Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Agric. Handbk. 706. Washington, D.C.: U.S. Department of Agriculture, Forest Service. 735 p
Elm. All native and introduced species of elm as well as Japanese zelkova (USDA FS 1985).
Introduced from Europe, presumably in either burl elm logs sent to veneer plants or in elm crates used to carry cargo (Whitten 1960). First recorded near Boston, Massachusetts, in 1909 and since reported from every state except Alaska and Hawaii; occurs across southern Canada from Nova Scotia to British Columbia (Schreiber and Peacock 1979, USDA FS 1985, Wood 1982).
Small bark beetle with shiny upper surface; pronotum nearly black, elytra dark reddish brown, length 1.9 to 3.1 mm (Blackman 1934, USDA FS 1985, Whitten 1960, Wood 1982). Head of male flattened in front between eyes; that of female, convex. Antennae clubbed at extremity. Face covered with many, fine, long, incurved, yellow hairs, except near median line. Pronotum slightly wider than long. Elytra slightly wider than pronotum; about 1.3 times as long as wide. Posterior underside of abdomen concave, second sternite nearly vertical and armed with noticeable stout spine projecting from anterior margin
Small, globular, shiny, pearly white.
White, legless grub with brown head, C-shaped, 2.8 to 3.2 mm long.
White initially, gradually darkens, wings folded under abdomen, about 3 mm long.
Larvae overwinter in pupal chambers in bark (Schreiber and Peacock 1979, USDA FS 1985, Whitten 1960). They pupate in spring, and adults emerge through "shot holes"; they chew through the bark at about the time the first elm leaves fully expand (late March to early June, depending on latitude). Emerging adults fly directly to weakened or diseased elms to breed in the inner bark or to healthy elms to feed on the bark in the crotches of 2- to 4-year-old twigs. Beetles that emerge from trees with Dutch elm disease become contaminated with the fungus Ceratocytis ulmi (Buisman) C. Moreau and in feeding often transmit it to healthy trees. Breeding attacks typically begin in weakened trees. Females initiate the attack and release an aggregating pheromone that attracts both sexes to the breeding site. After mating near entrance holes in the bark, females bore egg galleries in the inner bark 2.5 to 8 mm long and parallel with the grain. Eggs are deposited in closely spaced niches along the sides of the egg gallery. Larvae feed in the inner bark and surface of the wood. Their parallel galleries radiate at right angles to the egg gallery, but larvae often turn and follow the wood grain as they mature. Larval galleries are 8 to 20 cm long. Pupation occurs largely in the bark, and adults emerge through individually excavated holes. Development from egg to adult during summer is about 6 weeks. This bark beetle has two generations per year in the Midwest; three generations per year are common in the South.
Injury and damage
By midsummer, many healthy elms that experienced twig-crotch feeding by newly emerged beetles will develop symptoms of Dutch elm disease: wilting, drying, yellowing, and browning of foliage followed usually by defoliation and death. Symptoms can occur on scattered branches, or the entire crown may wilt and die suddenly. In the inner bark and etched into the surface of the sapwood are the characteristic gallery patterns of adults and larvae. Egg galleries are straight and run vertically along the wood grain. Closely spaced larval galleries radiate perpendicularly from both sides of the egg gallery but then turn and follow the wood grain. Galleries often overlap and frequently girdle the tree. Bark appears perforated by numerous small shot-sized emergence holes, 0.7 to 1.1 mm in diameter. This pest is the principal vector of Dutch elm disease in the United States and annually contributes to the dearth of thousands of valuable street, shade, and park trees (Schreiber and Peacock 1979, Shenefelt and Benjamin 1955). The United States Government has spent huge sums of money to control this beetle (USDA FS 1985).
Eight species of hymenopterous parasites have been identified (Bushing 1965, Krombein and others 1979). Four disease-causing pathogens-including three entomogenous bacteria (Aceobacter scolyti Presson, Escherichia klebsiellaeformis Presson, Serratia marsescens Bizio (Vago 1963) and one fungus, Beauveria bassiana (Balsamo) Vuillemin-have been reported. Studies show that 92% of overwintering larvae in damp habitats are killed by B. bassiana, but only 4% mortality occurs in dry habitats (Madelin 1963). Low temperatures and overcrowding of broods in the bark have also been reported as natural controls (Schenefelt and Benjamin 1955). Losses caused by this pest and the accompanying Dutch elm disease can be minimized by concerted community efforts to (1) reduce beetle populations by eliminating breeding materials through sanitation and tree care, (2) protect healthy trees with insectididal sprays, (3) prevent underground disease transmission by destroying natural root grafts between diseased and healthy tree, and (4) plant trees that are resistant to Dutch elm disease (Schrieber and Peacock 1979). Pheromones can be used to detect and monitor beetle populations and to time chemical controls (Birch and others 1981).
