Eastern ash bark beetle - Hylesinus aculeatus (Say)
[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.]
Hosts. - Ash. White and green ash, but other ash species also probably serve as hosts (Beal and Massey 1945, Blackman 1922, Chamberlin 1939).
Range. - Eastern United States west to the Rocky Mountains and eastern Canada west to Manitoba (Blackman 1922, Furniss and Carolin 1977, Ives and Wong 1988).
Adult. - Small, elongate, cylindrical bark beetle, 2.2 to 3.4 mm long (Blatchley and Leng 1916, Ives and Wong 1988, USDA FS 1985). Dark brown; distinct light and dark patterns occur due to dense covering of flattened, whitish gray scales (Blackman 1922). Light scales on pronotum outline a diamond-shaped patch of dark, reddish brown scales. Brown and gray scales on elytra form a variable herringbone pattern. Elytra slightly wider than pronotum and serrate along anterior margin. Rear of elytra convex and gradually sloped (Beal and Massey 1945).
Larva. - White with brown mandibles, legless, C-shaped; thoracic segments moderately larger than abdominal segments.
Biology. - Adults emerge from hibernation as early as late March in Mississippi (Blackman 1922) but as late as May or June in the northern range (Ives and Wong 1988). Adults fly to limbs and trunks of seriously weakened, dying, and felled trees to reproduce (USDA FS 1985). Females make large transverse egg galleries beneath the bark and deposit eggs singly in niches on opposite sides of the gallery. Larvae tunnel perpendicular to the egg gallery with the wood grain and pupate at the ends of the feeding galleries in oval cells. Adult and larval galleries and pupal cells deeply etch the sapwood surface and inner bark (Chamberlin 1939, USDA FS 1985). Newly formed adults rarely disturb the beautiful design of the galleries because they burrow straight out from their pupal cells to the bark surface to emerge. In fall, adults construct short feeding tunnels in the bark of living or recently felled trees and overwinter (Beal and Massey 1945). This bark beetle has one generation per year in Minnesota, with new adults leaving hosts in midsummer to seek winter hibernation sites (Dodge 1938); two generations occur in North Carolina (Beal and Massey 1945). In Mississippi, beetles develop from egg to adult in 2 to 2.5 months; thus, three generations seem possible (Blackman 1922).
Injury and damage. - Bark on susceptible trees and fresh-cut logs may be peppered with small round entrance holes. Fine frass may accumulate in bark crevices. Removing bark reveals typical galleries and white tunneling larvae. The prominent egg galleries are characterized as biramous and transverse, with two arms connected by a very short, slightly enlarged tunnel below the entrance hole, which serves as a turning niche and nuptial chamber (Beal and Massey 1945, Blackman 1922). Egg galleries range from 2 to 6 cm long. Larval galleries are packed with frass and radiate outward nearly perpendicular from the transverse egg galleries. Larval engravings are further characterized as longitudinal, regularly and closely space, and short and uniform (2 to 5 cm). Few other bark beetles produce more uniform galleries (Chamberlin 1939). Beetles leave many tiny round exit holes about 1 mm in diameter in the bark. When populations are high, hibernating niches can be found in the inner bark of healthy trees. Hibernating niches often extend through the bark to the cambium and cause small defects in the wood. Although the beetle can hasten the death of trees weakened by fire, disease, injury, and other stresses, it is seldom important from an economic standpoint (Beal and Massey 1945). Occasionally, it is an economic pest to producers of “rustic” (bark still on) ash products (USDA FS 1985).
Control. - Six species of parasites have been listed (Bushing 1965). In New Jersey studies, 32% of the larvae were killed by a hymenopterous parasite—Coeloides scolytivorus (Cresson) (Hoffmann 1938). In another study in Mississippi, parasitism by an unidentified wasp ran as high as 90% (Blackman 1922). A clerid beetle—Enoclerus quadrigutattus Olivier—sometimes destroys large numbers of beetles. Direct controls are rarely warranted but, should they be necessary, felling and debarking infested trees and limbs before broods emerge control the insect (Beal and Massey 1945). Logs intended for “rustic” uses should be promptly removed from woodlands and stored in beetle-free areas or sprayed to prevent infestation.
Beal, James A., and Calvin L. Massey. 1945. Bark beetles and ambrosia beetles (Coleoptera: Scolytidae). Bull. 10. Durham, NC: Duke University, School of Forestry. 178 p.
Blackman, M.W. 1922. Mississippi bark beetles. Tech. Bull. 11. Starkville, MS: Mississippi Agricultural Experiment Station. 130 p.
Blatchley, W.S., and C.S. Leng. 1916. Rhynchophora or weevils of north eastern America. Indianapolis: Nature Publishing Co. 682 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.
Chamberlin, W. J. 1939. The bark and timber beetles of North America north of Mexico. Corvalis, OR: Oregon State College Cooperative Association. 513 p.
Dodge, Harold Rodney. 1938. The bark beetles of Minnesota (Coleoptera: Scolytidae). Tech. Bull. 132. St. Paul, MN: Minnesota Agricultural Experiment Station. 60 p.
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.
Hoffmann, Clarence H. 1938. Notes on Leperisinus aculeatus (Say) and its parasites (Coleoptera: Scolytidae). Journal of Economic Entomology. 31(1):118-119.
Ives, W.G.H., and H.R. Wong. 1988. Tree and shrub insects of the Prairie Provinces. Edmonton, AB: Canadian Forestry Service, Northern Forestry Centre; Information Report NOR-X-292. 327 p.
U.S. Department of Agriculture, Forest Service. 1985. Insects of eastern forests. Misc. Publ. 1426. Washington, DC. 608 p.
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