Sidebilder
PDF
ePub

Prevention and Extermination.—If timber infested be barked or removed from the woods before the beetles emerge in July, this should suffice to prevent any large increase of the insect. Decoy-stems can also be laid down as traps, as for other bark-beetles.

5. The Acuminate Bark-Beetle (Bostrichus (Tomicus) acuminatus). This is sometimes rather a destructive beetle in Scots Pine woods in Scotland and the north of England, where it infests the crowns of middle-aged and maturing crops.

Appearance.—The beetle is about što of an inch long, and brown with yellowish-grey down. The wing-cases have regular rows of punctures, and are sharp-pointed where they come together near their upper end (hence the scientific name); and each wing-case has there 3 tooth-like processes, the third being the largest.

Life-history.The beetles fly in April and May, when the female lays her eggs high up in the crown of old Scots Pine. The brood-galleries are stellate, with 3 to 5 arms radiating from a rather large pairing-chamber, and biting deep into the sapwood. The larval-galleries are mostly in the cambium, and are confused and irregular, often crossing each other. Like most of the other Bostrichini, the beetles emerge in July and August, and pair and produce another brood, which emerges as beetles in autumn, that hibernate under the bark (along with late stragglers of the summer brood), and pair in the following spring.

Prevention and Extermination consist in felling and removing mature timber before the spring is far advanced, and in thinning out sickly trees in woods approaching maturity. As the eggs are laid high up in the crowns of old trees, it is difficult to operate against this beetle by means of decoy-trees as traps.

6. The Wood - boring or Three-striped Bark-Beetle (Bostrichus (Xyloterus) lineatus). In the north-east of Scotland this beetle attacks most conifers, but chiefly Scots Pine, Spruce, and Larch, and it has not as yet proved very destructive. It mainly attacks recently-felled timber, and is only exceptionally to be found in standing crops of poor growth. It differs from all the previously described bark-beetles in its habits and life-history, and injures timber by boring into the wood, often riddling it with holes. But as the galleries, fortunately, are for the most part confined to the sapwood, the damage is not so great as it otherwise would be.

Appearance. This small timber-boring Bostrichus is cylindrical and blackish, about $ to } of an inch long, with dull yellow-brown wing-cases, antennæ, and legs, and with three dark longitudinal stripes along the inner and outer edges and the middle of each wing-case (whence lineatus). It has no tooth-like processes at the ends of the elytra like the bark-beetles previously described.

Life-history.— The beetle flies in March and April, and lays its eggs in timber lying in the woods. The female bores straight into the stem for about 1 to 2 inches, and then forms a 1- or 2-armed horizontal mother-gallery following the circumference of the stem along an annual ring; and on the upper and lower sides of this brood-gallery she alternately lays her 30 to 50 eggs in small niches. On hatching out in May the larvæ feed chiefly on sap oozing out from the walls of the main-gallery, and only when about full-grown bore short larval-galleries about

of an inch long and at right angles to the former. The main and subsidiary galleries therefore look like a single-pole ladder and its rungs (ladder-gallery), because the short larval borings are uniform in breadth. Pupation takes place

within these larval borings in June and July, in a cocoon formed of the bore-dust. The beetles emerge in July without special exit-holes, as they crawl back into the main-gallery and issue from the original entrance-hole formed in the sapwood. The walls of the galleries and the surrounding wood soon become blackened by fungi. A second brood is formed by the July beetles, which also emerge as beetles in October, and hibernate (along with stragglers of the first brood) in the stems till the following spring. Its generation is, however, usually double during the year.

Prevention and Extermination.Decoy-stems may be laid down as traps for ovideposition in summer, and then removed or charred before the beetles emerge in July. But by far the best thing is to remove winter-felled timber before the beetles emerge in spring. If that cannot be done, then the early removal of stems containing the eggs and the barking of logs are advisable, as the young brood is likely to die when the timber is dry.

Bostrichus (Xyloterus) domesticus, another wood-boring beetle closely related to the above species, is found in Britain in tree-stumps and windfall timber. It is about the same size as B. lineatus, but its wing-cases are bright yellow, and it is only found in broad-leaved trees (Oak, Beech, and softwoods), not in conifers.

7. The Oak-boring Bark-Beetle (Bostrichus (Xyleborus) dispar) is mostly to be found on Oak and Beech and on orchard-trees (chiefly Apple and Pear in Gloucestershire and neighbouring counties), but it also attacks most other hardwoods, together with Birch and Alder among softwoods. It is often very destructive to stout Oak saplings and transplants, which the larvæ can kill off rapidly. The beetle sometimes bores into and breeds in the stems of old Oak, Beech, &c., that have become somewhat sickly, and spoils the timber. It also bores into timber lying on the ground. Trees or saplings infested can be known by the bore-dust to be found on the ground below the bore-hole.

