Monochamus
Monochamus is a genus of longhorn beetles found throughout the world. They are commonly known as sawyer beetles or sawyers, as their larvae bore into dead or dying trees, especially conifers such as pines. They are the type genus of the Monochamini, a tribe in the huge long-horned beetle subfamily Lamiinae, but typically included in the Lamiini today.
If sawyer beetles infect freshly cut pine logs, they can cause a 30–40% loss in value due to the tunnels their larvae bore. It is important to process logs within a few weeks of cutting or store them in water to minimize damage. Some species are known to transport phoretic Bursaphelenchus nematodes, including B. xylophilus which causes pine wilt disease.
Description
Beetles in this genus are black or mottled gray in colour. Like other Lamiinae, the head is oriented vertically with ventral mouthparts. The scape has a circatrix, a carinate ring or scar-like area near the tip. Antennae of females are roughly as long as the body, while antennae of males are twice as long. The tarsal claws are divergent.
Life cycle
Adults feed within the crowns of healthy trees. Adult females oviposit in slits in the bark of dying or dead trees. Larvae hatch from eggs and develop in wood, passing through several instars. Next is a pupal stage. In spring, new adults emerge, starting the life cycle again.
Association with nematodes
The pine wood nematode Bursaphalenchus xylophilous is transmitted by several Monochamus species, and its life cycle is tied with that of its vector.
When nematode-infested adult Monochamus feed on healthy trees, they create wounds that allow nematodes to enter. In a susceptible host tree, nematodes breed in the xylem and eventually kill the tree. In a resistant host, the nematodes die instead.
When nematode-infested adult Monochamus oviposit in dying or dead trees, the slits they make in the bark for their eggs also allow nematodes to enter. Nematodes reproduce and feed on wood cells or fungi. Eventually, new Monochamus adults emerge from pupae, and while these are still callow, nematodes enter them via the thoracic spiracles.
Associations with other organisms
s oviposit on trees at around the same time as Monochamus, and they transmit blue stain fungi. Bursaphalenchus nematodes feed on this fungi, and the combination of fungi and nematodes may help in overcoming host tree defences, creating a more suitable habitat for bark beetles and Monochamus. Additionally, Monochamus compete with bark beetles for resources, prey on them and use their semiochemicals as kairomones.
Some species of braconid wasps in the genus Atanycolus are parasitoids of Monochamus, along with other wood-boring beetles.
The black-backed woodpecker is a predator on larvae of wood-boring beetles, including Monochamus.
Taxonomy
The genus is very large, and its boundaries have varied considerably over time, with many species placed in this genus that have long since been removed, and species placed in other genera that have been added, and there are at least 20 subgenera presently recognized by most authorities.
Species
Monochamus abruptus Holzschuh, 2015Monochamus accri Monochamus adamitus Thomson, 1857Monochamus affinis Breuning, 1938Monochamus alboapicalis Monochamus alboscutellaris Breuning, 1977Monochamus alternatus Hope, 1842 – Japanese pine sawyer beetleMonochamus aparus Monochamus asiaticus Monochamus asper Breuning, 1935Monochamus atrocoeruleogriseus Gilmour, 1956Monochamus balteatus Aurivillius, 1903Monochamus basifossulatus Breuning, 1938Monochamus basigranulatus Breuning, 1952Monochamus basilewskyi Breuning, 1952Monochamus benito Monochamus bialbomaculatus Breuning, 1948Monochamus bimaculatus Gahan, 1888Monochamus binigricollis Breuning, 1965Monochamus binigromaculatus Breuning, 1959Monochamus blairi Monochamus bootangensis Breuning, 1947Monochamus borchmanni Breuning, 1959Monochamus buquetii Monochamus burgeoni Breuning, 1935Monochamus camerunensis Aurivillius, 1903Monochamus