other moths their habits are nocturnal. In June the female lays about 60 to 70 bright-green eggs on Pine-needles near the top of poles and at the extreme end of side-shoots. The caterpillars hatch out early in July (in about two to three weeks), and at once begin to gnaw the needles slightly, and afterwards bite them through about the middle, so that the upper half falls to the ground. Then they

Fig. 160.


Part of Pine branch, showing damage done by caterpillars of the Pine Geometer Moth (Fidonia piniaria). Here and there eggs can be seen on the needles.

feed on the lower half remaining. They can spin down to the ground on gossamer threads, and often descend thus before entering the pupal stage.

Pupation begins in October and continues till April. It takes place either under moss or dead needles, &c., or in the ground, the pupa lying free, and not enclosed in a cocoon. Caterpillars often lie on the ground waiting for the final moult, when they enter the pupal state. The pupa lie scattered about the whole area infested, and not merely near the trees on which they have been feeding.

The life-cycle is therefore as follows (MacDougall, op. cit., p. 113) :

November to April-Pupa under moss or dead needles, or in the ground. May-First moths appear (May 21). June-Flight of moths at its height. Eggs laid on the needles. July-Small caterpillars eating the needles. August and September—Growing caterpillars continue feeding. Their excrement noticeable under the poles and trees infested. October-Caterpillars, full-grown, descend the trees for pupation.

Protective and Exterminative Measures include shaking and tapping poles during summer in woods where span-worms have been seen, and herding swine in the woods during autumn and winter, to devour the pupa. The dead foliage may be raked in heaps and burned in autumn, when the caterpillars and chrysalides remaining on the cleared strips are either devoured by birds or perish from the winter cold. But this is only practicable on a comparatively small area.

Like the caterpillar of the Pine Beauty, the Pine Span-worm is very sensitive to changes in weather and temperature (dry warm seasons favouring increase, and cold wet seasons proving destructive), whilst numerous enemies prey on the caterpillars and pupæ, such as jays, thrushes, blackbirds, starlings, and tits. But when the moths increase in very large numbers, fungous epidemics usually soon attack the caterpillars and quickly kill them off.

Continental Note.-During the last 10 or 12 years Fidonia piniaria has proved very destructive in Germany, and is now classed along with the Pine moth, the Nun or Black Arches, and the Pine Owlet-moth, as among the worst enemies of the German woodlands. It did immense damage in the forests near Nuremberg in 1892-96, and in Friedesdorf in 1893-95, while more recently a series of dry summers led to very destructive attacks in the Letzlinger Heide, in North Germany, from 1899 to 1903. The hot dry summer of 1901, favourable to the insect, brought the culmination of the attacks; but the cold wet May and June of 1902, and the natural increase in parasitic Ichneumonidæ and Tachina that generally takes place after three years of any such insect calamity, stopped further damage.

Although the Pine-woods attacked were chiefly young crops, 20 to 40 years old, it was found that the portions twice stripped bare of foliage by the caterpillars were quite past saving, and had to be felled as soon as possible to keep down bark- and cambialbeetles (Hylesinini). The consequence was that in 1903 and 1904, in place of an annual fall of 2,220,000 cubic feet, 41,370,000 cubic feet had to be felled on about 21,500 acres, of which about 17,000 acres had been entirely denuded of foliage.

In combating this attack, it was found that the best plan was to try and destroy the pupa during winter. Grease-ringing the stems to prevent the ascent of caterpillars blown down by wind, &c., did not prove effective, as at most only about one-fourth of the caterpillars are thus brought to the ground. Driving in swine was out of the question throughout the whole of the area infested, as 50,000 would have been needed, so that this plan could only be adopted near villages. There, however, free pannage was given, and rewards to the swineherds. Hens were also bought and kept in the woods, and proved useful, although many of them died from diphtheria and soft crop, or were carried off by foxes, hawks, &c. Over large areas, however, the best means was found to be the removal of the soil-covering of dead foliage and moss, which could be sold locally as litter.

The Letzlinger Heide is a poor sandy stretch between Berlin and Hanover, where sylvicultural measures of prevention are hardly applicable. "One reads in text-books (1) underplanting; (2) mixed crops; (3) protection of this insect's enemies. But where can these be carried out? Protecting its enemies-of course!" The sandy soil is there generally too poor for mixed crops; but where Spruce and Pine were growing together, both were attacked, and also Juniper. The local experience there has been that "attacks of the Pine-looper cannot be effectually prevented by sylvicultural measures; but during the early stages the best means of exterminating the insect consist in removing the layer of soil-covering, and in herding swine and feeding hens where the pupæ are" (Nisbet, in Trans. Roy. Scot. Arbor. Socy., vol. xviii., 1905, p. 177).



