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 ECONOMIC ENTOMOLOGY 635 the females producing living young without the agency When required for use, 1 lb of the compound is dissolved in 5 to of a male. Males in nearly all species appear once a year, 10 gallons of warm water. These two washes are essential to the well-being of every when the last female generation, the ovigerous generation, in all climates. Not only can we now destroy larval and is fertilized, and a few large ova are produced to carry orchard adult insects, but we can also attack them in the egg stage by on the continuity of the species over the winter. Some the use of a caustic alkali wash during the winter; besides aphides live only on one species of plant, others on two or destroying the eggs of such pests as the Psyllidce, Eed Spider, and more plants. An example of the latter is seen in the Hop some Aphides, tliis also removes the vegetal encumbrances which shelter numerous other insect pests during the cold part of the Aphis (Phorodon humuli), which passes the winter and lives year. Caustic alkali wash is prepared by dissolving 1 lb of crude on the sloe and damson in the egg stage until the potash and 1 lb of caustic soda in soft water, mixing the two middle of May or later, and then flies off to the hops, solutions together, adding to them £ lb of soft soap, and diluting where it causes endless harm all the summer (Fig. 5); it with 10 gallons of soft water when required for use. Another insecticide for Scale Insects is resin wash, which acts flies back to the prunes to lay its eggs when the hops are approved in two ways : first, corroding the soft scales, and second, fixing the ripe. Another Aphis of importance is the Woolly Aphis harder scales to stop the egress of the hexapod larvte. It is pre(Schizoneura lanigera) of the apple and pear: it secretes pared as follows:—First crush 8 lb of resin in a sack, and then tufts of white flocculent wool often to be seen hanging in place the resin in warm water and boil in a cauldron until thorpatches from old apple trees, where the insects live in the oughly dissolved ; then melt 10 lb of caustic soda in enough water to keep it liquid, and mix with the dissolved resin ; rough bark and form cankered growths both above and warm keep stirring until the mixture assumes a clear coffee-colour, and for below ground. Aphides are provided with a mealy skin, ten minutes afterwards ; then add enough warm water to bring the which does not allow water to be attached to it, and thus whole up to 25 gallons, and well stir. Bottle this off, and when insecticides for destroying them contain soft soap, which required for use dilute with three times its bulk of warm soft water, spray over the trees in the early spring just before the buds fixes the solution to the skin; paraffin is added to corrode and burst. For mites (Acari) sulphur is the essential ingredient of a the skin, and the soft soap blocks up the breathing pores spray. Liver of sulphur has been found to be the best form, especially when mixed with a paraffin emulsion. Bud Mites and so produces asphyxiation. Amongst Orthoptera we find many noxious insects, (Phytoptida, Fig. 6) are of course not affected. Sulphur wash is notably the Locusts, which travel in vast cloud-like armies, clearing the whole country before them of all vegetable life. The most destructive locust is the migratory locust (Locusta migratoria), which causes wholesale destruction in the East. Large pits are dug across the line of advance of these great insect armies to stop them when in the larval or wingless stage, and even huge bonfires are lighted to check their flight when adult. So dense are these “ locust clouds ” that they sometimes quite darken the air. The commonest and most widely distributed migratory locust is Pachytylus cinerascens. The mole cricket (Gryllotalpa vulgaris) and various cockroaches (Blattidce) are also amongst the pests found in this order. Of Neuroptera there are but few injurious species, and many, such as the lace wing flies (Ilemerobiidce), are beneficial. The Treatment of Insect Pests.—One of the most important ways of keeping insect pests in check is by “spraying” or “washing.” This method has made great Fig. 6.—Bud Mites (Phytoptidce). A, currant bud mite (Phytoptus ribis); B, nut bud mite (P. avellance). advances in recent years. All the pioneer work has been done in America; in fact, until the South-Eastern Agri- made by adding to every 10 gallons of warm paraffin emulsion cultural College undertook the elucidation of this subject, or paraffin-naphthalene-emulsion 7 oz. of liver of sulphur, and little was known of it in England except by a few growers. stirring until the sulphur is well mixed. This is applied as an ordinary spray. Nursery stock should always be treated, to kill The results and history of this essential method of treat- scale, aphis, and other pests which it may carry, by the gas treatment are embodied in Professor Lodemann’s work on the ment, particularly in the case of stock imported from a foreign Spraying of Plants, 1896. In this treatment we have to climate. This treatment, both out of doors and under glass, is bear in mind what the entomologist teaches us, that is, carried out as follows :—Cover the plants in bulk with a light gastight cloth, or put them in a special fumigating house, and then the nature, habits, and structure of the pest. place 1 oz. of cyanide of potassium in lumps in a dish with water For insects provided with a biting mouth, which take nourish- beneath the covering, and then pour 1 oz. of sulphuric acid over ment from the whole leaf, shoot, or fruit, the poisonous washes it (being careful not to inhale the poisonous fumes) for every used are chiefly arsenical. The two most useful arsenical sprays 1000 cubic feet of space beneath the cover. The gas generated, are Paris green and arsenate of lead. To make the former, mix hydrocyanic acid should be left to work for at least an hour before 1 oz. of the Paris green with 15 gallons of soft water, and add the stock is removed, when all forms of animal life will be 2 oz. of lime and a small quantity of agricultural treacle; the destroyed. latter is prepared by dissolving 3 oz. of acetate of lead in a little For spraying, proper instruments must be used, by means of water, then 1 oz. of arsenate of soda in water and mixing the two which the liquid is sent out over the plants in as fine a mist as well together, and adding the whole to 16 gallons of soft water ; possible. Numerous pumps and nozzles are now made by which to this is added a small quantity of coarse treacle. For piercing- this end is attained. Both horse and hand machines are employed, mouthed pests like Aphides no wash is of use unless it contains a the former for hops and large orchards, the latter for bush fruit basis of soft soap. This soft-soap wash kills by contact, and may be and gardens. In America, where trees in parks as well as orchards prepared in the following way:—Dissolve 6 to 8 lb of the best soft and gardens are treated, steam-power is sometimes used. Among soap in boiling soft water, and while still hot (but of course taken off the most important sprayers are the Strawson horse sprayers and the fire) add 1 gallon of paraffin oil and churn well together with a the smaller Eclair and Notus knapsack pumps, carried on the back force-pump ; the whole may then be mixed with 100 gallons of (Fig. 7). The nozzles for “mistifying” the wash most in use are soft water. The oil readily separates from the water, and thus a known as the Yermorei and Riley’s, which can be fitted to any perfect emulsion is not obtained ; this difficulty has been solved length of tubing, so as to reach any height, and can be turned in by Mr Cousin’s paraffin naphthalene wash, which is patented, any direction. The pumps in the machine keep the insecticide hut can be made for private use. It is prepared as follows:— constantly mixed, and at the same time force the wash with great Soft soap, 6 lb dissolved in 1 quart of water; naphthalene, 10 oz. strength through the nozzle, and so to the exterior, as a fine mist; mixed with 1| pint of paraffin ; the whole is mixed together. every part of the plant is thus affected.