Insect identification > Coleoptera > Rhynchophora > Bark beetles

Bark beetles


Family Ipidae (formerly Scolytidae) (bark beetles or engraver beetles). The members of this family are borers and nearly all attack the bark or wood of trees.
They are small insects, from one twenty-fifth to two­fifths of an inch long, brownish or blackish in color, and usually with cylindrical bodies. In habits they form two chief groups. In the socalled Ambrosia beetles the tunnels extend through the wood and the young develop there; in the true bark beetles the tunnels are formed either in the inner bark or between this and the wood.

The adult in either case cuts a tunnel slightly larger than itself in to the inner bark or through this, but the ambrosia beetles continue it on into the wood. The bark beetles, having arrived at the desired depth, turn and excavate one or more channels between the bark and the wood, which become the egg tunnels. Along the sides of these the eggs are deposited, singly in little hollows, several together in larger excavations, or many in grooves of the tunnel.

The larvae, on hatching, excavate tunnels for themselves, leading away from the egg tunnel and becoming larger with the growth of the larvae. Pupation is at the end of the larval tunnel in a somewhat wider portion and after transformation the adult bores its way to the outside. In the case of the Ambrosia beetles a fungus used as food by the insects grows on the walls of the tunnels and generally turns these walls black.

Destruction by these insects is mainly of forest and shade trees. As nearly all the bark beetles appear to prefer dying bark in which to live, the refuse of cutting operations, commonly termed "slash," will provide much of this, and most of the insects will work there. When slash comes to an end, however, by operations ceasing in that area, the increased abundance of the insects due to abundant slash often forces them, for lack of other material, to turn to the healthy trees, themselves changing thereby from "secondary" to "primary" foes.

Slash should therefore be destroyed before beetles in it can develop to the adult condition. Fire in forests produces many dead and weakened trees also, frequently leading to insect attacks, and epidemics, either local or quite widespread, may thus result.

Many trees, when the beetles bore into them, pour out their sap or resin, and some of the insects may easily be drowned in this. If attacked by multitudes, however, the supply of sap becomes so reduced that the insects coming later can accomplish their purpose.

Removing "beetle trees" before the adults escape and removing and burning the bark; floating the logs; or sawing the same winter and burning the slabs and trimmings are some of the measures used for the protection of our forests against these insects.

One species of ipid, the clover root borer, tunnels in the main roots of clover. Several other species attack fruit trees, usually those not healthy.