« ForrigeFortsett »
Prevention and Remedy.-- This Tortrix, on the whole, does not do very much damage, because the leading-shoots are seldom attacked, and are not always killed in consequence. But when allowed to multiply greatly, and especially in young woods growing on inferior soil, the damage may often be quite enough to make it advisable to collect the galls and destroy them while they still contain the caterpillars (before the end of the second autumn).
The chief danger from this insect is that in woods attacked by it there is always a chance of the two more injurious species, T. buoliana and T. turionana, also attacking the crops.
E. Leaf-mining Moths (Tineido).
Moths with long, narrow, pointed wings having long fringes ; antennæ filiform or silky and brush-like, seldom pectinate. Caterpillars 16-footed, usually with 10 prolegs. Pupa thin and hairless, with long wing-cases extending almost to the tip of the tail. Generation annual.
1. The Larch Mining-Moth, Tinea (Coleophora) laricella.—This is a very injurious insect throughout the whole
Fig. 163. of Britain, and besides the great damage it directly occasions by de
a foliating young Larchwoods, the wounds made offer entranceholes for the destructive
6 canker-fungus. There is now
a year when the pest is not reported from some part or other of the British Isles (Figs. 162, 163), but the worst The Larch Mining-Moth
(Coleophora laricella). recent attacks have
a. Moth (magnified three times). perhaps been those in
b. Larval covering formed of leaf. and around Gloucester case (magnified three times). shire.-Experiments in
c. Caterpillar (magnified three
times). Germany show that
d. Pupa (magnified three times). the caterpillars burrow readily into the needles of the Japanese Larch (L. leptolepis), but the long soft needles of the youngest shoots are too large to be conveniently used for Showing the Larch Miningmaking their larval cases ; while the foliage of
Moth at work, and the
kind of damage it does. the Siberian Larch (L. siberica) seems to disagree
a. Larvæ in leaf-cases. with them, and to make them sicken and die.
b. Naked larvæ.
6. Needles attacked and holAppearance.- Moth ashy-grey or greyish-black and
lowed out. lustrous, with a wing-span of less than an inch. Caterpillar with 16 feet (10 prolegs), dark ruddy-brown, and about } of an inch long. Pupa also about } of an inch long, dark-brown, narrow, and covered with fine bristly hairs.
Life-history. The moth flies in the daytime about the end of May and in June. The female lays her small round yellow eggs (changing to grey in about a week) singly on Larch needles, usually in plantations of from 10 to 40 years of age, and chiefly on the lower branches of 10- to 14-year-old poles freely exposed to the sunlight. But older woods and also saplings and young plants are also sometimes attacked when the moths swarm in great numbers. The caterpillar hatches out in three to four weeks, bores its way into the needle, eating out the contents, and using the empty leaf-case as a protective covering, in which, when full-grown in September, it hibernates, the empty leaf-case now becoming a little yellowishbrown sack, firmly fastened to twigs, bark - fissures, &c. Next spring it again feeds on the new needles, but carries its sack about with it, and finally pupates in this (Fig. 162b). The needles attacked by the young and the old caterpillars at once turn yellow and withered as if frost-bitten, and the damage is often so serious that entire defoliation takes place, especially in the case of young Larch-trees near the edges of green lanes, &c. Whole plantations sometimes look as if their foliage had been badly nipped by late frost. As new needle-tufts are formed in the centre of the damaged rosettes, however, they gradually recover and develop short shoots which take the place of the long shoots destroyed.
Damage of this sort is often repeated year after year on young Larch growing near the edges of plantations, and they gradually sicken and die in consequence.
Preventive and Exterminative Measures.-Small birds like tomtits, and various Ichneumonide, prey on the caterpillars. Late frosts and heavy rainfall at the time of swarming kills off many of the moths. The only active measures that can be taken are to thin Larch-woods in winter or early spring, and remove the thinnings before the moths emerge in May. Pruning the lower branches of Larch-trees in infested areas removes material specially attractive as breeding-places. Mixed woods are far less exposed to attacks than pure Larch plantations.
F. Wood-boring Moths (Cosside).
Moths with thick bodies covered with short hairs, and large wings; antennæ brushlike or pectinate. Caterpillars 16-legged, large and round, either smooth or with a few scattered hairs. Pupo large and long, with rings of spinal processes on the abdomen ; cocoons formed of bore-dust and wood-chips. Generation two or three years.
