Vectors of Dutch Elm Disease in Northern Europe.

Abstract

Simple SummaryDutch elm disease (DED) has been killing elms for more than a century in northern Europe; the trees’ health status has worsened substantially in recent decades. Elm bark beetles Scolytus spp. are vectors of DED. Our aim was to estimate the distribution range of elm bark beetles and to detect potential new vectors of DED agents in northern Europe. Beetles were caught with bottle traps and manually. Then DNA from each specimen was extracted and analysed by the third generation sequencing method. DED agents were detected on the following bark beetles for Europe: Scolytus scolytus, S. triarmatus, S. multistriatus, S. laevis, and on new vectors: Xyleborus dispar and Xyleborinus saxesenii. The spread of Scolytus triarmatus, S. multistriatus and Xyleborinus saxesenii has been remarkable for the last two decades, and S. triarmatus and X. saxesenii are relatively recent newcomers in the northern Baltics. The problem is that the more vectoring beetles there are, the faster spread of Dutch elm disease from tree to tree.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.