Insect identification > Coleoptera > Rhynchophora > Fruit-tree bark beetle

Fruit-tree bark beetle

The shot-hole borer or fruit-tree bark beetle (Scolytus rugulosus Ratz.). This European fruit-tree pest has been in the United States also and is present nearly everywhere east of and in many localities west of the Mississippi River; it has been reported from California.

It breeds in most of the cultivated deciduous fruit trees as well as in several kinds of wild ones. The beetle is about a tenth of an inch long, almost black, except the tips of the elytra and the legs, which are dull red.

The beetles emerge from the trees in the spring but soon enter them again and dig out egg channels one or two inches long, about parallel to the grain of the wood, partly in this, partly in the inner bark. Here, in little niches or hollows along the sides, the eggs are laid. These hatch in a few days and the grubs burrow, first directly away from the egg channel, then turning in various directions, extend these larval tunnels several inches and pupate at their ends.

When the beetles have been formed there, they bore out to the surface of the tree and soon begin to tunnel in again, to lay eggs for a second generation which in the North becomes adult before winter, thus giving two generations a year.

In the South with its longer warm season, three or perhaps four generations may be produced each year, the adult beetle, in some cases at least, wintering in the tree, while in others this season may be passed in the egg stage.

Healthy trees are not often attacked except when the beetles become so abundant that a sufficient supply of weak or dying ones is not available. In healthy trees the flow of gum sometimes prevents the development of larvae but in time this becomes less and the insects then have a weakened tree to attack. Trunk, branches and twigs are perhaps equally liable to be injured. The burrows extending in all directions, partly in the outer surface of the wood, partly in the inner bark, destroy the cambium or growing layer, often entirely girdling the twig, branch or trunk, as the case may be, and causing its death.