Fig. 146.

Fig. 147.

(a) The Common Ash-bark Beetle (Hylesinus fraxini) is the commonest and most destructive species all over Britain. When once it bores into healthy Ash-poles and trees (as is often the case) they soon sicken, then become much infested, and are quickly killed (Fig. 145).

Life-history. The beetles emerge from their winter quarters in late April or early May, and bore into the stem and branches of standing Ash-trees or in felled stems in order to lay their eggs. Ash-logs lying in woods or parks till May or June are usually the breeding-places for thousands of these beetles. Felled timber forms perhaps their chief breeding-places.

In a few days the larvæ hatch out (in May), from twenty to sixty eggs being laid along each arm of the (2-armed) mother-gallery, which varies from 2 to 4 inches in length. They are reddish or purplish at first, with brown head and jaws, and are legless, transversely furrowed, and tapering to a point at the tail. The larvalgalleries, formed at right angles to the main-gallery, vary from an inch up to 4 inches in length (usually 2 to 4 inches), according to the more or less crowded and infested condition of the bark. The larvæ feed for about ten weeks, then pupate either in the bark (when it is thick) or in the sapwood (when the bark is thin). The young beetles emerge in August (when their exit-holes give the trees the appearance of having been riddled with shot), and at once proceed to hibernate in the bark of neighbouring live Ash-trees or freshly-felled logs, where they bore right into the cambium. Here they form galleries and feed during the autumn, then remain dormant in winter, and feed again in March and April, before emerging for pairing.

Prevention and Extermination consist mainly in planting Ash only on soil and situations really suited to it; in removing felled timber before August; in cutting out sickly Ash-poles and trees at least by February and March; and in barking infested stems in June and July, and burning the bark. In parks, Ashlogs may be left as decoys, the bark being peeled and burned as above.

(b) The Black Ash-bark Beetle (Hylesinus crenatus) is generally to be found at work along with H. fraxini. It usually only attacks weakly old trees, or those already injured by H. fraxini; but when once it infests such, it breeds there till the tree is killed (Fig. 146).

Life-history. The beetles appear and pair from May to August, but chiefly in July and August. They lay their eggs in the cambium of old, weakly, overmature, or sickly trees with thick bark; but failing such, healthy trees and dead stems are attacked. Eggs are rarely deposited in felled timber. The beetles form 2-armed mother-galleries cutting into the sapwood, and sometimes extending up to 4 or 5 inches in total length, and about of an inch wide. The white elongated eggs are laid in niches on the upper and lower sides of the gallery, and numbering from 10 to 30 in each arm.

The larvæ are long, legless, tapering, pearl-white, wrinkled maggots, with brown head and jaws. On hatching out they eat deeply into the sapwood in fairly straight and parallel lines, but soon diverge and become tortuous, crowded, and confused. Later on they eat more in the bark, and most of them form their pupal-chambers there rather than in the sapwood. They are more or less active throughout the winter in mild seasons, and only pupate in the following spring, to emerge as beetles some time between May and August. Thus the normal generation takes about 12 months, while stragglers need 15 to 18 months. The beetles emerging in August and September sometimes bore and ovideposit in the same autumn, but more often they hibernate like H. fraxini, and do not pair and lay their eggs till the following spring. In the latter case mother-galleries are at

once formed, but without the niches for placing the eggs. Thus both larvæ and hibernating beetles can often be found in infested stems.

Prevention and Extermination consist in at once felling and removing Ashtrees found to be infested.

(c) The Ash-branch Beetle (Hylesinus oleiperda) also often attacks along with H. fraxini in England, but is not found far north in Scotland. It is a pest in the Olive-groves of Southern Europe (whence its name), but in England it only attacks the twigs of Ash-trees. Sometimes it breeds in dead and decaying branches, but generally in sickly shoots and fresh sappy windfall branches (Fig. 147).

Life-history. The beetles mostly fly in July and August (stragglers later), pair, and lay eggs on small branches up to about 1 inch diameter in healthy and growing trees (being sometimes also found on coppice-shoots), or up to about a foot diameter in sickly and moribund trees. It does not attack any part of largesized trees covered with thick bark. The broad 2-armed galleries are bored by the beetles deep in the sapwood, and are widened into short spurs near the long entrance-gallery. The arms of the mother-gallery are seldom more than an inch long, and in each arm from 10 to 20 eggs are laid rather closely together. Eggs of late stragglers may be found as late as October in the mother-galleries.

The larvæ, marked with pink lines near their lower end, eat deep in the sapwood. Their galleries are usually 6 to 8 or 10 inches long, and are at first fairly parallel, but afterwards often cross each other and become confused and irregular. This irregularity, and the long entrance-gallery, form easy marks of distinction between the borings of this beetle and of the much more regular H. fraxini. The larvæ are more or less active throughout mild winters, then pupate in spring in the sapwood, to emerge as beetles in the following July and August. Its generation is therefore simple annual, the life-cycle extending over 12 months.

Prevention and Extermination are much the same as for H. fraxini, except that small branches form the best beetle-traps, because thick-barked stems are not suitable breeding-places. The decoy-branches should be collected from August to October, and removed for use as fuel, &c.

