382 



PROTECTION AGAINST INSECTS. 



always attack in a secondary manner, that is, after a plant 

 has been weakened by previous in jury or disease, nor must the 

 danger arising from them be under-estimated, and this is 

 especially important as regards coniferous forests. 



The most effective means for combating insect attacks 

 consist in careful and cleanly forest management, and in 

 repressing an attack at its very commencement ; once it has 

 attained large dimensions man's efforts against it are almost 

 powerless. In order that his attempts at repression may be 

 successful, the forester must know the life-history and rela- 

 tions to the forest of injurious insects ; for this purpose mere 

 book-learning will not suffice, but must be supplemented by 

 careful and continuous observation in the forest. 



FIG. 194. Ichneumons (/'/////-A' mfiitifrxttiiur}. 3 in flight, ? on tree. 

 From " Cassell's Natural History." 