Appearance.—The beetles are black, with reddish antennæ and legs. The female is about g of an inch long and cylindrical, while the male is only about 1 of an inch long, ovoid, and convex. The wing-cases are well-rounded towards their apex, and have rows of deep punctures.

Life-history.—The beetles fly in May, when the females bore into healthy Oak and other saplings. The mother-galleries consist of (1) a short entrancegallery, (2) secondary-galleries, and (3) brood-galleries. There are no larvalgalleries, as the larvæ do not live by boring. The female usually enters just under a twig and bores upwards for a short way before tunnelling one or more secondarygalleries horizontally along one of the annual rings in the sapwood ; and from these the brood-galleries are bored longitudinally up and down the stem for about 1 inch or more. The latter resembles the larval-galleries bored in Spruce by Bostrichus lineatus, but are much longer. The eggs are laid in small clusters in these brood-galleries, and the larvæ which hatch out here feed on the exuding sap and on the fungus mycelium with which the mother-galleries soon become filled. The larvæ hatch out in June, feed on the sap, &c., for about 4 weeks, then pupate in July in the secondary-galleries for about 4 weeks. The beetles emerge in August, but hibernate in the galleries, and do not pair till their flight-time in the following May. The generation is therefore simple and annual.

Prevention and Extermination.-Saplings attacked should be cut back, and the infested parts burned. In orchards, the entrance-holes may be daubed over and filled with patent tar, or the beetles may be picked out with wire; but these measures are not practicable in the woods.

Bostrichus (Xyleborus) Saxesenii, a species closely related to the above, is also found attacking Oak in Scotland.

Fig. 151.

B. Proboscid Weevils or Long-snouted Beetles (Curculionida).- The main characteristic of weevils is the elongation of the head to form a snout (rostrum) by which the larger of them are easily recognisable. The great majority of Curculionidæ feed on broadleaved plants, and not a few of them on woodland trees; but the most destructive species are those which attack young conifer plantations.

In some cases the larvæ do damage by living in the interior of the plants and destroying their tissue, while in others very great injury is inflicted by the beetles devouring bark and cambium.

The large brown Pine-W il 1. The large brown Pine-Weevil (Hylo

(Hylobius abietis). bius abietis) is now the most destructive a. Beetle (natural size). insect in our British woodlands, although

b. Larva (natural size).

c. Pupa (natural size). the damage is only done during the adult stage (Fig. 151). It attacks young conifers in plantations and nurseries, and does most damage in 2- to 5. or 6-year-old plantations of Scots Pine, Sprnce, and Larch, though broad - leaved plants mixed with these are also

[ocr errors]

Fig. 152.

ty

Young Spruce plants gnawed by the large brown Pine-Weevil (Hylobius abietis), natural size.

a. Parts gnawed. b. Parts still covered with bark,

attacked, pieces of bark being gnawed away into the cambium (Fig. 152). It also attacks Weymouth Pine, Douglas Fir, Silver Fir, and Japanese Larch. Whole plantations may thus be totally destroyed. When the bark gets thicker and harder there is less risk of damage, so that plantations of about

ten years of age are comparatively safe from attacks. The injury is easily noticeable from the flow of resin. It does most damage in warm dry seasons. It sometimes attacks older trees, but the wounds soon get coated with resin and heal up. It is only found where conifer crops have been recently cleared.

Appearance.—This weevil is about } to : an inch long, and is stoutly built and convex in shape. It is deep-red to dark-brown or black in colour, and has a long thick proboscis. It is marked with clusters of yellow scales or hairs between the eyes, on the sides of the thorax and abdomen, and on the wing-cases. These small yellow patches look like cross-bands on the wing-cases, and are very prominent when the beetle emerges from the chrysalis, but they gradually get more or less rubbed off.?

Life-history.—The adult beetles live for two years or more, so that beetles which have recently emerged (with distinct markings on their wing-cases) and older beetles (with faint markings) that have been out for some considerable time, as well as larvæ in every stage of development, may all be found simultaneously.?

The beetles appear from April till early in June, when they crawl and fly towards freshly cleared coniferous falls, and deposit their eggs in the fresh sappy stumps and roots. As a rule, however, they do not fly much except in pairingtime. Pairing and reproduction are continued during summer as long as fresh stumps are available for breeding-places. The eggs are laid singly on roots from 1 an inch upwards in diameter ; but they are sometimes also laid in sawdust heaps near sawmills in the woods. On hatching out in about 4 weeks they at first bore only in the dead cambium, but later on also enter the sapwood and form long winding galleries, trending downwards and sometimes over 3 ft. long, at the end of which the pupal-chamber is formed. The yellowish-white larvæ have a large brown head, and are curved or bent by ventral contraction ;. they sometimes grow to about 1 of an inch long. In autumn, when full grown, they hollow out their pupal-chamber in the sapwood, and seal it up with bore-dust and wood-chips. Here they remain as larvæ till the following June, when they pupate and emerge as beetles about three weeks later. The whole development from egg to beetle thus occupies about 15 months. They find their most favourable breeding-places in autumn and winter, on falls of the mature conifer crops.

