FOREST PROTECTION 83 



Really effective means of prevention are wanting, though 

 in this case, again, rings of patent tar round the stems are of 

 much assistance. They prevent larvaej hatched from eggs 

 laid low down on the stems, from reaching the crowns ; and 

 they are even more useful in another way the caterpillars 

 while young let themselves down from the tree-tops by long 

 spun threads, but to re-ascend they require to crawl up the 

 stem. The sticky band, however, intercepts their progress, 

 and they die in thousands below it. On the Continent this 

 measure has frequently been carried out on an extensive scale, 

 and has saved many forests. The pest invariably spreads 

 from quite small centres of infection, so that every effort 

 should be made to check an attack in its first stages. If then 

 neglected, it is impossible to prevent a calamity. 

 , OAK-LEAF ROLLER MOTH, Tortrix viridana (Fig. 16). The 



f 



FIG. 16. OAK-LEAF ROLLER MOTH ( Tortrix viridana) 

 a. Moth. b. Larva. c. Pupa. 



caterpillars, which are of a dirty green colour and about half 

 an inch in length, appear in spring from eggs laid in the 



