40 THE SCOLYTID BEETLES. 
in which the conditions are not so favorable for normal develop- 
ment. There are also broods from eggs deposited by overwintered 
parent adults, so that the period of development and emergence of 
all of the overwintered broods is prolonged and irregular. In fact, 
some of the overwintered individuals of certain species may not com- 
plete their development and emerge until the second season of ac- 
tivity. These retarded broods are not of much economic importance, 
but they introduce an element of confusion in defining the limits of a 
given generation. On the other hand, periods of normal or principal 
development, transformation, and emergence of the broods are of 
especial economic importance, since a knowledge of them is quite 
essential for successful control. 
Seasonal history. — According to the writer's interpretation, the 
seasonal history of an insect is the history of the broods of the species 
from the beginning of activity in the spring of one year to the end 
of the hibernating or overwintering period in the spring of the next 
year. 
Life history. — The term "life history," as frequently employed, is 
synonymous with seasonal history, but to be more exact it is the 
history of an individual from the egg to maturity and death, includ- 
ing its natural enemies, environment, or any other phenomena 
affecting its life. 
Egg gallery (fig. 7, etc.). — The egg gallery is the burrow made by 
the adult beetles, along the sides of which the eggs are deposited. 
Larval mines and pupal cells (figs. 19, 22, etc.). — The larval mines 
are the food burrows made by the larva?. The pupal cells are cavi- 
ties excavated by the larvae at the end of the larval mines, in which 
to transform to the pupae and adults. 
Food burrow. — A food burrow is one excavated into the living 
bark by the adult beetles for the purpose of obtaining food. 
Entrance burrow (figs. 79, 99). — The entrance burrows are the 
holes made by the parent beetles through the outer and inner bark 
preliminary to excavating the egg galleries. 
Ventilating burrows (figs. 79, 99). — Ventilating burrows are the 
vertical burrows located at frequent intervals in the roof of the egg 
gallery and extending outward to or near the surface. They are 
utilized by the parent adults as a place in which to turn around, or 
in which to pack the boring dust, or through which to eject the dust, 
as the case may be. 
Exit burrows or exit holes (figs. 8, 22). — The exit burrows or exit 
holes are the clear-cut holes in the outer bark through which the 
adults of the new broods emerge from the tree. 
Boring dust (figs. 79, 99, etc.). — The sawdustlike borings ejected 
from the egg galleries or packed in them and in the larval mines is 
referred to as boring dust. 