This family includes two genera, the caterpillars of which do a very considerable amount of damage throughout Britain among orchard- and broad-leaved trees, though seldom attacking any conifer. They make timber often useless for technical purposes, by riddling it with big holes.
1. The Goat-Moth (Cossus ligniperda).—This large moth (Fig. 164), so named from the goat-like smell of its caterpillar, also called the "Augur-worm" in Scotland and the “Carpenter-worm” in England, is one of the worst of enemies to Elm, Oak, Willow, Poplar, Ash, Alder, Birch, Beech, and Lime, and in orchards to Apple, Pear, and Walnut. The caterpillars drill holes through the bark into the timber, and finally throw the trees into a sickly condition. It is most common in the warmer parts of England, but is also found all over Scotland and Ireland. As the holes are large, trees attacked are often killed outright. The caterpillars are often found deeply embedded in large Willow and Poplar, as they prefer to bore into softwoods; and in many cases such trees become riddled with holes. But they also bore into the hardest wood, and are common in Oak- and Elm-trees. Badly-bored trees are often thrown during storms. Unless exterminative measures be adopted,
trees attacked become regular breeding-places for this insect. Badly infested trees " bleed” freely, and emit the characteristic goat-like odour.
Appearance. — The moth has a span of about 2} to 3 inches for the male, and about 3 to 3} or nearly 4 inches for the female. The fore-wings are greyish-brown, mottled with ashy-grey marks, and with numerous irregular dark-brown streaks and marks; the hind-wings are ashy-grey to greyish-brown, and the thorax is
densely haired, with a blackish band across it behind, and brown and grey in front. The large heavy abdomen is long and blunt, and with dusky - brown and grey bands. The 16-footed caterpillar is, when full-grown, about 3 to 3} inches long. It is at first reddish-yellow, and turning brownish-red later on, with brown head and shield, darker above than below, naked, and having an offensive goat-like smell. The pupa is thick and ruddy-brown, and has rings of prickles on the abdominal segments.
Life-history. The moths fly and pair in June and July, when the female lays her eggs, to a total of about 25, in bark-crevices of Oak, Elm, and most softwoods, usually on the lower part of a tree-trunk. The caterpillars hatch out in July, and at first feed under the bark, but soon bore into the solid wood, where they form long tunnels, in which they live for two to three years. Sometimes the caterpillars leave the trees and crawl about on the ground. When mature they usually pupate just inside the entrance to their burrows (and sometimes in the ground), the large reddish brown pupa lying in a cocoon of rough wood-chips. Previous to the moth emerging in June or July, the pupa pushes its way partly out of the tree. The life-cycle extends to two or three years.
Preventive and Exterminative Measures.—Little can be done to prevent attacks of the Goat-moth. Trees attacked show, even at an early stage, bore-dust and excrement at the opening of the bore-holes. Syringing the holes with carbolic acid and other poisonous substances has been tried, but without much success, as the caterpillars are usually too well protected by bore-dust and wood.chips for the poison to reach them. Putting bits of cyanide of potassium in the holes has, however, been found successful. Badly infested trees should be felled, and branches cut, and the caterpillars destroyed. The lower parts of the trunks of trees attacked may be smeared early in June with a thick dressing of mud and paraffin to prevent egglaying. Bats, owls, goat-suckers, titmice, and other small birds are useful in clearing off the eggs, and woodpeckers extract the caterpillars from infested trees, while many birds feed on the moth itself.
The following is a recipe quoted by Nitsche as in use on the Continent, with good results not only against Cossus ligniperda, but also other insect enemies of the woodlands (MacDougall, in Trans. High. and Agri. Socy. Scot., vol. xii., 1900, p. 297):
Infuse 5 lb. of tobacco in half a pailful of warm water, and allow this to stand for twenty-four hours ; then strain. Mix the infusion with half a pailful of bullock's blood, and add one part of slaked lime and sixteen parts of cow's dung. Allow this mixture to remain for a short time in an open cask so that it ferments, and stir several times daily. Clean the base of the stem, removing some of the earth at the bottom, and paint on the composition. Repeat the painting three days in succession, and a crust is formed on the stem which rain does not wash off, and which does not harm the tree.
