A bark beetle is one of about 6,000 species in 247 genera of beetles in the subfamilyScolytinae. Previously, this was considered a distinct family, but is now understood to be specialized clade of the "true weevil" family. Although the term "bark beetle" refers to the fact that many species feed in the inner bark layer of trees, the subfamily also has many species with other lifestyles, including some that bore into wood, feed in fruit and seeds, or tunnel into herbaceous plants. Well-known species are members of the type genusScolytus, namely the European elm bark beetleS. multistriatus and the large elm bark beetle S. scolytus, which like the American elm bark beetle Hylurgopinus rufipes, transmit Dutch elm diseasefungi. The mountain pine beetleDendroctonus ponderosae, southern pine beetleDendroctonus frontalis, and their near relatives are major pests of conifer forests in North America. A similarly aggressive species in Europe is the spruce ips Ips typographus. A tiny bark beetle, the coffee berry borer, Hypothenemus hampei is a major pest on coffee plantations around the world.
Ecology
Bark beetles reproduce in the inner bark of trees. Many species, such as the mountain pine beetle attack and kill live trees. Most, however, live in dead, weakened, or dying hosts. Bark beetles of the subfamily Scolytinae feed and breed between the bark and the wood of various tree species, including spruces. More than 20 species feed on weakened, dying, or dead spruce, fir, and hemlock. Most restrict breeding area to one part of the tree: twig, branch, stem, or root collar. Some breed in trees of only one species, others in trees of many species. Bark beetles often attack trees that are already weakened by disease, drought, smog, overcrowding, conspecific beetles, or physical damage. Healthy trees may put up defenses by producing sap, resin or latex, which may contain a number of insecticidal and fungicidal compounds that can kill or injure attacking insects, or simply immobilize and suffocate them with the sticky fluid. Sap is one of the first line of defense of pines against bark beetles. Released sap or resins can plug bored holes of bark beetles and seals wounds. Resins also trap insect pests making some initial entry by bark beetles unsuccessful. Under outbreak conditions, the sheer number of beetles can overwhelm the tree's defenses with resulting impacts on the lumber industry, water quality, fish and wildlife, and property values. According to the United States Department of Agriculture, native bark beetles can cause high levels of tree mortality in California. Massive outbreaks of mountain pine beetles in western North America after about 2005 have killed millions of acres of forest from New Mexico to British Columbia. Most studies of wildfire after beetle outbreaks have found no effect of beetle-caused tree mortality on wildfire size or severity. damaged by Ips typographus and clearings after consecutive logging Management of bark beetle infestation in the Šumava National Park in the Czech Republic's Bohemian Forest has been controversial with some advocating non-intervention and others supporting harvesting of infested old-growth trees.
