Presence of weed fungus in a non‐social beetle–fungus cultivation mutualism

1. Farming by non‐human organisms has arisen independently in several animal lineages, allowing them to survive on food sources that are otherwise difficult to access. However, agricultural gardens are prone to invasion by parasites that overgrow cultivars in the absence of host animals. The presence of garden parasites and associated host adaptations are well studied in advanced fungal agriculture practised by social insects (ants, termites, and ambrosia beetles), but the impact of garden parasites in more primitive forms of agriculture is poorly known. The aim of the present study was to report the presence of weed fungi in fungal gardens of the non‐social lizard beetle D oubledaya bucculenta L ewis ( C oleoptera: E rotylidae: L anguriinae), which cultivates the yeast W ickerhamomyces anomalus ( E.C. H ansen) K urtzman, R obnett & B as.‐ P owers in the internodes of recently dead bamboo culms. 2. The filamentous fungi A rthrinium spp., F usarium spp., and an unidentified species were isolated from the inner wall and insect‐made wall debris of bamboo internodes inhabited by the beetle. 3. When cultured together with the yeast in the absence of host larvae, A rthrinium sp.1 outcompeted the yeast, suggesting that this filamentous fungus can invade yeast gardens but is normally suppressed under natural conditions. 4. Rearing experiments showed that beetle larvae grew faster when grown on yeast cultures than when fed only A rthrinium sp.1. 5. These results suggest that A rthrinium sp.1 acts as a weed in the fungal gardens of D . bucculenta , inhibiting both growth of the beetle larvae and proliferation of the beneficial yeast.