298 



PROTECTION AGAINST INSECTS. 



first year and become successively smaller and weaker, rapidly 

 ensue. At the same time, insect-parasites and bacterial 



diseases become 

 more and more 

 active, until the 

 caterpillars die 

 from these causes 

 in immense num- 

 bers. 



This pest is most 

 dangerous in pure 

 Scots pine forests, 

 . on sandy soils, in 

 dry districts, and 

 in the plains and 

 hills of North and 

 North-eastern Ger- 

 many, less so in 

 the south and west; 

 it is rare in moun- 

 tainous districts. 



A succession of 

 warm summers 

 favours its multi- 

 plication to an ex- 

 traordinary degree. 

 In the ten years, 

 1863—72, in the 

 forests from West 

 . Prussia to Saxonj'', 

 442,500 acres of 

 Scots pine forests 

 were attacked, and 

 70,000,000 cubic 

 feet of timber 

 killed. In 1888-9, 

 the valleys of the llhine and Maine, in Hesse, were ravaged, 

 and the caterpillars devoured the needles even of 10-year-old 

 pines. 



Fig. 149. — Ro.sette-needlcs {a) on Scots pine, I'ollowin^j 

 defoliation by G. piiii, Oclish. [Xalitral nizc) 



