OBSERVATIONS ON THE ENTOMOLOGY OF THE SCOTS PINE. II9 



In or on the stem the following occur : — 

 (a) Breeding — H. palliatus. 

 M. pintperda, 

 P. pini. 

 {b) Feeding — H. palliatus. 



H. abietis (young pines only). 

 On the stump and roots occur : — 

 {a) Breeding — H. abietis. 



H. ater. 

 {b) Feeding — H. palliatus. 



H. ater (on young pines only). 

 It is seldom that all these species are found on any one pine, 

 or even in any one pine wood. In some woods only one species 

 may be present, or all but one. In the normal, or rather the 

 average, Scots pine wood, the majority of the species occur, but 

 on different trees and in different localities at any given period. 

 This may be due to several causes, the chief of which, however, 

 is the fact that each species or group of species attacks the pine 

 under particular conditions, and only under these conditions. 

 It is generally known that only rarely do the bark beetles and 

 the weevils attack trees in full health. As a rule our pine 

 beetles prefer sickly trees. They do not, however, prefer the 

 same reduction of vitality ; one species will attack on the first 

 signs of weakening vitality, another will follow on the heels of 

 this species when the vitality has been further reduced, while 

 others will delay even longer. Thus Myelophilus pintperda is 

 usually the first to attack. It is followed by H. palliatus and 

 Pissodes. All these attack the stem. On the stump and roots 

 Hylobius is first to attack, then H. ater follows it. In a sickly 

 standing tree, the following is the sequence I have observed 

 most frequently : — 



1. The stem is attacked by M. piniperda. 



2. The stem is attacked by H. palliatus^ and the stump and 



roots by Hylobius. 



3. Myelophilus has gone from the stem, H. palliatus and 



Pissodes pini remaining. Hylobius remains on the 



roots accompanied by H. ater. Pityogenes bidentatus 

 is appearing on the twigs. 



4. The stem is quite deserted. On the roots Hylobius is 



rare, while H. ater is increasing. P. bidentatus is 



