BARK BEETLE

also called Engraver Beetle, any member of the insect family Scolytidae (Ipidae, with more than 2,000 species) of the order Coleoptera. They are cylindrical, usually under 6 mm (0.25 inch) long, brown or black in colour, and often very destructive. The male and femalesometimes as many as 60 females are found with each malebore into a tree and form an egg chamber. The female deposits her eggs in niches along the sides of the chamber. After the eggs hatch, the larvae bore away from the chamber, forming a characteristic series of tunnels. Each larva pupates at the end of its tunnel and emerges as an adult through a hole bored in the bark. Different species of bark beetles attack particular trees, damaging roots, stems, seeds, or fruits. Diseases are transmitted by some beetles. For example, the elm bark beetles of the genera Scolytus and Hylurgopinus carry the spores of the fungal Dutch elm disease. When bark is removed from affected trees, the arrangement of the galleries can be seen on the wood surface. Each species of elm bark beetle produces a distinctive gallery pattern. Most species of Ips and Dendroctonus attack pines, and the larvae of the clover root borer Hylastinus obscurus damage clover roots. Other insects sometimes included in this family are the ambrosia beetles, also called timber beetles, which bore into the wood of trees, thereby destroying much timber. The female constructs a long central gallery, off of which are the egg chambers. On a pile of excrement and wood chips in the main chamber, she cultivates a fungus for food. The galleries of the ambrosia beetle are recognized by their uniform size and dark stain, which is caused by the fungus growing on the wall.