2. The large Pine-Beetle (Hylesinus (Hylurgus) piniperda).—Next to the Pine-weevil this is the most destructive insect in our Pine-woods. It attacks plantations at nearly all stages of growth, till the trees are well advanced in age. Besides attacking young growing branches, it is also found in decaying branches left in the woods. Much of the damage attributed to this beetle in Scotland is, however, no doubt due to Hylesinus palliatus, which often attacks Pine-woods along with H. piniperda (Fig. 148).

This insect does far less damage as a grub than as the fully matured beetle. Owing to the strong flow of resin from healthy stems, it chiefly attacks felled timber or sickly and unhealthy plantations; and healthy trees are only attacked when the pest has increased to excessive numbers. The attacks of the beetle are usually worst along the edge of green lanes and in pole-woods, where it may easily become an annual nuisance, interfering with the normal growth of the crown, and often doing serious damage. Woods in the vicinity of timber depots, saw-mills, &c., are specially liable to its attacks.

Appearance. The Pine-beetle (Figs. 148-150) is to of an inch in length, and almost cylindrical. On first emerging it is reddish-brown, then turns mostly glossy black or dark-brown, with a black thorax, and reddish-brown (knobbed) feelers and legs. The wing-ca ses have longitudinal rows of very fine punctures, the spaces between which are wrinkled with punctures and small knobs, and have a row of little knobs with brush-like tufts of thick hair. But as the second space on each side of the middle line on each wing-case has no tubercle near the end, it therefore appears somewhat indented or slightly pressed in (which distinguishes it from H. minor, an almost purely Continental species).

Life-history. The Pine-beetles emerge from their pupal-chamber or their winter quarters late in March (in dry warın years) or in April, then pair and lay eggs under the bark of newly-felled stems or in stacked fuel. If such breedingFig. 149.

places are wanting, it attacks sickly trees, depositing the ova in thick-barked portions of the tree, or in recently cut Pine stumps. So long as such breeding places are obtainable it selects for ovideposition the Scots or some other species of Pine (Weymouth Pine is often attacked), although it also occasionally makes use of Spruce and Larch.

After pairing, the female generally enters some bark-fissure, bores under it, and lays its eggs along a vertical main-gallery commencing with a curve and then stretching about 3 to 5 inches parallel to the axis of the stem. The boring of the mother-gallery and the ovideposition continue for 3 to 5 weeks, up to 100-120 eggs being laid close to each other in niches cut right and left along the edges of the main-gallery. The bore-holes, where an entrance is effected, are sometimes marked by the yellowish outflow of resin on the bark.

On hatching out after an egg-stage of 14-20 days the larvæ do not bore into

the sapwood, but eat sinuous galleries in the cambium on each side of the maingallery, and after about 8 weeks they pass through the chrysalid stage (about 14 days) in pupal-chambers formed in the bark. The beetle, at first brighter in colour than afterwards, usually issues in June, about 11 to 12 weeks after ovideposition (or later if the spring has been cold and backward). As many beetles may breed in one stem after their issue, it may sometimes look as if riddled with snipe-shot. The beetle bores its way out through the bark, and may either at once pair and produce a second generation within the year, or else it may bore into young Pine-shoots for food and shelter (Fig. 150), and may then breed either during any of the warmer months, or not until the following spring. Warm weather favours a double generation.1

The beetles belonging to the second generation, as well as stragglers of the first generation, late in developing, bore into the tops of the youngest Pine-shoots just below the buds (the entrance-hole being generally noticeable by a shell of resin round it), feed on the pith, and either turn and leave again by the entrance-hole, or else make a special exit-hole. Shoots thus hollowed break during storms and fall to the ground, while the trees attacked look somewhat as if they had been pruned. When the attacks have been frequently repeated, the crowns assume a pointed pyramidal shape, from continuous loss of side-shoots, and the trees often become stag-headed. The beetle hibernates either in bark-fissures or under moss, or even more commonly by boring into the thick bark of the collar of the stem near the ground.

Prevention and Extermination.-Like the other bark-boring beetles, its chief natural enemies among insects are Clerus formicarius and Rhizophagus depressus. The best measures consist in keeping the woods clean, removing all windfalls and sickly trees, or stems having bore-dust lying round them, or on which the white shells of resin and the entrance-holes in the thick bark indicate that they are already infested. Decoy-stems may also be placed here and there during spring and summer, from which the bark should be peeled and burned at the proper time. Winter-felled timber may thus be used; but if not removed from the woods by the end of May, it certainly ought then to be barked.

Collecting and burning the hollowed shoots and twigs lying scattered on the ground is of little use, as the beetles have usually emerged from them before they break off.

Most trees are felled in autumn and winter, and to leave Pines lying in their bark in or near woods till the middle of the following summer is a sure way to propagate this and many other destructive forest insects. There need be no fear of the Pine-beetle breeding in stems from which the bark has been removed, but the barking of winter-felled Pines is a somewhat expensive proceeding. The removal of the trees, or their conversion before the month of June, should always be attended to, but the ideal method of procedure is as follows. Let the trees felled in autumn or winter remain in or near the wood till the month of May, by which time they will have attracted most of the Pine-beetles in the

1 Tracing out the life-cycle in one brood, the following might stand as a calendar in favourable weather conditions (Prof. R. S. MacDougall, in Trans. High. and Agri. Socy. Scot., vol. xiv., 1902, p. 232) :—