BARK BEETLES Integrated Pest Management for Home Gardeners and Landscape Professionals Bark beetles, family Scolytidae, are California now has 20 invasive spe- common pests of conifers (such as cies of bark beetles, of which 10 spe- pines) and some attack broadleaf trees. cies have been discovered since 2002. Over 600 species occur in the United The biology of these new invaders is States and Canada with approximately poorly understood. For more informa- 200 in California alone. The most com- tion on these new species, including mon species infesting pines in urban illustrations to help you identify them, (actual size) landscapes and at the wildland-urban see the USDA Forest Service pamphlet, interface in California are the engraver Invasive Bark Beetles, in References. beetles, the red turpentine beetle, and the western pine beetle (See Table 1 Other common wood-boring pests in Figure 1. Adult western pine beetle. for scientific names). In high elevation landscape trees and shrubs include landscapes, such as the Tahoe Basin clearwing moths, roundheaded area or the San Bernardino Mountains, borers, and flatheaded borers. Cer- the Jeffrey pine beetle and mountain tain wood borers survive the milling Identifying Bark Beetles by their Damage pine beetle are also frequent pests process and may emerge from wood and Signs. The species of tree attacked of pines. Two recently invasive spe- in structures or furniture including and the location of damage on the tree cies, the Mediterranean pine engraver some roundheaded and flatheaded help in identifying the bark beetle spe- and the redhaired pine bark beetle, borers and woodwasps. Others colo- cies present (Table 1). On large pines, colonize various Mediterranean pines, nize wood after it has been placed for example, engraver beetles usually which are widely planted in and in structures, such as carpenter ants, attack trees near the top, whereas red around the Los Angeles Basin and the carpenter bees, powderpost beetles, turpentine beetles attack the lower Central Valley. and termites. For more information on portion of the trunk. They can even these other borers, see the Pest Notes colonize near the root collar and Cedar and cypress bark beetles attack listed in References. exposed roots and continue to mine arborvitae, cypress, false cypress, ju- under the bark below ground on the nipers, and redwoods. The fir engraver IDENTIFICATION large roots. Engraver beetles are dark brown, cylindrical, and have a scoop- attacks white and red fir at high eleva- Bark beetle adults are small, cylindri- like depression at the end of the abdo- tion locations. Oak bark and ambrosia cal, hard-bodied insects about the men that is lined with stout spines. beetles attack oaks and certain other size of a grain of rice. Most species Their presence is indicated by piles broadleaf trees including California are dark red, brown, or black. When of dry boring dust pushed out on the buckeye and tanbark oak. A long-time viewed under magnification, their bark surface. Red turpentine beetles antennae are visibly elbowed with the (naturalized) invasive bark beetle are larger than engraver beetles, red- outer segments enlarged and clublike called the shothole borer attacks dam- dish brown, and have a rounded tip to aged branches and trunks of many (Fig. 1). When viewed from above, the the abdomen (Fig. 1). Their presence broadleaved tree species, including head is partly or completely hidden by is indicated by large, pinkish brown fruit trees and English laurel. Two the pronotum (the top of the body part to white pitch tubes (a mixture of pine other invasive species, the European behind the head). Bark beetles have sap and beetle boring dust that ap- elm bark beetle and the banded elm strong mandibles (jaws) for chewing. pears on the lower trunk, Fig. 2). bark beetle feed on elms and vector A buckshot pattern of holes is appar- Dutch elm disease fungus (Ophiostoma ent on the bark surface of infested Identifying Bark Beetles by their Galler- novo-ulmi). In its native habitat in Asia, branches or trunks where the new ies. Peeling off a portion of infested the banded elm bark beetle reportedly adults have emerged. Larvae of most bark to reveal the winding pattern of also feeds on certain non-elm tree species are off-white, robust, grublike, the beetle galleries (tunnels chewed species. and may have a dark brown head. by adults and larvae) is a good way to EST OTES Publication 7421 PUniversity of California N Agriculture and Natural Resources November 2008 November 2008 Bark Beetles Table 1. Bark Beetles Common in California Landscapes Species Trees affected Generations Comments per year Cedar and cypress bark arborvitae, cypress, 1 to 2 tunnels resemble centipede (Fig. 2) on wood surface beetles false cypress and the inner bark; adult feeds on and kills twigs; egg- (Phloeosinus species) (Chamaecyparis), laying female attracted to trunk of dead or dying trees junipers, and