302 ■ PROTECTION AGAINST INSECTS. 



hibernating caterpillars were collected at a cost of 20s. per 

 10,000. The value of the annual increment of Avood saved 

 was 8s. per acre, as against 7s., the cost of the tar rings. 



The efficacy of the tar ring is less interfered with by frost 

 than by great heat, as the latter easily melts it and causes it 

 to run down the tree. Most of the caterpillars which attempt 

 to cross the rings adhere to the lower .part of them ; but about 

 3 per cent, of them, chiefly the larger ones, manage to cross 

 the rings, although of these about 59 per cent; soon die from 

 the effects of the tar, so that only 1-2 per cent, of the whole 

 number really survive and pass the rings. 



The caterpillars whose way to the tree-crowns is thus cut 

 off, return to the ground and try to find their way to other 

 trees ; they are therefore prevented from so doing, by isolating, 

 by means of trenches, the wood containing the tarred trees 

 from other woods which have not been so protected. 



Caterpillars infested by ichneumons, or fungoid diseases, 

 may be introduced amongst those which are healthy. 



In cases where the attack is very bad, but localised over 

 a small wood only, the soil-covering is burned whilst the 

 caterpillars are hibernating, or even the whole wood is burned, 

 measures being taken in both cases to protect the adjoining 

 woods from the spread of the fire. 



Robert Hartig, in 1871, experimented near Eberswald on 

 the effects of the (fifferent methods of protecting the Scots 

 pine from these caterpillars, with the following results : — 



The collection of hibernating caterpillars, as long as the 

 moss and dead-leaf covering is replaced in position, has no 

 bad influence on the growth of the tree. 



The jarring of young trees in order to knock oft' the cater- 

 pillars involves local decay in the bast, and consequent 

 reduction of increment. 



Tarring does not hurt the trees in the slightest degree. 



2. Bomhjx neustria, L. (Laclcey-Moth). 

 a. iJesrri/tlioii. 

 Moth with spread of wings of 30 to 40 mm. Body and fore- 

 wings ochreous-yellow or red-brown, the latter traversed across 



