Symbiosis of nematodes, fungi and beetle vectors

Summary The wood-inhabiting nematodes of the family Aphelenchoididae are part of a transmission disease association of a beetle vector and pathogenic fungi that causes economic damage to forestry worldwide. In this review the bark beetle association is analysed as the tripartite symbiotic community and a part of the wood-colonising biome that includes also the infected tree community. In the biome besides of the phoresy of blue-stain fungi and nematodes by their beetle hosts, there are mutualistic interactions of fungi and bark beetles, and the parasitic relationships of nematodes with the xylobiont fungi and plant host. Using the strength of the symbiotic adaptations of partners and phylogenetic data, a hypothesis has been put forward about the origin of the symbiotic system from two ancestral microbiomes (nematode-fungus-plant and vector-fungus-plant) with three symbionts in the final biome. For the relatively little-studied relationships of the entomochoric nematodes and fungi, two experimental methods are proposed to study the questions: i ) whether the propagative generations of beetle vectored nematodes feed preferably on fungi inoculated by the same bark beetle; ii ) whether some pathogenic xylobiont fungi may be obligatory vectored by the entomochoric nematodes.