62 



THE SCOLYTID BEETLES. 



gating habit of the beetles was observed by Mr. W. F. Fiske, who 

 found great numbers congregated under the loose flakes of bark of 

 healthy trees just before their simultaneous entrance into the living 

 inner bark. Another peculiar habit of the beetles is that of migrat- 

 ing from one locality or group of trees where the broods developed 

 to another locality or group of trees some distance away, instead of 

 continuing their attack on the trees immediately surrounding those 



Fig. 23.— The southern pine beetle: Old egg 

 galleries in living tree, with surrounding 

 callus of new wood. (Author's illustration.) 



Fig. 24.— The southern pine beetle. 

 Egg gallery in living tree marked 

 on surface of wood six years before 

 block was cut from tree: a, Mark 

 of gallery on original surface; 6, 

 resinous wood; c, surface scar six 

 years later; d, original surface or 

 7-year-old annual layer of wood; e, 

 six subsequent annual layers of 

 wood formed over original wound. 

 (Author's illustration.) 



from which they emerge. Apparently 

 there are rare exceptions to this rule. 



While this species will breed in injured 

 and felled trees, it shows a decided prefer- 

 ence for those living and healthy, whenever 

 it occurs in sufficient numbers to attack and kill them. Its broods 

 of larvae must have living, or at least partially living, bark in which 

 to complete their rapid normal development. It attacks the bark on 

 the middle or upper trunk of medium to large pine and spruce trees, 

 and usually selects the largest and best trees first. After the larger 

 trees are killed the middle to lower trunk of the smaller trees may 

 be attacked. The habit of attack and methods of excavating gal- 

 leries are similar to those of the smaller western and Mexican spe- 



