144 THE SCOLYTID BEETLES. 



sometimes goes to the month of September before having finished the operation. It 

 transpires, perhaps, that the mother hibernates and finishes the evacuation of her 

 eggs at the commencement of the following year. 



The larvae eat very close together, growing equally in size and age and making a 

 common cavity underneath the bark. These larvae are white and resemble those of 

 Pissodes or the young larvae of Hylobius. In order to go through the pupal stage, 

 they return to the large space which they left behind them and which is filled with 

 excrement agglutinated by resin. It is there that they construct their pupal cases, 

 unless, departing from their common cavity, they eat out isolated galleries at the end 

 of which the pupal cases are formed. Here they hibernate also and the perfect adults 

 here find. their chamber of hibernation, although they approach a little nearer the 

 place of entrance. 



It is apparent from the preceding that an egg laying extending often over several 

 months produces evolutionary cycles very different from each other as long as it lasts. 



If the larvae which pass over the winter can find a sufficient quantity of heat for 

 their complete evolution they go on to the pupal and adult stages. Others will be 

 found later which will not be able to terminate their larval stage before the weather 

 turns cold again and will be obliged to hibernate in their cells made in the middle of 

 the dried excrement. Between these two extreme cases one finds intermediate 

 stages, possibly, for example, some in the pupal state. 



A hatching taking place toward the middle of this favorable period would not per- 

 mit them, therefore, to attain their growth before winter. 



In winter the adult secretes itself most often in wounds on the tree, where the 

 larval state has been passed, or else it eats out small galleries between the roots and 

 even under the bark, underneath the level of the ground. 



This giant hylesinid lives almost entirely in spruce. The trees on the outskirts of 

 a planting, south and east, so that they are more exposed to the rays of the sun, are 

 the most menaced. As I have already said, the spruces from 25 to 50 years old are the 

 most often attacked, but the old plantings from 60 years and more are not immune. 



Means should be counted among the insects very destructive to spruce. If the 

 first attack does not kill the tree, it does not resist the attacks of the following genera- 

 tion which girdle the trunk by wounds and take all the natural adhesion between the 

 bark and sapwood away. In this case the upper part of the trunk dies rapidly. When 

 attack is made upon the roots the tree continues to live, at least while there are not a 

 great many wounds upon several roots. 



This insect was first introduced in forest entomology by Von Sierstorpf in 1794 under 

 the name of Bostrichus ligniperda, but neither he nor I^atzeburg much later, and who 

 did not repeat the statements made by Saxesen, believed that this insect was a serious 

 enemy. 



Stein, in 1852, did not believe it injurious, but two years later, in 1854, he had to 

 modify his opinion, after great destructions of trees in the forests of Neudorf in Saxony, 

 where micans attacked plantings from 40 to 50 years old, which had to be cut and 

 sold on account of the attacks of insects. 



Before 1858 the insect was almost unknown to Austrian entomologists. At that 

 date Kollar speaks of a serious attack upon the spruces 100 years old in the Imperial 

 Park of Laxenburg near Vienna, where micans had attacked in the beginning only 

 some old trees which resisted for several years. 



At the reunion of the Foresters' Society of Harz in 1867 communications upon the 

 presence of D. micans came in from all sides. They had found it in Harz, in Thurin- 

 gerwald, in Anhalt, and in the plains in the forestry district of Marienthal, near Bruns- 

 wick, without meanwhile considering its presence a great nuisance. 



In 1872 at the same assemblage Gebelers speaks of an attack at Thale in Harz, 

 where D. micans had destroyed 10 hectares of spruces mixed with sylvestral pines, 



"English equivalent, 24.71 acres. 



