Potential Dutch elm disease vector beetle species were caught with pheromone bottle traps and handpicked in 2019: in total, seven species and 261 specimens were collected. The most common was Scolytus triarmatus, but by percent, the incidence of Ophiostoma novo-ulmi was highest in Scolytus scolytus, followed by Xyleborinus saxesenii and S. triarmatus. We analysed the beetles’ DNA using PacBio sequencing to determine vector beetles of Ophiostoma novo-ulmi. Ophiostoma novo-ulmi was found on six out of seven analysed beetle species: Scolytus scolytus, S. triarmatus, S. multistriatus, S. laevis, Xyleborinus saxesenii and Xyleborus dispar. The last two beetles were detected as vectors for Ophiostoma novo-ulmi for the first time. Previous knowledge on the spread of beetles is discussed.

Dutch elm disease (DED), caused by the pathogenic ascomycete Ophiostoma novo-ulmi, has devastated natural elm (Ulmus spp.) populations in Europe and North America. Elm species vary in their susceptibility to this vascular disease, which may partly reflect differences in their associated mycobiomes. To investigate the diversity and composition of fungal endophyte communities in relation to host genotype, health status, and environment, we analyzed twig-associated fungi in symptomatic and asymptomatic individuals of highly susceptible U. glabra, less susceptible U. laevis, and hybrid elms growing in Estonia and Russia. Fungal communities were analyzed using PacBio long-read amplicon sequencing of the ITS1-5.8S-ITS2 gene region. Tree species exhibited distinct fungal community profiles. Ophiostoma novo-ulmi was detected exclusively in symptomatic trees and was dominant in U. glabra; it was absent in symptomatic hybrid elms. In contrast, the canker-associated pathogen Sphaeropsis ulmicola occurred in both symptomatic and asymptomatic trees, was dominant in symptomatic U. laevis, and common in symptomatic and healthy U. glabra, though less prevalent in symptomatic hybrid elms. Remarkably, S. ulmicola was associated with the highest level of damage in U. laevis while being present also in hybrid elms. While O. novo-ulmi’s presence did not affect overall fungal richness, S. ulmicola was linked to higher fungal diversity. Additionally, fungal species richness was significantly greater in urban compared to rural environments. This was the first comparable analysis of fungal diversity and composition on three different Ulmus species shoots.

This review provides an overview of and describes the current situation of Dutch elm disease (DED), which is one of the most devastating diseases for elms worldwide and in Estonia. It is known that in Estonia DED’s agent Ophiostoma ulmi has been damaging elms since the 1930s. Today a new species Ophiostoma novo-ulmi is considered to be an agent of DED. Since 2013 the current epidemic has been recorded in most of the counties of Estonia. The both known DED agents, Ophiostoma novo-ulmi subsp. novo-ulmi and O. novo-ulmi subsp. americana were molecularly detected on Ulmus spp. Additionally, one hybrid pathogen of the subspecies ( americana x novo-ulmi ) was identified in northern Estonia. Also, the health status of elms and the potential vector agents of the pathogen are discussed and recommendations for disease management are provided.