mellein, an isocoumarin compound with a broad antimicrobial activity, from hexane extracts of soldiers and workers. In addition, antifungal test demonstrated that mellein has an inhibitory effect on the growth of entomopathogenic fungi (Metarhizium anisopliae and Beauveria bassiana), while no such effect on the termite-egg-mimicking fungus ‘termite ball’ (Fibularhizoctonia sp.) and its related species (Athelia rolfsii). These results suggest that R. speratus use mellein to confront the pathogenic fungi and that the termite-egg-mimicking fungus has a resistance against mellein. This study contributes to our better understanding of the diverse anti-pathogenic defense in termites.