INSECTS 131 



Looking further ahead, there is another point 

 which deserves mention. It is a well-known fact 

 that with the increase of areas of a pure crop of 

 any kind, agricultijral or forestal, takes place a like 

 increase in the pests which feed upon it. This 

 especially applies to forest pests, an^ to none more 

 than the bark beetles, who deposit their eggs in the 

 sappy layer beneath the outer bark. Pick up a 

 bit of old bark in the woods. On its inner surface 

 you will see patterns and designs as if scored out 

 with a sharp instrument. You may see identical 

 patterns on the outer surface of the stem from 

 which the piece of bark has fallen. These are made 

 by bark beetles and their grubs. If sufficiently 

 numerous, the whole of the inner bark of the tree 

 may be covered with these designs, and the green 

 tree will have been killed by the hundreds qi thou- 

 sands of these small creatures who hved in it. 



In crops of one species reproduced over con- 

 siderable areas of country, you provide a large 

 amount of food in compact blocks, thus favouring 

 the increase of a pest addicted to feeding on 

 this particular species. The fact that there 

 have been no serious records of plagues of bark 

 beetle and other pests on a large scale in Britain in 

 the past, such as, e.g. ^ the forests of France, Germany, 

 and America have witnessed, by no means infers 

 that we shall not have to face them in the future. 



There is one forest insect which many are 

 acquainted with — the little caterpillar which 

 appears in its hosts and strips the oaks of their 

 leaves in early summer. These attacks do not 



