European Elm Bark Beetle

Scolytus multistriatus — the European elm bark beetle — is one of the most economically important INVASIVE FOREST PEST insects in North America and the primary VECTOR of DUTCH ELM DISEASE. The species is native to Europe but was accidentally introduced to North America in the 1930s (almost certainly via imported elm logs from Europe), and has spread aggressively across NA over the past 90 years. Adults are 2-3 mm long, dark reddish-brown, with the species' diagnostic features: small body size, multiply-striated elytra (the elytra have many fine longitudinal ridges — source of the species name 'multistriatus'), and short antennae adapted for the species' bark-tunneling lifestyle. The species' major significance comes from VECTORING DUTCH ELM DISEASE. Dutch elm disease is a deadly fungal disease of elm trees caused by the fungus OPHIOSTOMA NOVO-ULMI (originally also called Ophiostoma ulmi — there are two related Ophiostoma species causing disease, with O. novo-ulmi being the more aggressive form responsible for most modern disease). The fungus invades the water-conducting xylem vessels of elm trees, blocks water transport from roots to crown, and kills the host tree (often within a single growing season for vulnerable American elm hosts). The disease is transmitted from tree to tree by elm bark beetles — adult Scolytus multistriatus beetles emerge from infected dead elm trees carrying fungal spores in body crevices, fly to feed on twig crotches of healthy elm trees, and transmit the spores to the new host tree during feeding. The fungus then invades the xylem and kills the new host. Dutch elm disease has caused ONE OF THE MOST CATASTROPHIC TREE-DISEASE EPIDEMICS IN NORTH AMERICAN HISTORY — TENS OF MILLIONS of AMERICAN ELM TREES (Ulmus americana) have died across NA since the disease arrived in the 1930s. The American elm was historically one of the most-planted street trees in NA cities (especially Chicago, New York, Boston, and other major Northeast and Midwest cities), with elm-lined streets a defining visual feature of urban American landscape. The Dutch elm disease epidemic destroyed essentially all mature American elms in most NA cities by the 1980s, transforming the appearance of NA urban landscapes and dramatically altering eastern NA forest composition. The species is the focus of major international forest entomology research and is featured in essentially every modern textbook discussion of insect-vectored plant diseases. Modern control efforts include: aggressive sanitation (rapid removal and destruction of infected elm trees to remove beetle breeding habitat), insecticide applications to bark of high-value elms, fungicide injections directly into elm trunks, breeding for disease-resistant elm varieties (modern Dutch-elm-disease-resistant cultivars including 'Princeton', 'Valley Forge', and 'Liberty' elms have been developed and are increasingly planted), and quarantine restrictions on elm log movement.