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 seg- 

 mented 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 (Cheiving). — 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 insert- 



ing their tubular mouth parts into the sap cells of pkmts 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 Iioav 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 num- 

 ber 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 