Birch, Martin C., Timothy D. Paine, and Jeffrey C. Miller. 1981. Effectiveness of pheromone mass-trapping of the smaller European elm bark beetle. California Agriculture. 35(1,2):6,8. Blackman, M.W. 1934. A revisional study of the genus Scolytus Geoffrey (Eccoptogaster Herbst) in North America. Bull. 431. Washington, D.C.: U.S. Department of Agriculture. 30 p. Bushing, Richard W. 1965. A synoptic list of parasites of Scolytidae (Coleoptera) in North America north of Mexico. Canadian Entomologist. 97(5): 449-492. Krombein, Karl V., Paul D. Hurd, Jr., David R. Smith, and B.D. Burks. 1979. Catalog of Hymenoptera in America north of Mexico: Vol. 1, Symphyta and Apocrita (Parasitica). Washington, D.C.: Smithsonian Institution Press. 1,198 p. Madelin, M.F. 1963. Diseases caused by hyphomycetous fungi. In: Steinhaus, E.A., ed. Insect pathology; Vol. 2. New York: Academic Press: 233-271. Schreiber, Lawrence R., and John W. Peacock. 1979. Dutch elm disease and its control. Agric. Info. Bull. 193. Washington, D.C.: U.S. Department of Agriculture, Science and Education Administration, 13 p. Shenefelt, Roy D., and Daniel M. Benjamin. 1955. Insects of Wisconsin forests. Circ. 500. Madison, WI: University of Wisconsin, Agricultural Extension Service. 110 p. U.S. Department of Agriculture, Forest Service. 1985. Insects of eastern forests. Misc. Publ. 1426. Washington, D.C. 608 p. Vago, C. 1963. Predispositions and interrelations in insect diseases. In: Steinhaus, E.A., ed. Insect pathology: Vol 1. New York: Academic Press: 339-380. Whitten, R. R. 1960. Elm bark beetles. Leafl. 185, rev. Washington, D.C.: Department of Agriculture. 8 p. Wood, Stephen L. 1982. The bark and ambrosia beetles of North and Central America (Coleoptera: Scolytidae), a taxonomic monograph. Great Basin Naturalist. Memoir 6. 1,359 p.
This beetle is the prime vector of the Dutch elm disease fungus which has destroyed millions of American elms since its introduction into the United States. The beetle attacks all native and introduced species of elms.
Identifying the Insect
Adults are reddish-brown beetles about 1/4 inch (3 mm) long. The underside of the posterior is concave and armed with a prominent projection or spine on the undersurface of the abdomen. The larvae are typical, white or cream-colored, legless grubs, about the same size as adults.
Identifying the Injury
Beetles excavate a 1 to 2 inch (25 to 50 mm) straight egg gallery parallel with the wood grain. Larval mines are roughly perpendicular to the egg gallery. The result is a design resembling a long-legged centipede on the inner bark and wood surface.
Symptoms of the disease are described under "Dutch Elm Disease" in this booklet.
Smaller European elm bark beetles overwinter as larvae under the bark and develop into adults in the spring, emerging after the leaves expand. Adults feed at twig crotches of healthy elms, infecting the tree with Dutch elm disease. Then they fly on to other elms for breeding. These attacked trees have usually been weakened by drought, disease, or other stress factors.
After boring through the bark, the beetles excavate their egg galleries, grooving the inner bark and wood surface in the process. When larvae are full-grown, they construct pupal cells at the end of their larval mines. New adults emerge by boring directly through the bark, leaving it peppered with tiny "shot holes." There are two generations annually.
The most effective method of reducing losses is probably through removal of dead and dying elms and the pruning of dead and dying limbs. Several chemical insecticides may be applied as preventative sprays or to kill beetles before they spread to uninfested trees.
Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html