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 larvae. 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. 



