800 PROTECTION AGAINST INSECTS. 



Collection of caterpillars. This is undertaken either after 

 November, or by shaking the trees in August. 



This method is less efficacious than smearing girdles of tar 

 on the trees, as at least half the caterpillars escape. 



Collection of pupae. In June and July. 



Collection of the ? moths. This is carried out in July in the 

 morning and on cold wet days before the eggs are laid. 



By this means ichneumons are not destroyed. 



Girdling the trees with grease-bands. This is the best and 

 safest method to adopt when the insects have appeared in 

 large numbers. It was first employed in Silesia in 1829 

 against L. monacha, L., and first in 1866-7 at Gliicksburg, 

 against the present insect. 



The details necessary to ensure success by this measure are 

 carried out as follows : 



The woods which have been attacked are thinned, in order 

 that tar may not be wasted on suppressed stems ; all under- 

 growth which might serve as bridges for the caterpillars is 

 cleared away. 



The coarse bark is removed from the pines in rings 10 to 

 15 cm. broad, in order to present a smooth surface for the 

 tar. Care is taken not to injure the bast. 



The smooth places are covered with a horizontal band of 

 tar or grease 6 to 8 cm. broad in February or the beginning 

 of March, and this operation is repeated at intervals of 6 to 

 8 days, or again in April, when the former application has 

 become too dry to catch the insects. 



Ratzeburg has distinguished experimental tarring from 

 general tarring. The former is used on lines of trees here 

 and there throughout a wood, where a severe attack is feared, 

 and if 5 or 6 caterpillars are caught on each tarred tree, 

 then a general tarring of all the trees is undertaken. There 

 is, however, a danger that the general tarring may come too 

 late, and it is recommended to try the experimental tarring 

 in the autumn, and if a general tarring is shown to be 

 necessary, to take all preliminary measures for it during 

 the winter. The best tar is made from pine roots and 

 stumps ; it should be of a cherry-brown colour and possess 

 a proper consistency, be neither too thick nor too thin, and 



