Wood Leopard Moth — (Zeuzera Æsculi)
(Very destructive to trees, particularly around London)
Wood Leopard Moth (Zeuzera æsculi).—The caterpillar of this beautiful moth is very destructive to the beech, ash, birch, elm, walnut, privet, etc., which it bores into, eating and living on the wood. Usually young trees or the branches of old specimens are attacked, and the tunnelling is confined in the former either to the pithy centre or the soft wood near the bark. The moths appear about mid-July, and the female, by piercing the bark with her powerful ovipositors, deposits her eggs, one in each hole. Three years are required for the caterpillar to arrive at maturity when it is nearly 2 in. long. Both in form and colour the leopard moth is particularly elegant, the head and thorax being covered with a thick white pile, the body with a black down, fringed with white at each joint. The wings are white with yellowish-brown veins, a row of rounded bluish spots running between every two.
By stuffing a piece of tow in gas tar, or placing cyanide of potassium in the hole and closing the aperture, the caterpillar may be overpowered and destroyed.
A bent wire has often been successfully used in dislodging the caterpillar.
The Holly Fly (Phytomyza aquifolia).—The foliage of the holly is frequently very much disfigured by the grubs of the holly fly, which burrow beneath the upper skin of the leaves, feeding on the internal substance. This imparts a blistered and discoloured appearance, which, in the case of ornamental varieties, is anything but desirable. Probably no great damage to the infested trees is brought about, but the wholesale destruction of the leaves, as is often the case, cannot but weaken the plant.
In May and June the flies make their appearance, and lay their eggs beneath the upper skin of the leaf, from which the grubs, about one-fifth of an inch long, are hatched. These work their way beneath the skin of the leaves, forming small tracks of a more or less circular shape, thus causing the large and unsightly blisters. They quit the leaves about March, by making small holes in the skin of the leaf, and afterwards become chrysalides. The fly is small and inconspicuous.
Picking off and destroying affected leaves, or crushing the grub by pinching the blisters are the only ways of lessening the attacks.
The Oak Leaf Roller Moth (Tortrix viridana).—The widespread destruction caused to oak-woods in almost every part of the country by the caterpillars of this little moth would seem to be on the increase from year to year. But it is not the oak alone that suffers, for numbers of the hornbeam and beech are in an equally pitiable condition. Having closely watched this insect for several years, mainly with the view of striving to keep it in check or devise some means of destruction, I have come to the conclusion that a few individual trees may, at considerable expense, be rid of the pest, but in the case of whole woodlands artificial treatment is quite out of the question. Many observers are under the impression that the caterpillar is most abundant where the trees grow closest together, and when we consider that both wind and rain destroy numbers of these, the fact of isolated trees, which, consequently, are most exposed to storms, being comparatively free from attack is not to be wondered at. So far as we know at present, the only way to diminish in any appreciable degree the numbers of this insect is by encouraging as much as possible its enemies.
The rook, jackdaw, starling, thrush and sparrow help immensely in destroying the caterpillars, and the occupants of a rookery will frequently in a few hours clear the pest from the trees over a considerable area of woodland. The same has been noted with regard to the starling, and I have frequently seen the trees over an infested area almost black with this particular bird when in the act of feeding on the caterpillars.
In support of this recommendation it may be stated that insects are far less numerous in the forests of St. Germain, Senart and Fontainebleau than in the Bois de Boulogne, where, of course, small birds are scarcer.
Sometimes with the oak leaf roller moth its excessive number proves the means of its extinction, the foliage being devoured before the caterpillars are fully fed; while, as is usual at the season of attack, parasitic flies and ichneumons destroy them wholesale, and a box of caterpillars sent to me the other day revealed the fact that each one had succumbed to the attacks of one of these enemies.
The life history of this moth is full of interest, and the curious manner in which it rolls up the leaves is well worthy of study.
The Felted Beech Coccus (Cryptococcus Fagi).—Judging from the numerous specimens of the beech coccus that are being forwarded to me for identification, and the inquiries as to how this insect pest may be dealt with, its presence in almost every part of the country is indicated. It was only in 1862 that Dr. Balfour reported the presence of this coccus in Scotland, and I remember well how the beautiful beech hedges on the Penicuik Estate, Mid-Lothian, were ravaged by the insect in 1875. In Germany, however, the beech coccus was noticed as early as 1849. It is probable that the beech coccus also extends to the Weymouth pine, as at Keston, Lord Derby’s estate in Kent, several of these trees were badly affected with an insect that appeared to me identical with this pest, and other instances of the Weymouth pine being similarly attacked have been recorded. Since the appearance of the insect in Scotland it has spread southwards rapidly, but it is only of late years that its ravages have been felt severely, and that owners of woodlands have been driven to do everything in their power to combat its injurious effects. I think I have nowhere seen the insect so abundant as on the Burnham beeches, which I visited in company with several members of the Royal Horticultural Society at the request of the Lord Mayor and the Corporation of the City of London. Here, speaking broadly, all the trees are affected in a greater or less degree, independent altogether of the age or health of the trees.
