my-server
← Wiki

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 (first antennal segment) 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 (lay eggs) 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 , nematodes enter them via the thoracic spiracles.

Associations with other organisms

Bark beetles 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 (intraguild predation) 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

Gallery

Three pictures of two separate sawyers found in a planting of Scots pines in Kansas.

References

External links