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nesting-boxes (Figs. 132-135) should be hung or nailed up in the woods, to protect their eggs and young against cuckoos, cats, and other enemies. In place of more elaborate boxes, small nesting-cases can easily be made from pole-thinnings of Pine or Spruce cut into 8- or 9-inch lengths, hollowed out, drilled and pegged at
the outer side, and capped and closed above with a bit of wood, when they are ready for nailing on the trees.
Exterminative Measures can only be effective when based on knowledge of the appearance, habits, and life-history of injurious insects, and on constant attention being paid to all recent plantations or felling areas, windfalls, and sickly
and backward crops, which may easily develop into breeding-places. Frequent inspection of conifer woods and plantations is particularly advisable.
Noxious insects may be discovered by numerous indications. Bore-holes in trees, bore-dust on cobwebs and on the ground below, or drops of resin on the bark or at the foot of poles or trees, all show that insects are at work in the trees and poles ; and gnawed leaves or excrement seen on paths and in cart-ruts, and a gradual thinning of the tree-crowns, show that moth-caterpillars are feeding there. But even before the tree-crowns become noticeably thinner, a palpable increase in the number of insectivorous birds may suggest that moth-caterpillars are present in unusual numbers.
When it is either known or suspected that injurious insects are present and likely to damage the woods, the exterminative methods to be adopted vary according to the habits of the insects in question. To determine the easiest point of attack against it, a knowledge of its life-history is necessary ; but as the usual methods adopted against beetles are entirely different from those used against moths, these two orders of insects form two distinct groups as regards methods of extermination.
A. Extermination of Beetles.- Many of the bark-beetles and weevils breeding chiefly in conifers can be kept in check by felling and barking the timber and burning the bark containing the eggs, larvæ, pupæ, and often the beetles themselves. The foresters and woodmen should be trained to look out for and detect infested stems, and be taught the advantage of felling a tree here and there as decoystems to trap egg-laying beetles and prevent the ovideposition in healthy stems."
Decoy-stems should be felled and placed before the insects pair, because many of them first of all search for sickly and recently felled trees before attacking healthy stems, the strong resinous outflow from which might kill their brood. Stems laid down as decoys in winter or early spring should be barked and removed in May and June, and fresh decoy-stems placed in summer to catch any second brood in August. Poles or trees that are dominated or suppressed, but still healthy, should be used in preference to half-dry stems already moribund, because the latter are not so likely to attract the ovidepositing females. It is best to raise the decoy-stems off the ground on rests, so as to let the beetles breed on the lower side, which remains sappy when the upper half is already becoming dry. The branches should be lopped from the stems to check evaporation through the foliage ; but they can also be set as traps for many species of beetles. Timber from any winter fall is always more or less infested with beetles, and should be removed and barked not later than the middle of May. Removal alone is not enough, because in the sawyard or elsewhere the broods hatch out and the number of beetles increases greatly.
Decoy-stems should be examined occasionally to see if they are acting well as traps for eggs. Small drops of resin or heaps of bore-dust near the punctures and bore-holes will give the information required; but pieces of bark should also be cut off and inspected to see how far the young brood has developed. When the largest larvæ are about half-grown is the best time for stripping and burning the bark, because ovideposition is then completed, and there is no danger of the beetles laying more eggs elsewhere.
Larvæ can only be collected in the case of cockchafer grubs in nurseries, and the collection of the mature beetles is most practicable with large kinds like cockchafers and longicorns, which can be shaken or tapped down from the crowns of poles or young trees. The large Pine-weevil can be trapped in narrow ditches with vertical walls, and killed by treading on them or pouring boiling water over them. Smaller beetles than these may be trapped in bundles of brushwood or bark, which should then be burned.
See reference made to exterminating bark-beetles, in footnote to p. 74.
Continental Methods.- In the great forests of Central Europe destruction by insects sometimes assumes proportions impossible in Britain, and even very much more destructive than our Larch disease. The best preventive measures have been found to consist in careful thinning of the woods. Whenever dominated or suppressed stems fall into a sickly state, they become predisposed to attacks of injurious insects and fungous diseases; hence they soon develop into breeding - centres. The preventive measures that can be taken by the forester are :
1. Only to grow crops of trees suitable for the given soil and situation. 2. Formation of mixed woods in preference to pure forests. 3. Careful thinning and tending of the woods, and immediate removal of sickly
stems. 4. Frequent examination of the woods and of the condition of the timber crops. 5. Grubbing up stumps of conifers, if possible, before replanting the area. 6. Making falls of coniferous timber only in spring, summer, and autumn, and bark
ing the logs (Fig. 136). Where winter felling is necessary, a few trees should be ringed and left standing here and there as decoy-stems to attract barkbeetles. These should then be felled and barked, and the bark burned to pre
vent the ova and larvæ developing into mature insects and multiplying. 7. Speedy removal of all thinnings and falls of timber, and clearance of the branches
and brushwood. B. Extermination of Moths.—When attacks of caterpillars occur on any large scale, no such remedies as decoy-trees can be applied ; nor can spraying with lime-water, solutions of sulphur, tobacco-juice, quassia, paraffin, carbolic acid, Paris green, London purple, &c., take place in extensive woodlands, although suitable and practical in nurseries and orchards. Although something can always be done to destroy the ova, pupæ, and imagines of moths, yet it is mainly during the caterpillar stage that efforts to exterminate them are successful.
Sometimes hairy caterpillars may be hand-picked by workmen wearing old gloves to protect their hands. Hand-picking can also be adopted for caterpillars which hibernate on the ground under moss, &c., or which can be brought down by shaking the poles or tapping on tree-branches with padded mallets or flat axeheads, or which are found in trenches dug for this purpose. By shaking and tapping the Pine Span-worm caterpillars may be brought down to the ground and collected ; and this method is most effective early in the morning and during cool weather, when the caterpillars have a much looser foothold on the foliage than during warm sunshine. The clusters of caterpillars of the Lackey-moth can also easily be crushed or burned.
When severe attacks are confined to small areas, the migration of caterpillars to adjoining woods may be prevented by digging narrow trenches (about 1 foot deep, and with perpendicular walls) round the infested portions, and ensuring that the leaf-canopy overhead is also interrupted. In these trenches holes, also with clean-cut upright sides, should be made here and there along the sole to catch the caterpillars and lessen their chance of escape. To assist the work of extermination it is also well to cut similar ditches within the area isolated.
One of the lessons taught by the ravages of the Spruce-moth (Liparis monacha, rare in Britain, see p. 107) in Bavaria and Western Austria about twelve to fourteen years ago (which cost £100,000 in exterminative measures alone, and involved the clearance of many millions of trees killed by the moths, and by beetles following after them) is the efficacy of grease-banding, by forming rings or girdles of patent glue or viscous tar around all stems in infested areas. These bands hinder caterpillars from ascending the trees to feed on the foliage ; or, if the caterpillars are once up, the bands prevent them descending to moult or pupate. Caterpillars which hibernate under moss, &c., on the ground are thus
Spruce-bark is there saleable with profit as tanning material.
Clear-felling of a Spruce-wood, mixed with Scots Pine and Beech (Tharandt, Saxony, 1900). The conifers are at once barked for protection against beetles, the bark being collected and
stacked, and the brushwood piled in heaps ready for sale. Narrow rings of bark are left at the ends and in the middle of each log, to minimise the number and size of the cracks formed by shrinkage during the natural process of seasoning.
A sample-plot ringed with bands of patent tar to ascertain if the Nun-moth (Liparis
monacha) is present in the woods (near Dresden, Saxony, 1900).