THE GENUS DENDROCTONUS. 



61 



in the inner bark. The normal larval mine is first short and thread- 

 like, then suddenly enlarges into a broad cavity, but sometimes, 

 when the bark dies too rapidly or is otherwise unfavorable, a thread- 

 like abnormal larval mine is extended for a much greater distance. 

 When the larvae are fully matured they bore out into the corky outer 

 bark and excavate individual cells (fig. 22) in which those of the 

 summer brood transform to pupae and adults and those of the fall 

 broods pass the winter before going through their transformations 

 the following spring. After the adults are fully matured and when 



Fig. 20.— The south- fig. 21.— The southern pine 

 em pine beetle: beetle. Beginning of egg 



Termination of egg galleries: a, In living bark; 



galleries. (Author's b, in dying bark; c, marked 



illustration.) on surface of wood (white 



area represents normal ap- 

 pearance of wood preserved 

 by resin.) (Author's illustra- 

 tion. ) 



Fig. 22.— The southern pine beetle. 

 Bark showing: a, Pitch tubes; 6, 

 entrance burrow; c, egg gallery; 

 d, ventilating burrow; e, pupal 

 cells; /, exit burrows; g, inner 

 bark; h, outer bark. (Author's 

 illustration.) 



the proper time comes for them to emerge, they bore out through 

 the bark and fly away. 



The flight or swarming of this species evidently occurs late in the 

 evening and at night, and consequently very few observations have 

 been made on the flight habits. The rinding of the beetles in electric- 

 light globes and otherwise attracted to light is conclusive evidence 

 that the beetles fly at night, and the fact that groups of trees are 

 simultaneously attacked by great numbers of the beetles indicates a 

 swarming habit. An especially interesting feature in the congre- 