redwood Elm bark beetles elms 2 overwinter as fully grown larvae in bark; shot holes in (Scolytus multistriatus, bark indicate damage; lay eggs in limbs and trunk of Scolytus schevyrewi1) injured, weakened, or recently cut elms; spread Dutch elm disease fungi Engraver beetles pine 1 to 5 overwinter as adults; often make wishbone-shaped (Ips emarginatus, tunnels; attack pines near the top of the stem Ips mexicanus, Ips paraconfusus, Ips pini, Ips plastographus) Fir engraver white and red fir 1 to 2 overwinter as larvae; adults excavate deep and long, (Scolytus ventralis) two-armed galleries across the grain of the sapwood Jeffrey pine beetle Jeffrey pine 1 to 2 attack midtrunk of large trees, from 5 to about 30 ft; (Dendroctonus jeffreyi) make long J-shaped galleries, overwinter as larvae in the inner bark Mediterranean pine engraver pine 3 to 4 infest trunk and large limbs of Mediterranean pines, (Orthotomicus [formerly Ips] especially Aleppo pine (Pinus halepensis) and Italian erosus)1 stone pine (Pinus pinea) Mountain pine beetle pine, frequently on 1 to 2 attack midtrunk of large trees, from 5 to about 30 ft; (Dendroctonus ponderosae) lodgepole and sugar makes long J-shaped galleries, overwinter as larvae in pine the inner bark Oak ambrosia beetles buckeye, oaks, and 2 or more overwinter beneath bark; bleeding, frothy, bubbling (Monarthrum species); tanbark oak holes with boring dust indicate damage; attack Oak bark beetles stressed trees (Pseudopityophthorus species) Redhaired pine bark beetle pine 2 to 3 believed to prefer roots and lower trunk of declining (Hylurgus ligniperda)1 Aleppo pine and Canary Island pine (Pinus canariensis) Red turpentine beetle pines, rarely in larch, 0.5 to 2 attack lowest 2 to 8 ft. of trunk and the large roots; (Dendroctonus valens) spruce, or white fir pitch tubes appear on bark; overwinter as adults and larvae; rarely kill trees Shothole borer English laurel, fruit 2 or more infestation indicated by gumming of woody parts, (Scolytus rugulosus) trees, hawthorn, and appearance of boring dust, or twig dieback; remove other woody plants and destroy infested parts Twig beetles pine, walnut 2 or more attack lateral shoots and twigs, can mine the pith; (Pityophthorus carmeli, pine species are associated with pitch canker disease Pityophthorus juglandis, transmission; on walnut Pityophthorus juglandis Pityophthorus nitidulus, is associated with thousand cankers disease Pityophthorus setosus) transmission Western pine beetle Coulter and 2 to 4 attack midtrunk, then spreads up and down; larvae (Dendroctonus brevicomis) ponderosa pines feed on inner bark, complete development in outer bark; attack in conjunction with other pests 1 Recently introduced species whose biology and potential impact in California is poorly understood. ◆ 2 of 7 ◆ November 2008 Bark Beetles and again in late summer to early fall. After emergence, adults may re-infest the same tree or, in most cases, dis- perse to attack susceptible trees else- where (Fig. 3). Most bark beetle species have two or more generations a year in California, depending on temperature. At warmer locations (such as lower elevations away from the coast), the season of attack is usually longer and beetles have more generations per year in comparison with cooler coastal or high-elevation locations. DAMAGE AND SIGNS Bark beetles mine the inner bark (the phloem-cambial region) on twigs, branches, or trunks of trees and shrubs. This activity often starts a flow of tree sap in conifers, but some- times even in hardwoods like elm and walnut. The sap flow (pitch tube) is accompanied by the sawdustlike frass created by the beetles. Frass accumu- lates in bark crevices or may drop and be visible on the ground or in spider webs. Small emergence holes in the bark are a good indication that bark beetles were present. Removal of the bark with the emergence holes often reveals dead and degraded inner bark Figure 2. Signs of bark beetle activity include pitch tubes on the bark surface and sometimes new adult beetles that (lower left), egg galleries (tunnels), and larval mines beneath the bark. Galleries have not yet emerged. Bark beetles filled with boring dust (frass) are shown in black, whereas open portions of gal- frequently attack trees weakened by leries are white. drought, disease, injuries, or other fac- identify individual beetle species. Red in mines much like the western pine tors that may stress the tree. Bark bee- turpentine beetle and western pine beetle. Galleries chewed by larvae tles can contribute to the decline and beetle adults usually pack about 60% of all species are packed with frass eventual death of trees, however only of their egg-laying galleries with a (Fig. 2). a few aggressive species are known to sawdustlike boring dust called “frass,” be the sole cause of tree mortality. whereas engraver beetles maintain LIFE CYCLE In addition to attacking larger limbs, clean, open adult galleries.