D. Leaf-roller and Twig-twister Moths (Tortricida).

Moths with long, narrow, and somewhat rhomboidal wings, the fore pair generally brightly coloured; antennæ short, and filiform or bristly. Caterpillars with 16 legs (10 prolegs); usually with a horny shield on the prothorax, and a horny flap at the tail, and dotted with small warts bearing a few short hairs. They roll up the leaves of broad-leaved trees (whence the name), spin gossamer threads freely, and are active in habit. Pupa with rows of dorsal spines; pupation in a cocoon, mostly in the crowns of trees, but sometimes in the ground. Generation usually annual, sometimes biennial (Tortrix resinella).


Fig. 161.

1. The Oak Tortrix or Leaf-roller (Tortrix viridana) is a pretty little green moth, which every few years defoliates the Oaks in many parts of the country. The Oaks in Windsor Park, for example, were damaged badly in 1902. The caterpillars strip the Oak-foliage entirely, and then attack other broad-leaved trees when their natural food is insufficient in quantity for them. It lives almost exclusively on middle-aged and old Oaks (Fig. 161), occasionally swarming in great numbers over extensive areas, entirely devouring the Oak foliage, checking the growth of the tree, and preventing the ripening of acorns. Owing to the Oak's strong recuperative power, and its large store of nutrient reserves, the damage is not usually lasting. As the eggs are laid on buds and young twigs, the caterpillars always begin to feed near the top of the tree and move downwards, totally defoliating the tree. The foliage can, however, to a certain extent, be replaced when the midsummer flush of leaves takes place.


The Oak Leaf-roller Moth (Tortrix viridana)-natural size.

Appearance. This moth has a wing-span of less than 1 inch. The fore wings are pale bright-green, with a whitish or yellowish-white fringe round the lower edges, and with lightgrey hind-wings edged with white or greyishwhite.

The 16-legged caterpillar (10 prolegs), which is about an inch long when full-grown, is at first grey-green, then becomes dark yellowish

a. Moth.

b. Caterpillar spinning itself down by green, with a black head and small black tuber

a gossamer thread.

c. Rolled-up Oak-leaf in which the caterpillar pupates.

cular warts on the back, which bear a few fine hairs.

d. Pupa.

The pupa is blackish - brown, slender, and less than an inch long.

Life-history. The moth flies late in June and early in July. The female lays her eggs either singly or in small clusters on the buds then being formed in the crowns of Oak-trees. The caterpillars hatch out when the Oak-leaves flush in the

following May. They feed on the leaves, and spin threads to drop to lower foliage when changing their feeding-ground. Early in June they begin to pupate either in remnants of leaves rolled together (hence their name), or in bark-fissures, &c. When nearly full-grown the caterpillars can spin themselves down to lower branches by gossamer threads to continue their feeding, and to find suitable places for pupating. About three weeks later the moths emerge, pair, and lay their eggs. The generation is therefore simple and annual.

Preventive and Exterminative Measures can hardly be applied against this pest, because the whole life of the insect is spent on the tree, and the females can fly and distribute their eggs far and wide. When late frosts nip the young Oak foliage during years when the caterpillars abound in large numbers, these are starved to death. Birds form the best natural check, and should be encouraged to breed in nesting-boxes. Many birds feed on the caterpillars, and during the winter many ova are also no doubt destroyed by starlings, thrushes, sparrows, tits, woodpeckers, &c.

2. The Pine-shoot Tortrix or Pine Twig-twister, Tortrix (Retinia) buoliana. Though a small moth, this common species in Britain may sometimes become a very dangerous pest in Pine-woods. When the moth swarms in large numbers, young Pines are attacked year after year, and of course become sickly and stunted. Attacks are mainly confined to Scots Pine (less frequently on Weymouth, Austrian, and Corsican Pines) of 5 to 12 years old growing on poor soil with a warm southerly exposure.

Appearance. The moth has a span of less than 1 inch. The narrow forewings are reddish-yellow, with six or seven broad, wavy, silvery-white, transverse bands, tinged bluish about their middle, and with greyish-white edging; and the hind-wings are glossy dark-grey, while both pairs have light-grey or greyish-white fringes. Below, the wings are glossy dark-grey, with yellowish-red and white spots near the upper edges.-The 16-legged caterpillar (10 prolegs) is about an inch long when full-grown, and is light-brown, with a glossy black head and thorax.

The pupa is dirty yellowish-brown, and about of an inch long, and has a row of fine dorsal prickles.

