The evolution of fungus farming in ship‐timber beetles (Coleoptera: Lymexyloidea)

Ambrosia beetles farm fungi as a food source in tunnels within wood. Obligate fungus farming in ambrosia beetles has evolved more than 10 times independently and is primarily studied in the curculionid subfamilies Scolytinae and Platypodinae. In contrast, ambrosia beetles of the superfamily Lymexyloidea are sparsely studied, leaving the occurrence of fungus farming and its evolutionary history poorly understood. Larvae of the genus Elateroides Schaeffer cultivate mutualistic Alloascoidea Kurtzman & Robnett yeasts for nutrition within their tunnels in dead wood. These mutualistic fungi are vertically transmitted via specialized pouches, known as mycetangia, located at the ovipositor of adult females. This study aims to determine the origin of obligate fungus farming in Lymexyloidea. We reconstructed molecular phylogenies of the superfamily using two datasets: (1) a dataset with mitochondrial genome sequences from 47 taxa spanning the entire Lymexyloidea and (2) a phylogenomic dataset of 827 BUSCO orthologs from five representative lymexyloid taxa and four outgroups. We used micro‐computed tomography (micro‐CT) to detect mycetangia on the ovipositors of 13 extant lymexyloid taxa and on the extinct species Elateroides helmi sp. nov., preserved in Baltic amber. The discovery of E. helmi documents the presence of the Hylecoetinae in the Eocene. By integrating mycetangia presence/absence data with our phylogeny, we conclude that obligate fungiculture in the Lymexyloidea likely originated once within the subfamily Hylecoetinae.