2. The Wood Leopard-Moth (Zeuzera æsculi) also damages timber technically like the Goat-moth. It chiefly attacks young stems of Maple, Sycamore, Ash, and Lime among forest-trees, but in orchards it is found on Pear, Cherry, Apple, and Plum trees. Although called æsculi, it attacks other woodland species as well as orchard-trees, far more frequently than the Horse-Chestnut.
Appearance. It is only about two-thirds of the size of the Goat-moth. The wings are almost white, with numerous round black or steel-blue irregular spots ; and there are six similar spots in two rows on the upper part of the body. The abdomen is dull - white or grey, striped alternately with blue - black and white bands. The caterpillar is yellowish, with little black warts, and nearly 2 inches long when full-grown. The pupa is bright brown, nearly an inch long, and has rows of sharp spikes along its back, which serve to retain the empty cocoon in the mouth of the gallery during the emergence of the moth (see below).
Life-history.—The moth flies from June till August, and lays large numbers of orange-coloured oval eggs on the stems and branches of trees. In a few days the acterpillars hatch out and bore into the bark. They remain feeding in the sapwood till winter, when they bore deeper, tunnelling upwards into the stem. They continue in the larval state for two years, feeding continuously. In May or June of the second year they return to near the bark and pupate within the sapwood,
to emerge as moths in June or later. Its generation is therefore biennial. The bark just over the pupal-chamber is left so thin by the larva that the pupa can easily force itself through it, and the empty cocoon is found protruding from the hole after the moth has emerged.
Preventive and Exterminative Measures. As for the Goat-moth.
G. Clearwing-Moths (Sesiida).
Moths with narrow and more or less transparent wings (like Hymenopterous insects) and thickish body; antennæ brush-like. The moths fly about in the daytime during bright sunshine. Caterpillars 16-footed, with 10 prolegs; yellowish-white, cylindrical, and sparsely sprinkled with fine hairs. Pupa with rings of prickly spines on the abdomen, in a cocoon formed bore-dust and wood-chips. Generation, two years.
1. The Hornet Clearwing-Moth, Sesia apiformis (Trochilium apiforme), the largest and most important of this group, damages the butts of young Poplar stems up to about 20 years of age (and especially Black Poplar and Aspen) in much the same way as the Poplar Longicorn and the Goat-moth. The caterpillar feeds for two years, and often riddles with holes the butts of Poplars. It does most damage in avenues and nurseries.
Appearance.—The moth has transparent wings, with rust-red edges and veins, and a span of about 14 to 14 inch. The caterpillar is rather flat, dirty- or yellowish-white, with a large brown or red-brown head, and a dark dorsal line ; it has 16 feet (3 pairs of true legs, and 5 pairs of suckers or prolegs). Its head and legs easily distinguish it from the larva of the Poplar Longicorn, along with which it is often to be found at work (compare Fig. 157, p. 100). Pupa brown, with prickly dorsal spines on the abdomen and at the tail-end.
Life-history. The moths fly in June and July, and lay their brown eggs in bark-fissures near the base of Poplar stems. The caterpillars hatch out in July and August, bore into the stem, and live there for two winters, then come out and pupate, either near the mouth of the bore-hole or else on or near the ground in cocoons formed of bore-dust and wood-chips. The moths emerge in June, the generation thus extending over two years.
Preventive and Exterminative Measures.—Catching and killing the moths on the Poplar stems (June, July); cutting and removing infested poles ; smearing with patent tar or cart-grease the butts of young Poplars where the pest is known to exist ; and as for Poplar Longicorn (see p. 100).
Several other Clearwing-moths perforate the branches of deciduous trees in a similar way to the above. Such are the Red-belted Clearwing (Sesia culiciformis), which attacks the Birch ; the Red-tipped Clearwing (S. formicæformis), common in Osier-beds; and the Hornet Clearwings (S. bombiciformis, and S. tipuliformis) common to various kinds of broad-leaved trees.
III. Membrane-winged Insects (Hymenoptera).
The main distinguishing characteristics of this order are the four transparent wings, and the facts that the anterior and posterior wings are hooked together during flight, and that the females have an appendage at the tail in the form of a sting, awl, or ovipositor. Several of them are destructive to trees.
A. Sawflies (Tenthredinida.— These are transparent-winged insects, whose females lay their eggs in holes sawed in leaves by means of an ovipositor (hence "sawfly ").