Dutch elm disease

Dutch elm disease (DED) is caused by a member of the sac fungi (Ascomycota) affecting elm trees, and is spread by elm bark beetles. Believed to be originally native to Asia, the disease was accidentally introduced into America, Europe, and New Zealand. In these regions it has devastated native populations of elms that did not have resistance to the disease. The name "Dutch elm disease" refers to its identification in 1921 and later in the Netherlands by Dutch phytopathologists Bea Schwarz and Christine Buisman, who both worked with professor Johanna Westerdijk. The disease affects species in the genera Ulmus and Zelkova, therefore it is not specific to the Dutch elm hybrid. Dutch elm disease (DED) is caused by ascomycete microfungi. Three species are now recognized: Ophiostoma ulmi, which afflicted Europe from 1910, reaching North America on imported timber in 1928. Ophiostoma himal-ulmi, a species endemic to the western Himalaya. Ophiostoma novo-ulmi, an extremely virulent species from Japan which was first described in Europe and North America in the 1940s and has devastated elms in both continents since the late 1960s. DED is spread in North America by three species of bark beetles (Family: Curculionidae, Subfamily: Scolytinae): The native elm bark beetle, Hylurgopinus rufipes. The smaller European elm bark beetle, Scolytus multistriatus. The banded elm bark beetle, Scolytus schevyrewi. In Europe, while S. multistriatus still acts as a vector for infection, it is much less effective than the large elm bark beetle, S. scolytus. H. rufipes can be a vector for the disease, but is inefficient compared to the other vectors. S. schevyrewi was found in 2003 in Colorado and Utah. Other reported DED vectors include Scolytus sulcifrons, S. pygmaeus, S. laevis, Pteleobius vittatus and Р. kraatzi. Other elm bark beetle species are also likely vectors. 'Field resistance' is an umbrella term covering the various factors by which some elms avoid infection in the first place, rather than survive it.