Amongst the beautiful beech woods of Hertfordshire, where the timber produced commands a higher price than that from any other station in Britain excepting the Chiltern Hills, the trees are suffering severely. After a careful inspection of many beech woods, I am at a loss to account for the spread of this insect. Usually, in the case of injurious forest insects, the presence of dead and dying wood and the general health of the plantations have much to do with the attack, but this would not appear to be the cause in the case of the beech coccus. Even old and diseased trees do not appear to suffer more than the young and healthy specimens, and at Burnham some of the youngest and fastest growing specimens were by far the worst affected, appearing in parts as if coated with drifted snow. Neither would soil appear to have anything to do with the spread of the insect, as on chalky, sandy and loamy soils, as well as on shale rock, the trees are all more or less affected. I cannot say that unhealthy trees are more liable to be attacked than vigorous ones, for I have observed diseased trees to be sometimes quite free from the coccus, whilst healthy specimens in the immediate neighbourhood were badly infested. This was particularly noticeable on some park trees on two estates that I visited lately; in each instance the majestic boles rose to a height of fully 90 ft. and contained about 100 cubic ft. of wood. At one time I had an idea that beech trees when grown too thickly were most liable to be attacked, but more extensive observations have disproved the hypothesis. By some it has been suggested that the drainage of ground on which the beech is growing will facilitate the spread of the insect by bringing about an unhealthy state of the trees. To some extent this has been noticed at Burnham, and particularly in Gloucestershire, where a lake had been formed contiguous to a beech plantation. In another instance that came under my notice the burrowing of rabbits to an unusual extent was blamed for the appearance of the insect and the gradual death of the trees, the soil in this case being sand and gravel. It is a strange fact, too, that a badly infested tree may be standing amongst others that are perfectly free from the attack. Under a magnifying glass the insect appears of a yellowish colour, irregularly globular in shape, and almost transparent. It is thickly covered over by a secretion from the body, which looks like fine waxen-white threads or cotton wool, which effectually screens the insect from observation. With its proboscis it sucks up the juices, which are readily reached through the thin, smooth bark. When badly attacked, the foliage becomes meagre and has a burnt appearance, then the tips of the branches, and finally whole branches die off. Afterwards the bark becomes dry and cracks, usually longitudinally, falling off in flakes with the death of the tree. The timber of trees that have been killed by the coccus is dry, short-grained, and by no means comparable with that of healthy specimens. From whatever cause, the presence of the insect in our plantations is much to be deplored, and already many fine old trees in different parts of the country have succumbed to the attack. It is a curious fact that certain trees fall victims to the attack of this insect very rapidly, often in the short space of two years, while others of equal age and vigour, and, as far as can be seen, similarly situated, live for many years. Fully grown trees are, in my opinion, more liable to be killed quickly than younger specimens.
As regards remedies, these can only conveniently be applied to single specimens and are scarcely practicable on a large scale. That success has, however, attended the application of certain remedies I am quite convinced, for several valuable ornamental trees on a lawn in Buckinghamshire that were badly affected by the pest are now, twelve months after being treated, quite free from the insect, and do not appear to have suffered in consequence. In this case the remedy was simple, and consisted merely in scrubbing the tree stems where affected with a stiff brush dipped in an emulsion of soft soap, this being rubbed well into all crevices of the bark. Only one application was given, but as the trees were nearly 100 ft. high with many large limbs, which also showed the presence of the coccus, the work took a considerable time. However, the results well repaid the expense of labour. Another excellent remedy is to mix together equal portions of paraffin and soft soap, and when required for use add twenty times their bulk of hot water, stirring all well together. This may be applied either with a scrubbing brush or syringed on to the affected parts. Other measures of a more drastic nature have been found to be beneficial, but those given are probably the simplest and best. Three or four handfuls of lime to a bucket of water is an excellent application, the only drawback being the unpleasant colour imparted to the trees. This is a simple remedy, and may be applied with a painter’s or scrubbing brush. It has saved many trees on an estate near London.
Wireworms.—These occasionally do a great deal of damage in beds of seedling trees, particularly conifers, and in some instances they attack and destroy the seeds before germination. In the case of young conifers they are gnawed completely through just above or at the ground level, the beds in many instances being strewn with the cut-over plants. Abies nobilis and A. Nordmanniana suffer to a great extent, and I have frequently been at my wit’s end to put a stop to the repeated depredations. In the case of a newly-formed nursery or freshly-made-up seed-beds the attack of the wireworm is always most pronounced. In the case of fresh nursery ground, paring off and burning a couple of inches of the top soil in the autumn has been attended with excellent results, as has also dressing the ground with gas lime. When seedlings are attacked, hand-picking, with the use of sliced carrots, mangold or potatoes, varied with pieces of oilcake as a bait, are to be recommended. Dressing the seeds with red lead is very advantageous to prevent birds and mice from attacking freshly-sown quantities. Injury from wireworm is not likely to cause any serious consequences after the first year’s growth of the plants, especially if the ground has been kept clean and free from weeds during the egg-laying season in June.