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CHAPTKR II. 



GENERAL REMARKS ON INJURIOUS AND BENEFICIAL 



INSECTS. 



L — General Remarks on the Different Methods i;v which Insects Attack and 

 Destroy Tree Growth and the Different Parts of the Tree Affected. 

 — Damage done to (a) Roots; (d) Stems: (i) Young Trees, (2) Poles, (3) Old 

 Stems ; (c) Branches ; (if) Young Twigs ; [e) Buds ; (/) Leaves ; (^^) Inflorescence ; 

 {/i) Fruits and Seeds ; (/) Timber. 



11. — General Remarks on the Methods by which the Insects of Use to the 

 Forester accomplish their Work.— («) Predators, or insects which prey directly 

 upon injurious insects, which they consume at once as food ; {/>) Parasites, or insects 

 which live parasitically upon injurious species, slowly killing them. 



I. — General Remarks on the Different Methods by which Insects 

 Attack and Destroy Tree Growth. 



Specific Account of the kinds of Damage that may be don 



E. 



The tree may be injured or killed in various ways by the insect. The 

 nature of the injury done depends upon two principal things — 



(i) The nature of the aggressor, whether it belongs to the great group 

 of biting insects or to the equally dangerous section which live 

 by suction. 

 (2) The method of growth of the tree and the nature of its parts, 

 whether more or less resistant to insect life or favourable for 

 its sustenance. 



1. The Nature cf the Agg-ressor. 



As we have seen, for our purpose insects may be divided into two 

 groups, the biting insects and the sucking insects. 



It will be obvious that whereas it is a simple matter for an insect 

 provided with a strong pair of biting jaws or mandibles to bore through the 

 old, dead, thick outer bark of a tree to get at the cambium layer beneath, 

 such a procedure would be quite impossible for an insect like an aphis or 

 plant blight, which takes its sustenance through a soft tubular beak and is 

 without strong biting jaws. 



Therefore, the nature of the mouth-parts present in the insect determines 

 to a great extent the part or parts of the tree it is able to attack. 



(a) Biting Insects. — An insect furnished with biting mouth-parts is able 

 to attack every part of the tree from root to fruit or seed. x\s we shall see, 



