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 
ji 
Fig. 20.— The south- 
ern pine beetle : 
Termination of egg 
galleries. (Author's 
illustration.) 
jfclyjS 1 ill? 
Fig. 21.— The southern pine 
beetle. Beginning of egg 
galleries: a, In living bark; 
6, in dying bark; c, marked 
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; b, 
entrance burrow; c, egg gallery; 
d, ventilating burrow; e, pupal 
cells; /, exit burrows; g, inner 
bark; /;, 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 finding 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- 
