Native Elm Bark Beetle - Hylurgopinus rufipes (Eichhoff)
[From: 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.]
Host. - Elm. Elm species are the major hosts, but also attacks basswood, ash, and wild cherry (USDA FS 1985).
Range. - Throughout the eastern United States north of Alabama and Mississippi (USDA FS 1985) west to Nebraska and North Dakota (Furniss and Carolin 1977); in Canada, from New Brunswick to Manitoba (Bright 1976).
Description. -
Adult. - Brownish black bark beetle, sparsely clothed with stiff, short, yellow hairs, and measuring 2.0 to 3.5 mm long (Bright 1976, USDA FS 1985). Head convex, thickly punctured, and barely visible from above. Antennal club almost twice as long as wide. Pronotum narrows toward front; entire surface densely punctured; posterior margin reddish. Longitudinal striae on elytra deep and contain deep punctures and erect bumps. Distinguished from S. multistriatus (Marsham) (also in elm) by color, shape, and the absence of a concave abdomen and prominent spine.
Egg. - Globular, shiny, white (Whitten 1960).
Larva. - Legless, C-shaped, fat, wrinkled, white with brown head, 3 to 5 mm long when mature.
Biology. - Adults emerge from mid-April to mid-May and fly to healthy elms to feed in the bark of large branches for brief periods (Hildahl and Jeffrey 1980, USDA FS 1985, Whitten 1960). After feeding, beetles fly to dying and recently dead trees for oviposition. They bore into bark crevices, or under bark scales, and tunnel to the inner bark where females construct egg galleries. Egg galleries extend horizontally across the grain and usually consist of two branches diverging from the point of penetration in the bark. Eggs are deposited along sides of the egg galleries, and developing larvae feed in closely spaced, parallel galleries that run mostly perpendicular to the egg galleries with the wood grain. Larvae pupate in small, oval-shaped cells in the bark at the ends of feeding tunnels. Larvae and adults overwinter in the bark. If the host has Dutch elm disease, emerging beetles will transmit fungal spores to healthy elms during the spring and fall adult feedings. There are two generations a year in the beetle’s southern range but only one to one-and-one-half generations in its northern range.
Injury and damage. - Red dust in bark fissures of living trees in spring and fall indicates overwintering beetles (Hildahl and Jeffrey 1980. Accurate identification is best made by examining the adult and larval gallery patterns found in the inner bark and slightly etched into the sapwood surface. The egg gallery of H. rufipes is horizontal or slightly inclined, distinguishing it from the egg gallery of S. multistriatus, which runs vertically with the wood grain. Larval galleries of H. rufipes run along both sides of the egg gallery perpendicular to the wood grain. Larvae, pupae, and callow adults may be found in small galleries and small cells. Emerging adults leave numerous small, round holes about 1 mm in diameter in the bark. Before Dutch elm disease was introduced in the United States, the native elm bark beetle was of little importance because it primarily attacked weakened, dying, and recently dead trees (McDaniel 1936). Now it is a major vector of Dutch elm disease, particularly in New England and Canada, where the species is more abundant than S. multistiatus (USDA FS 1985). Hylurgopinus rufipes populations can grow large during prolonged drought, when the beetles aggressively attack healthy trees (McDaniel 1936).
Control. - Ten species of hymenopterous parasites, predaceous birds, and disease are natural enemies (Bushing 1965, Whitten 1960). Woodpeckers capture many overwintering larvae and adults. Low winter temperatures and competition for food caused by larval overcrowding often cause high rates of mortality. Many communities emphasize prevention through good tree maintenance and strict sanitation as opposed to control (Hildahl and Jeffrey 1980). Infested and diseased elms should be removed and destroyed within 30 days of being diagnosed. Insecticidal sprays and injected fungicides have been used with some success in protecting valuable yard and street trees. However, for sanitation cutting and chemical treatment to be effective, the effort requires community-wide cooperation. Controls are rarely feasible in forests.
References
Bright, Donald E., Jr. 1976. The insects and arachnids of Canada: 2. The bark beetles of Canada and Alaska (Coleoptera: Scolytidae). Publ. 1576. Ottawa, Ontario: Canadian Department of Agriculture, Research Branch. 241 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.
Furniss, R.L., and V.M. Carolin. 1977. Western forest insects. Misc. Publ. 1339. Washington, D.C.: U.S. Department of Agriculture, Forest Service. 654 p.
Hildahl, Vern, and C.A. Jeffrey. 1980. The elm’s enemy. Winnipeg, Manitoba: Department of Natural Resources, Forestry Branch. 5 p.
McDaniel, E.I. 1936. Wood borers attacking deciduous trees and shrubs. Spec. Bull. 238, rev. East Lansing, MI: Michigan Agricultural Experiment Station. 52 p.
U.S. Department of Agriculture, Forest Service. 1985. Insects of eastern forests. Misc. Publ. 1426. Washington, D.C. 608 p.
Whitten, R. R. 1960. Elm bark beetles. Leafl. 185, rev. Washington, D.C.: Department of Agriculture. 8 p.
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