Page:A primer of forestry, with illustrations of the principal forest trees of Western Australia.djvu/110

104 CHAPTER XIV.

INSECTS AND FORESTRY.

Economic Forestry Entomology is that phase of Entomology which relates to the study of insects living in the Forests, and the encouragement of the friendly insects and the artificial control of injurious species.

Insects.

The word "Insect" is derived from the Latin Insecare, to cut or notch, and is expressive of the characteristic parts or segments of which the body of an insect is built up. Correctly speaking, the term is applied to those air breathing segmented animals which, in the adult stage, have six legs and the body deeply incised twice, so that it is divided into three parts or regions, namely, the head, thorax and abdomen. A true insect is therefore known as a Hexapode, Hex six, and pous a foot.

Space will not permit of a description of the various organs which lie hidden within the horny bodied creatures we call insects, but mention must be made of the types of mouths possessed by them. It is very essential that we shall be able to determine the method of the feeding of an insect. The mouth parts are, in general, of two types, namely, chewing and sucking:—


 * 1. Mandibulata (Chewing).—Those plant or insect feeding insects which chew or cut off their food, such as caterpillars, grubs, beetles, etc. Amongst this group are many beneficial insects, which feed upon other insects and are known as predaceous parasites. Examples—the larval and adult stages of Ladybird, Ground and Tiger Beetles, etc.


 * 2. Haustellata (Sucking).—Those insects which obtain their food by inserting their tubular mouth parts into the sap cells of plats and suck out the juices. Examples—Aphides, Scales, Bugs, etc. Amongst this group there are also many beneficial parasites which suck out the body juices of their victims. Examples—Predaceous Bugs, Syrphus Flies, Lace Wing Flies, etc.

It is essential to have a knowledge of how an insect feeds before we can suggest a treatment. Biting or chewing insects are destroyed by the application of poison to their food which is taken into the stomach and thus causes poisoning and death. For this purpose, Arsenate of Lead, Paris Green and other poisons are applied to the food of the Mandibulata insects. For the Suctorial, these poisons so applied would be useless, as the sucking, insects would simply push their sucking beak through the coating of poison on the leaf and imbibe the healthy sap, and be not in the least affected by the presence of poison on the foliage or bark. To destroy sap sucking insects we must, therefore, apply some wash or spray that will either by its caustic action destroy by contact with insects, or we must force by means of a pump, the liquid poison through the breathing spiracles of the insect. It is, therefore, obvious that it is essential to have at least a knowledge of how insects feed so that the right treatment may be applied. Resin and Soda Wash, Kerosene Emulsion, Whale Oil, Soap, etc., are contact washes. Tobacco Wash, Quassia Chips, etc., are contact poisons. Arsenate of Lead, Paris Green, etc., are internal poisons.

The Breathing Spiracles.—The breathing of insects is quite dissimilar to ours, for the air enters the body through a number of small openings, varying in number and spoken of as spiracles, a couple of which are found on most segments of the abdomen and upon the thorax. These may be observed on the sides of the abdomen of any adult insect as small spots or holes, and similarly on the sides of the bodies of grubs and caterpillars, and on the posterior segment of maggots. The