The beetles which emerge in July and only partially reproduce themselves are not so destructive as in the following spring. They begin to hibernate from about the end of August till autumn. They hibernate in thick grass or weeds, preferring the edges of woods adjacent to their breeding-places on the last fall of timber, or in the stumps of dead trees, or below timber lying on the ground, or in dead heaps of

It is distinguishable from the small brown Pine-weevil (Pissodes notatus) as follows:

[blocks in formation]

2

By von Oppen's observations, made on beetles confined under circumstances conforming as nearly as possible to natural conditions, it was found that this beetle can live up to two years, and that the same individuals can pair and lay eggs repeatedly. This function can be partly performed in one year, and resumed after hibernation. This explains the simultaneous appearance of recently emerged and older beetles, as well as of ova, young and full-grown larvæ, and chrysalides.

branches in the plantations. Early in autumn, when the females are laying their eggs, they often gather in large numbers in these places, whence they emerge in the following spring to pair again.

Though the boring of the grubs is not very injurious, the damage done by the beetles is often very serious. They gnaw off patches of soft bark from the stem and shoots of young Pine, Larch, and Spruce, and also of other conifers to a less extent, and sometimes even attack broad-leaved trees (especially Oak) mixed with those. Besides the bark, the beetle also eats into the cambial layer above the sapwood, stripping patches about the size and shape of a lentil; and these, becoming covered with resin, give a scabby appearance to the plants. Young plants attacked die off in large numbers, and plantations are often either ruined entirely or else need partial replanting.

Prevention and Extermination.-Clear-felling of mature crops over extensive areas stocked with Scots Pine and Spruce, which is often usual, and making large clearances side by side with the young plantations without grubbing up stumps and roots, where they cannot even be sold as fuel, must always favour the increase of this very destructive pest. Windfall timber and branches broken by heavy snowfall also favour their appearance, because great masses of stumps and roots offer the most favourable breeding-places.

The best means of preventing attacks is, of course (though it is not always practicable), to stub up all stumps and roots and sell them as fuel ; and wherever this can be done, there is little danger of the Pine-weevil doing much damage. Felling the timber by cutting through the main roots with an axe and pulling over the tree, though it does not leave so large a stump as in felling with axe and saw, is not sufficient to obviate danger, as even then many thick roots are left in the ground.

Where only a few of these weevils are noticeable, the stumps and roots may be stubbed at any convenient time. But when they are present in large numbers, the stumps should be used as traps for the eggs, and only stubbed up during the late summer, after the eggs have been laid, or at latest in the early spring.

For the protection of areas where young plantations are soon to be made, it is best to let the land lie fallow for one or for two years after a clear fall of timber.1 If the fall be at once replanted, then breeding-places and feeding-grounds are provided for the beetle on one and the same area ; and of course the danger will be all the greater if it has not been possible to root out the stumps (see vol. i. p. 462).

In trying to exterminate this pest, the beetle must, if possible, be caught in its breeding-places in the falls of the previous year. Narrow trenches about 10 to 12 inches deep may be dug round the last fall in early spring to prevent the beetles crawling from their winter quarters and laying their eggs in the fresh stumps. The trenches should be cut with smooth perpendicular walls, and holes about 1 foot deep should be dug here and there along the base, to serve as pitfalls and traps.2 As the beetles fly, especially during pairing-time, these trenches prove most useful in the summer of the second year, because they prevent newly-emerged beetles

1 Protection can also be obtained by allocating the annual falls of timber so that there is a suitable interval between two contiguous falls in the mature crop; and the longer the time between the planting of each two contiguous falls, the greater is the protection against this weevil (see also Part V., p. 257).

Experience at Scone (Perthshire) in 1899-1900 showed that the Pine-weevil can easily fly. Ditches were opened and filled with water, but this did not stop the beetles. On coming to the edge of the trench they spread their wings and flew across, going fully 10 to 12 yards. It was also found that putting stones or sods on the bark-traps only rot the latter in the damp climate of Perthshire. The best traps were there found to be pieces of fresh bark put inner side downwards on the ground, and renewed as soon as they get dry. If it is not convenient to replace them at once, then green sappy Pine twigs may be placed under the bark-traps till fresh bark can be laid down. The bark-traps must, of course, be examined frequently to catch the beetles.

« ForrigeFortsett »