5 i2 FAMILY SCOLYTIDAE 



free 3. Fully grown larvae, pupae, immature and fully mature beetles. 

 These latter were leaving the tree, and were attacking a perfectly green 

 tree in the neighbourhood. 



Tree 4. -Fully mature male and female beetles, eggs, and young larvae, 

 the tunnels of the latter, giving off at the lower portion of the egg-gallery, 

 being already as much as half an inch long. 



The above material furnishes us with the life history of this pest 

 from the time that it began its operations after the period of hiber- 

 nation to the middle of June. The insect passes the winter as a 

 beetle or grub ; in the case of such a thin-barked tree as the chilgoza 

 it would certainly be killed off in the pupal stage by the frost, and this 

 probably happens to that portion of the generation which has reached 

 the pupal stage when the winter sets in. If it hibernates as a beetle 

 it issues from the tree as soon as the warmth of spring makes itself 

 felt, and bores into fresh trees to lay the eggs of the first generation 

 of the year. Should the insect pass the winter in the grub stage, the 

 larvae will pupate with the first warmth and issue shortly afterwards 

 as beetles. In the latter event it will be seen that the individuals who 

 passed the winter in the mature state will have a start over those who 

 were in the larval one, and this accounts for the apparent overlapping of 

 generations which may be noticed in the case of this and other bark-boring 

 beetles such as Scolytus, Tomicus, and other Polygraphi. By overlapping 

 of generations I mean that in one and the same tree may be found egg- 

 galleries with the offshoot larval galleries well advanced, and therefore a 

 week or two old, whilst others are only just commenced by the mother 

 beetles, they being a week or two behind the first insects to enter 

 the tree. 



In the first tree mentioned above, mature larvae, pupae, and immature 

 beetles were found. These had all developed from eggs laid some time early 

 in May of the year 1905. The attack commences by a male beetle 

 boring into the tree through the bark until it reaches the sapwood. In 

 this it eats out a depression which is the pairing-chamber. It is joined 

 here by a female beetle who enters by the same hole. After pairing 

 with the male the female commences to eat out a longitudinal gallery, 

 which is always more or less parallel to the long axis of the tree. This 

 gallery is slightly broader than the width of the beetle. On either side of 

 it she eats out little recesses and places one egg in each. These recesses 

 are made on both sides of the gallery, but are usually more numerous on 

 the one side than on the other, and are closer and more evenly distributed 

 in the lower portion than towards the apex. See fig. 308 : (a) pairing- 

 chamber ; (b) egg-gallery; (c) recess in which egg is placed. In fact, as the 

 e gg-g a ll erv becomes longer, the beetle's egg-laying powers appear to become 

 eaker and more erratic. In the roof of this gallery, i.e. in the bark, 

 she bores small circular offshoot galleries, which pierce through the bark 