carolinensis – Carolina sawyerMonochamus clamator – spotted pine sawyerMonochamus conradti Breuning, 1961Monochamus convexicollis Gressitt, 1942Monochamus dayremi Breuning, 1935Monochamus densepunctatus Breuning, 1980Monochamus dentator Monochamus desperatus Thomson, 1857Monochamus diores Monochamus dubius Monochamus fisheri Breuning, 1944Monochamus flavosignatus Breuning, 1947Monochamus flavovittatus Breuning, 1935Monochamus foraminosus Holzschuh, 2015Monochamus foveatus Breuning, 1961Monochamus foveolatus Hintz, 1911 Monochamus franzae Monochamus galloprovincialis – black pine sawyer or timberman beetleMonochamus gardneri Breuning, 1938Monochamus grandis Waterhouse, 1881Monochamus granulipennis Breuning, 1949Monochamus gravidus Monochamus griseoplagiatus Thomson, 1858 Monochamus guerryi Pic, 1903Monochamus guttulatus Gressitt, 1951Monochamus impluviatus Motschulsky, 1859Monochamus inexpectatus Breuning, 1935Monochamus irrorator Monochamus itzingeri Breuning, 1935Monochamus jordani Nonfried, 1894Monochamus karlitzingeri Tavakilian & Jiroux, 2015Monochamus kashitu Monochamus kaszabi Heyrovský, 1955Monochamus kinabaluensis Hüdepohl, 1996Monochamus kivuensis Breuning, 1938Monochamus laevis Jordan, 1903Monochamus lamottei Lepesme & Breuning, 1952Monochamus latefasciatus Breuning, 1944Monochamus lepesmei Breuning, 1956Monochamus lineolatus Monochamus lunifer Monochamus luteodispersus Pic, 1927Monochamus maculosus Haldeman, 1847 – spotted pine sawyerMonochamus marmorator Kirby in Richardson, 1837 – balsam fir sawyerMonochamus maruokai Hayashi, 1962Monochamus masaoi Kusama & Takakuwa, 1984Monochamus mausoni Breuning, 1950Monochamus mbai Lepesme & Breuning, 1953Monochamus mediomaculatus Breuning, 1935Monochamus melaleucus Jordan, 1903Monochamus mexicanus Monochamus millegranus Bates, 1891Monochamus murinus Monochamus nigrobasimaculatus Breuning, 1981Monochamus nigromaculatus Gressitt, 1942Monochamus nigromaculicollis Breuning, 1974Monochamus nigroplagiatus Breuning, 1935Monochamus nigrovittatus Breuning, 1938Monochamus nitens Bates, 1884Monochamus notatus – northeastern sawyer or notable sawyerMonochamus obtusus Casey, 1891 – obtuse sawyerMonochamus ochreomarmoratus Breuning, 1960Monochamus ochreopunctatus Breuning, 1980Monochamus ochreosparsus Breuning, 1959Monochamus ochreosticticus Breuning, 1938Monochamus olivaceus Breuning, 1935Monochamus omias Jordan, 1903 Monochamus pentagonus Báguena, 1952Monochamus pheretes Monochamus philomenus Monochamus pictor Monochamus principis Breuning, 1956Monochamus pseudotuberosus Breuning, 1936Monochamus quadriplagiatus Breuning, 1935Monochamus rectus Holzschuh, 2015Monochamus regularis Monochamus reticulatus Monochamus rhodesianus Gilmour, 1956Monochamus roveroi Teocchi, Sudre & Jiroux, 2015Monochamus rubiginosus Teocchi, Sudre & Jiroux, 2014Monochamus ruspator Monochamus saltuarius Gebler, 1830 – Sakhalin pine beetle Monochamus sargi Monochamus sartor – black fir sawyerMonochamus scabiosus Monochamus scutellatus – white-spotted sawyer or spruce sawyerMonochamus semicirculus Báguena, 1952Monochamus semigranulatus Monochamus serratus Monochamus shembaganurensis Breuning, 1979Monochamus similis Breuning, 1938Monochamus sparsutus Fairmaire, 1889Monochamus spectabilis Monochamus strandi Breuning, 1939Monochamus stuhlmanni Kolbe, 1894Monochamus subconvexicollis Breuning, 1967Monochamus subcribrosus Breuning, 1950Monochamus subfasciatus Monochamus subgranulipennis Breuning, 1974Monochamus subtriangularis Breuning, 1971Monochamus sutor – pine sawyerMonochamus taiheizanensis Mitono, 1943Monochamus talianus Pic, 1912Monochamus thoas Monochamus thomsoni Monochamus titillator – southern pine sawyerMonochamus tonkinensis Breuning, 1935Monochamus transvaaliensis Gilmour, 1956Monochamus triangularis Breuning, 1935Monochamus tridentatus Chevrolat, 1833Monochamus tropicalis Monochamus vagus Monochamus variegatus Monochamus verticalis Monochamus villiersi Breuning, 1960Monochamus x-fulvum Bates, 1884