52 College of KForestry. 
gallery are placed at a distance of 2 mm. or more apart, 
while in the latter part of the gallery they are crowded so 
closely that the egg niches are not entirely separate, often 
being as many as three to each millimeter. This is espe- 
cially noticeable in egg galleries which are longer than 
usual. It would seem that at the beginning the physical 
strength of the female was greater than her egg-laying 
power and this strength is used up in placing the eggs an 
unusual distance apart. Later her strength is exhausted 
before the supply of eggs is and she places the eggs so 
closely together that many of the larvae arising from them 
do not survive, as may be seen by a study of the larval 
burrows. 
The larval burrows have already been described in con- 
nection with the account of the larvae. They vary greatly 
in length from 18 mm. or less to over 40 mm., the average 
length of twenty being 31 mm. The course of the larval 
burrows is in general at right angles to the egg gallery, 
_ but when arising from galleries which are not transverse 
the larvae tend to burrow longitudinally with the fibres of 
the bark and wood (Fig, 26, 27). Larval burrows from 
ege galleries which parallel each other closely show a very 
tortuous course often crossing and recrossing each other 
many times (Fig. 28), and the engravings clearly show 
that a large percentage of the larvae do not succeed in 
completing their life history. The early part of the larval 
burrow is entirely in the bark but upon the surface of the 
sapwood, so when the bark is removed later the early 
burrows show the white of the sapwood while the space 
between them appears brown, due to the dried cambian 
(Fig. 28). The later larval burrow grooves the sapwood 
deeper and deeper and finally the pupation chamber usually 
lies with from one-half to all of its depth in the sapwood 
(Fig. 27). 
If any large proportion of the brood succeeds in reaching 
adult condition, much of the engraving is sure to be ruined 
by their feeding burrows. This is especially true when 
the brood reaches the beetle stage a few weeks before the 
