15 



The eggs are deposited singly in shallow niches cut by the female along the 

 sides of the egg-tunnel at intervals of a half-inch or more ; and the young larvae, 

 or grubs, which hatch in about eight days, bore irregularly, mainly in the outer 

 layers of the inner bark. When nearly full-grown the grubs bore outwards 

 deep into the middle layers of bark, enlarge the ends of the tunnels to form 

 " pupal-cells," and there transform to the resting-stage or pupa. The adult 

 beetles, which appear later from the pupae, bore round holes through the outer 

 bark and escape to spread the infestation to green trees, or to increase the 

 numbers in the trees already infested. 



Fig. 4. Larva or grub of the Western White Pine Bark- 

 beetle. Greatly enlarged. (Original). 



Many of the beetles attack the trees near the red-tops from which they 

 escape: but swarms, spreading from the old infestations, attack isolated trees 

 and small clumps of trees at a considerable distance. The outbreak thus spreads 

 by the increase in the number of the clumps and scattered infested trees, as well 

 as by the enlargement of the individual clumps. 



THE SEASONAL HISTORY OF THE BROODS. There are, at least about Prince- 

 ton, one brood and a partial second one each season. During the winter there 

 may be found in the bark: the parent adults of the fall brood; young, light- 

 coloured adults still in the pupal-cells; and many larvae, or grubs in various 

 stages. 



The over-wintered parent adults extend their tunnels, or start new ones, 

 when the weather becomes warm in spring, and deposit eggs. The adults 

 developed from these eggs appear, apparently, early in August and start tunnels 

 in the trees already attacked by the broods of over-wintered young adults. At 

 Princeton this year these over-wintered parent adults largely left the bark and 

 started new tunnels. 



The over-wintered young adults emerge from the red-tops during July and 

 attack green timber about the old red-tops or spread to isolated trees or clumps. 

 About Princeton this season they apparently appeared largely during the first 

 half of the month. By the middle of August the bark of the trees attacked by 

 them was filled with their larvae, of all sizes up to nearly full-grown; and the 

 foliage, while not yellow, appeared slightly faded, so that such trees could 

 usually be picked out as unthrifty. They could usually be distinguished by 

 the gum-tubes which studded the bark by hundreds. It often happens that 

 most of the gum-tubes are high up in the trees and are difficult to distinguish 

 from below. This fact should be remembered when marking infested trees for 

 cutting. The larvae of this brood pupated and had in most cases left the bark 

 as adults before the end of September. These adults apparently started fresh 

 tunnels in the same trees, and deposited eggs, the larvae from which are to be 

 found in the bark during winter. 