Life-history. The moth flies in the evening during the whole of July, and in the daytime it is hidden among the needles and shoots of young Pines, with wings ranged over each other like roof-tiles. The female lays her eggs singly on the terminal buds of young Scots Pine shoots, in plantations of 5 to 12 years old. On hatching out in August the caterpillars at once begin to bore, but are so small that the damage is hardly noticeable during the first autumn. In September they hibernate in the buds, and in the following spring the caterpillar, now larger, stronger, and more active, does greater damage; but the bud develops partially before the shoot dies in consequence of being hollowed out. As a rule the terminal bud is hollowed out first, and then the side-buds forming the whorl. Should any of these escape injury it becomes the leading-shoot. But in such a case it often happens that a damaged shoot bends downwards before beginning to grow upwards; and such a bend at the damaged place is still recognisable even when the tree is mature. Pupation takes place at end of May or in June at the base of the hollow tunnelled in the shoot. The moth emerges about four weeks later.

Preventive and Exterminative Measures.-The only way of getting rid of this pest is to break off and destroy, from May till the middle of June, all shoots infested, and thus destroy the caterpillars and pupae; but they must be looked for below where the twig breaks. Shoots attacked are easily seen.

3. The Pine-bud Tortrix, Tortrix (Retinia) turionana.—Like the Pineshoot Tortrix, the attacks of this moth are practically confined to young Scots Pine (and occasionally also other Pine) woods of from 5 or 6 to 15 years of age. It is, however, a less common species throughout Britain.

This moth seldon occurs in such large numbers as the Pine-shoot Tortrix; and as it does not often happen that all the side-buds forming the whorl are injured, one of these generally assumes the place of a leading-shoot, thus materially minimising the actual damage done.

Appearance. The Pine-bud Tortrix very much resembles the Pine - shoot Tortrix, but is smaller, having a wing-span of less than of an inch. The forewings are ruddy-brown, with wavy leaden-grey transverse bands and patches, and fringed round the edge with dark leaden-grey; the hind-wings are grey, with greyish-white fringes. Underneath, the fore-wings are blackish-grey, with patches of red towards the tip, and of greyish-white towards the upper edge; while the hind-wings are greyish-white underneath, but darker towards the upper edge.

The 16-legged caterpillar is less than an inch long, and both caterpillar and pupa closely resemble those of Tortrix buoliana.

Life-history. The moths fly about the end of May and in June, and lay their eggs singly on the terminal buds of young Pine-shoots, into which the tiny caterpillars bore when they hatch out. During the autumn and the following spring they hollow it out, so that the young shoot withers, becomes blackish-grey, and dies. About the end of April or in May the caterpillar pupates within the hollowed bud, which it fills with the fine threads of its cocoon. From this the moth emerges late in May or early in June.

Preventive and Exterminative Measures consist merely in careful revision of the thickets during April and early in May, and breaking off and destroying buds infested. They are easily known by their small size and dark colour.

4. The Pine Resin-gall Tortrix, Tortrix (Retinia) resinella, is very common in Central and Northern Scotland, where damage is often reported from the caterpillars boring into shoots below the whorl of buds, and living inside the gall formed by the outflow of resin. Their presence is recognisable by the resinous outflow, the stunted side-shoots, and their liability to break off when touched. Branches attacked assume a twisted appearance.

Appearance. The wings of this small moth have a span of hardly of an inch. Head, body, and fore-wings are dark-brown or slate-coloured, with a coppery sheen. The upper wings have silvery or lead-grey transverse stripes, and a blackish feathery fringe, while the lower wings are dark brown-grey with light-grey fringe; and in both pairs the under side is dark brown-grey.

The 16-legged caterpillar is less than an inch long, and yellowish-brown in colour, with a light-brown head. The pupa is of an inch long, and very dark, almost black.

Life-history. This insect is remarkable in having a two-yearly generation, which is uncommon among Lepidoptera. The moths appear in May, and the female lays her eggs singly beneath the whorl-buds of young Pines, and chiefly on the side branches. The caterpillar hatches out a few weeks later, and bores through the bark into the soft shoot. Resin flows from the wound and forms a small soft gall which grows to about the size of a pea, and in which the small, 16-legged, worm-like caterpillar hibernates during the following winter. In the second year the caterpillar resumes feeding, and the gall increases, with thick walls of resin, to the size of a cherry or a small nut, while internally it exhibits a well-marked partition formed by the gall of the previous year. The shoot is hollowed to the pith and enclosed within the resin-gall. In April of the second year the caterpillar pupates within the gall, and in May the moth emerges from the gall. The generation is therefore biennial.

« ForrigeFortsett »