412 FOREST ENTOMOLOGY. 



shade-bearers — beech and other trees — and growth will be very much 

 stimulated. It has been proved by the AVoburn 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 do very badly, 

 partially owing to insect-damage, and are often considered too good to 

 destroy. This class of trees, after being planted for a few years, 

 could be cut down to the ground, and then they would come away 

 as strong young 'trees, provided they are well sheltered with the 

 remainder of the crop, or under the protection of netting, and re- 

 ceiving 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 Avould 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 sjjecial 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. I^ow 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 



