Chemical Signals of Vector Beetle Facilitate the Prevalence of a Native Fungus and the Invasive Pinewood Nematode

In China, the invasive Bursaphelenchus xylophilus, the vector Monochamus alternatus beetle, and associated fungi exhibit a symbiotic relationship causing serious losses to pine forests. Although this complex system has been intensively investigated, the role of vector beetles on the development of associated fungi and their indirect contribution to the prevalence of pinewood nematode (PWN) is yet unknown. Here, three of the highly prevalent fungal species, viz., Sporothrix sp. 1, Ophiostoma ips, and Sporothrix sp. 2 were isolated from beetle chambers in diseased trees in Guangdong province, southeast China. Pairwise cultivation of isolated fungi demonstrated the dominance of Sporothrix sp. 1 over O. ips and Sporothrix sp. 2. On the other hand, two fatty acid ethyl esters (FAEE), ethyl palmitate (EP) and ethyl linoleate (EL), isolated from the body surface of the vector beetle enhanced the growth of Sporothrix sp. 1. When PWN were cultured on Sporothrix sp. 1, the fecundity and the body length were increased significantly as compared with when cultured on O. ips and Sporothrix sp. 1. Our results suggest that the vector beetles promote Sporothrix sp. 1 to occupy more niches by rapid growth and spread, which in turn better support PWN population, hence facilitate PWN pathogenicity in the invasive regions.