Pine Bark Beetles
Numerous species of small beetles (never exceeding 1/4in. in length, and usually not over 1/6in. or 1/8in.) live below the bark of Fir-trees and other Conifers. They have a great general similarity in appearance, the body being usually nearly cylindrical, or slightly flattened from above downwards; the wing-cases are rounded down at the hinder end and along the sides. The colour is a shade of brown, sometimes approaching pitchy-black; but it is often modified by a coating of short hairs of a different hue. The females burrow through the bark, and form a tunnel between it and the wood, a task facilitated by their form. The burrows vary greatly in details, each species of beetle forming its own characteristic and easily-recognised type of burrow. Along the sides of this the eggs are placed at intervals; and the larvae, as soon as hatched, make burrows for themselves, usually diverging from that of the mother in such a way as to avoid interfering with each other. They have no legs, are fleshy, and are nearly white in colour. They become pupae generally in their tunnels, and the beetles emerge from them about June and July, or there may be two broods. For egg-laying, they almost always select trees in an unhealthy state: hence, their ravages as larvae do little real harm to forests; but, in the case of ornamental Conifers, they may, at times, destroy choice plants that, but for this additional foe, might have recovered. A number of the species found in this country, e.g., Hylesinus ater, H. opacus, Tomicus bidentatus, and T. Laricis, as beetles, have been observed to injure the Firs and other Conifers by gnawing the bark of young shoots; and they are known to kill young plants, even up to the tenth year of growth, by stripping the bark from the base of the stem. Others, and among these notably Hylesinus piniperda, bore into young twigs, and eat out the pith in the centre, from the base towards the tip. The twigs die, dry up, and fall off, frequently in considerable numbers. If the leading shoots have been pierced, the form and value of the tree are largely affected. The genera and species of Bark Beetles are so much alike that the distinctive characters are recognisable only by practised entomologists: hence, it is vain to attempt to give descriptions of the many species that are to be met with on Firs and other Coniferae in Britain. Remedies. The Beetles prefer to lay their eggs under the bark of tree-stumps, cut branches, brushwood, &c.: hence, it is advisable to remove and burn all such refuse, without delay, except so much as may be left as a trap to attract the females; and this also should be burned after the purpose is served. The traps should be renewed every three or four weeks, while the Beetles are out, i.e., from early spring till the end of July, and again in late autumn, since some species appear in autumn, and hybernate. All diseased plants, if small, should be uprooted and burned. Badly-diseased trees, if too large to be entirely burned, should have the bark stripped off and burned. It is hardly possible to do anything to preserve a tree that has been severely attacked, more especially as it is almost always suffering from other causes; and the better course is to uproot and destroy all such trees at once. If the attack is slight, and the tree is a valuable one, it may be possible to stop the evil by measures to promote the growth of the tree, thereby rendering it unsuited to the taste of the insects. An insecticide, such as Gishurst's Compound or petroleum, may also be injected into such holes as can be discovered in the bark, in order to destroy the beetles or larvae in them.