Wood Borers

Dennis A. Haugen and Edson T. Iede

Introduction
Wood borers attack trees at different stages of tree health - recently dead trees, dying or recently cut trees, and living trees. Some species of wood borers, especially aggressive species that attack living trees, are very important pests. Wood borers are often difficult to detect in a tree, log, or wood product, within which the larval stage frequently takes up to 2 to 3 years to complete its development. Thus, wood borers are well adapted to be transported inadvertently around the world in wood products. Many of these organisms have become serious forest pests in new environments, where they lack natural controls and may encounter a susceptible tree species, even though they are insignificant pests in their native range.

Pathways
International shipments of logs are a primary pathway for transporting wood borers. Wood chips are very unlikely to harbor wood borers; the chipping process kills the developing larvae and makes the wood unsuitable for further development. Green untreated lumber can be a significant pathway, especially if the lumber has large dimensions and the wood does not rapidly dry. Untreated solid wood packing material (SWPM) has been identified as high-risk pathway as international trade has greatly increased. Low-quality wood is frequently used for making crates, pallets, and other SWPM. Wood salvaged from stands with declining or dead trees are likely to be infested with wood borers. Recently, some novel pathways for the exotic longhorned beetle have been identified, such as artificial Christmas trees with real wood boles, bonsai trees, bamboo stakes, and other wooden craft products.

Examples
Wood borers have become major forest pests in their native ranges on introduced tree species and also when introduced outside their native ranges. In this section, four woodboring species are presented as examples.

Anoplophora glabripennis (Coleoptera: Cerambycidae)

Anoplophora glabripennis

This longhorned beetle is native to China and Korea. Its native host range includes species in Acer, Morus, Populus, Prunus, Salix, and Ulmus. Unlike most temperate longhorned beetles, A. glabripennis commonly infests living, healthy trees. In China, A. glabripennis generally produces one generation per year, although some take 2 years to complete their development, and adults emerge from May to October, with peak emergence in July. It has become a pest in nonnative plantings of Populus species (e.g., P. canadensis, P. nigra, P. x euramericana) in China. As this insect has greatly increased its population in its native range, it has a higher risk of being transported and becoming established outside that range.

Infestations of A. glabripennis have been detected in the United States (New York and Illinois). The pathway for introduction has been from China through infested SWPM. The United States Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS) frequently intercepts longhorned beetle larvae in cargo from China. In the United States, eradication projects are being conducted for known infestations of A. glabripennis. Potential damage by A. glabripennis to forest ecosystems in North America has been rated as a high risk, as it is likely to alter dominant species composition in hardwood forests composed largely of maples and poplars.

Phoracantha semipunctata (Coleoptera: Cerambycidae)

Phoracantha recurva (left) and P. semipunctata (right)

This longhorned beetle is native to Australia. Its native hosts are in the genus Eucalyptus, although not all species have the same level of susceptibility. Attacked trees are usually affected by other stress factors, such as drought. Depending on climate, this beetle can produce one to three generations per year.

This Australian wood borer has been transported around the world and has established itself in many countries with Eucalyptus plantings, including New Zealand (1870), South Africa (1906), Argentina (1906), Egypt (1950), Brazil (1952), Turkey (1959), Chile (1970), Portugal (1980), and the United States (1985). It has not expanded its host range to trees outside of Eucalyptus. Its pest status appears to be related to local moisture regimes. Arid and semi-arid regions have a higher incidence of damage by P. semipunctata than moister regions. A closely related species, P. recurva, has been detected in the United States (1995), Argentina, Chile (1997), and Uruguay (1998).

Sirex noctilio (Hymenoptera: Siricidae)

Sirex noctilio, adult female (left) and larva in gallery (right)

This woodwasp is native to Europe, Asia, and northern Africa, and it reaches greatest density in the Mediterranean zone. It is generally considered a secondary pest in its native range, where it attacks stressed and dying pines (Pinus pinaster, P. sylvestris, P. nigra, P. pinea). A symbiotic fungus, Amylostereum areolatum, and a phytotoxic mucus are injected into a tree by the ovipositing S. noctilio female. The fungus and mucus kill the tree and create a suitable environment for larval development. All larval instars feed on the fungus as they tunnel through the wood. The life cycle of S. noctilio generally takes 12 months but may range from 3 months to 2 years.

Sirex noctilio is established in New Zealand (1990), Tasmania (1952), Australian mainland (1961), Uruguay (1980), Argentina (1985), Brazil (1988), and South Africa (1994). It has caused significant tree mortality in pine plantations in these countries and is considered a major pest. In New Zealand and Australia, the main host is Pinus radiata (a tree native to California), and tree mortality has reached 80% in susceptible stands. In Brazil, the main host is Pinus taeda, (a tree native to the southeastern United States), and 60% tree mortality has been recorded in unthinned stands.

Chilecomadia valdiviana (Lepidoptera: Cossidae)

Chilecomadia valdiviana

This carpenterworm is native to Chile and Argentina. Its native host range is extremely broad, including Nothofagus spp. (Fagaceae), Salix spp. (Salicaceae), Weinmannia trichosperma (Cunoniaceae), and Trevoa trinervis (Rhamnaceae). It has been found in the native hardwood forest of Chile for more than 150 years. However, little is known about its life cycle and basic behavior. It is not considered an economic pest on its native hosts.

In 1992, C. valdiviana was found to be attacking Eucalyptus nitens (Myrtaceae) plantations in Chile. It infests live trees greater than 4 cm in diameter, with attacks occurring in all parts of the bole. Tree stress is not a prerequisite for attack. This wood borer does not kill the tree directly. However, larval galleries weaken the bole, and the infested tree is more susceptible to wind breakage. Also, the open larval gallery provides easy entry for stain and decay fungi, which rapidly colonize the wood and reduces its value. In Chile, C. valdiviana occasionally infests Eucalyptus camaldulensis and E. gunnii. The pest status of C. valdiviana could greatly increase if it became established in new areas.