392 FOREST ENTOMOLOGY. 



stimulated. It has been proved by the Woburn and other experi- 

 ments that grass has no place in an orchard ; and as the case of young 

 woods is practically analogous, it would be well for the health of 

 young woods if the grass could be got rid of as soon as possible by the 

 density of the young thick crops. 



In the nursery-lines many species of hardwood trees which may be 

 doing badly, partially owing to insects, after being planted for a few 

 years could be cut down to the ground, and then come away as strong 

 young trees, provided they are well sheltered with the remainder of 

 the crop, or under the protection of netting, and receiving attention 

 for the first year. 



In dealing with Insecticides, or the destruction of certain insects by 

 the application of special chemicals and mixtures in varying degrees 

 of strength, or otherwise by the application of special mixtures as sold 

 by respectable firms or individuals, it will be obvious that in a work 

 of this class it would be very improper either to support or condemn 

 any " mixture " in the market. It is therefore considered advisable 

 to simply give a few general principles. 



In the first place, it should be remembered that the use of any in- 

 secticide should be, as far as possible, applied intelligently (1) as 

 regards the life-history of the insect ; (2) what is to be the actual or 

 prospective effect on that particular stage of the insect under the an- 

 ticipated remedy ; and (3) how far such remedies may be practicable. 



It is important to bear in mind the structural and physiological 

 functions of an insect (1) as regards the structure of the mouth and 

 method of feeding ; (2) the method of respiration or breathing ; and 

 (3) in some special cases the method of reproduction. The applica- 

 tion of effectual insecticides must be through one or other of these 

 mediums. 



As regards the poisoning of the insect through feeding, it must be 

 borne in mind that there are three distinct methods of feeding viz., 

 biting, piercing, and sucking. The piercing and sucking forms, how- 

 ever, are not always easily separated. JNTow take a typical case of 

 general insecticide application viz., spraying, and consider obvious 

 results. The biting form of mouth, as seen in the beetle, would take 

 the liquid along with the full structure of the leaf ; or if the insect 

 only ate the upper surface of the leaf, leaving the veins and under 

 surface, it would obviously take more liquid in proportion than the 

 other insects. But if the insect were literally of the piercing type, 



