In summer 2004 it was discovered that the Mediterranean pine engraver beetle (Orthotomicus erosus Wollaston) had become established in the Central Valley of California. The first detections occurred at two sites near Fresno (Lee et. al. 2005; Devorshak 2005). As of 2008, trapping and finds in cut logs of exotic pines that constitute important component of urban forests of the region showed that the beetle was present in 10 California counties, primarily in the southern Central Valley (Seybold and Downing, 2009). It is thought likely that the beetle was present in California three or more years before its detection in 2004 (Seybold and Downing, 2009).
Mode of Introduction
Introduction of the Mediterranean pine engraver beetle was not surprising, as it has been commonly associated with wood packaging. Between 1985 and 2000, inspectors found this beetle a total of 385 times in wood packaging. While the beetle was found in packaging from at least 19 different countries, it was most commonly found in crating holding imported tiles, marble, and granite (Haack, 2004). Before adoption of the international standard for wood packaging, shippers in Italy often failed to comply with APHIS’ 1995 regulations requiring that wood packaging be stripped of bark (Campbell & Schlarbaum, 2002).
This beetle is native to Europe, the Middle East, northern Africa, and China, and had previously been introduced to Fiji, Chile, South Africa and Swaziland (Lee et al. 2005; Devorshak 2005).
The Mediterranean pine engraver beetle is usually considered to be a secondary pest of pines. However, several experts consider the risk to North American pines to be significant for several reasons. First, the Mediterranean pine engraver beetle has caused significant damage to stressed pines on other continents (Seybold and Downing, 2009).
Second, the beetle has a wider host range than originally thought, including 11 native North American pines (eastern white – Pinus strobus, gray- P. sabineana, jack – P. banksiana, Jeffrey – P. jeffreyi, loblolly – P. taeda, Monterey – P. radiata, ponderosa – P. ponderosa, red – P. resinosa, Sierra, lodgepole – P. contorta, singleleaf pinyon, and sugar – P. lambertiana); as well as Douglas-fir – Pseudotsuga menziesii, black spruce – Picea mariana and white spruce- Picea glauca, & tamarack – Larix laricina. Relatively few progeny are produced on the non-pine hosts (Seybold and Downing, 2009).
Third, the Mediterranean pine beetle produces three to four generations per year in California, whereas it averages only two to three generations per year in its native range (Lee et al. 2007, 2009b; R.L. Penrose, CDFA, unpublished data). The result could be an even faster buildup of insect numbers.
When insect populations build up, the beetle is more likely to attack live trees (Lee et al. 2005; Devorshak 2005). In addition to direct feeding, the insect can transmit fungi, some of which might be pathogenic (Lee et al. 2005; Devorshak 2005). Documented examples include Ophiostoma ips (Rumb.) Nannf., causal agent of bluestain fungus; Leptographium lundbergii Lagerb. & Melin; Graphium pseudormiticum Mouton & Wingfield; and the pitch canker fungus, Fusarium circinatum Nirenberg and O’Donnell (Seybold and Downing, 2009).
The Mediterranean pine engraver beetle usually infests recently fallen trees and slash, but it also attacks stressed living trees. Scientists agree that the greatest economic damage would probably occur in pine plantations established in conditions under which the trees suffer stress, particularly drought. Native North American pine forests are often subject to drought and other stress factors – making them vulnerable to O. erosus (Eglitis, 2000; Devorshak 2005). Furthermore, the Mediterranean pine beetle can kill trees following various disturbances, including thinning followed by drought, forest thinning alone, and fire (Seybold and Downing 2009).
Areas with Mediterranean climates – including California and Mexico – and the Southeastern United States are considered to have climates suitable to the insect (Eglitis, 2000; Devorshak 2005; Seybold 2006 pers. comm). As noted above, pines native to both regions are hosts for the insect. Monterey pine is a narrowly endemic species listed by the World Conservation Union as endangered (Borchert 2006); and is under stress from the exotic pitch canker fungus (Fusarium moniliforme var. subglutinans Wollenw. & Reinking) (Seybold and Downing, 2009; Devorshak 2005).
Four pines from its native Eurasia that are often used in landscaping —Aleppo, Canary Island, Italian stone, and Scots pines (P. canariensis, P. eldarica, P. halepensis, and P. pinea) – could also be damaged. The result could be significant damage to pines in urban areas – pines are cultivated in nearly all U.S. cities (Seybold and Downing, 2009).
USFS scientists and managers developed a conservation priority-setting framework for forest tree species at risk from pest & pathogens and other threats. The Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation) uses FIA data and expert opinion to group tree species under threat by non-native pests into vulnerability classes and specify appropriate management and conservation strategies. The scientists prioritized 419 tree species native to the North American continent. The analysis identified 15 taxonomic groups requiring the most immediate conservation intervention because of the tree species’ exposure to an extrinsic threat, their sensitivity to the threat, and their ability to adapt to it. Each of these 15 most vulnerable species, and several additional species, should be the focus of both a comprehensive gene conservation program and a genetic resistance screening and development effort. Mediterranean pine engraver beetle is not known to be a threat to any of these 15 most vulnerable species.
Despite scientists’ concern, neither California nor USDA APHIS has instituted any controls on the movement of potentially infested wood or nursery stock. Scientists continue to study the insect (USFS Research & FHTET); and monitor its spread in California. APHIS considers the Mediterranean pine engraver beetle to be an “actionable” pest – which means that steps are taken when the insect is found infesting imported items or packaging (Cavey in Seybold and Downing, 2009).
International standards requiring treatment of crates, pallets, and other forms of wood packaging adopted in 2006 – if properly developed and implemented – should prevent additional introductions of the Mediterranean pine beetle via that pathway.
Borchert, D. 2006. USDA APHIS PPQ CHPST PERAL. Organism Pest Risk Analysis: Risks to the Conterminous United States Associated with the Woodwasp, Sirex noctilio Fabricius, and the Symbiotic Fungus, Amylosterium areolatum (Fries: Fries) Boidin.
Campbell, F.T. and S.E. Schlarbaum. 2002. Fading Forests II: Trading Away North America’s Natural Heritage. The Healing Stones Foundation.
Devorshak, C. and C. Hurt. USDA APHIS PPQ. 2005. NPAG et Report Orthotomicus erosus Wollaston: Mediterranean Pine Engraver Beetle Coleoptera/Scolytidae NPAG Chair Approval Date: July 14, 2005.
Eglitis, A. 2000. Orthotomicus erosus Wollaston. http://www.exoticforestpests.org/english/Detail.CFM?tblEntry__PestID=9. Web site accessed 24 January 2005.
Haack, RA. 2004. Orthotomicus erosus: a new pine-infesting bark beetle in the US. Newsletter of the Michigan Entomological Society. 49 (3-4): 3.
Lee, J.C., S.L. Smith, S.J. Seybold. 2005. USDA Forest Service State and Private Forestry Pacific Southwest Region. R5-PR-016. May 2005.
Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S., Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/
Seybold, S.J. and M. Downing. 2009. What Risk do Invasive Bark Beetles and Woodborers Pose to Forests of the Western U.S.?: A Case Study of the Mediterranean Pine Engraver, Orthotomicus erosus. in Hayes, J.L. and Lundquist, J.E. (compilers). The Western Bark Beetle Research Group: A Unique Collaboration with Forest Health Protection.” Proceedings of a Workshop at the 2007 Society of American Foresters National Convention, October 25, 2007, Portland, Oregon. USDA Forest Service Gen. Tech. Rep., GTR-PNW-784, 134 pp.