18G B.C. Entomological Society 



and, having- no new supply of cut material to enter, for they will not 

 breed in dry logs, enter the living standing trees and kill them within 

 one year. They then spread from year to year throughout the timber 

 stand, leaving devastation in their wake. They also produce conditions 

 favourable to the increase of other insects, usually considered as secon- 

 dary, which, if they do not kill ti-ees outright, nevertheless injure or 

 kill parts of trees and assist the more important species in the general 

 destruction. 



The most important pine killing bark-beetles of British Columbia 

 belong to two species of the genus Dentroctonus, of which one confines 

 its attack to yellow pine, while the other attacks not only yellow pine 

 but white pine and lodgepole pine as well. 



In general, the method of attack is the same for both species. Emerg- 

 ing from a recently killed host tree in June or July, they attack other 

 trees during July and August. Entrance tunnels are cut through the 

 bark to the wood surface, and from the ends of these they excavate 

 tunnels in the inner bark or between the bark and the wood surface, in 

 wliieh they laj' their eggs in small niches cut along the sides. The larvae 

 wliieh hatch from the eggs also cut galleries more or less at right angles 

 to the egg-tunnels and thus generally complete the killing of the tree by 

 girdling it from top to base. Transformation to the pupal stage takes 

 place either in the autumn or during April and May of the following 

 • spring, and the new brood of adult beetles emerges through exit-lioles 

 in the Inirk to attack fresh trees and thus extend the outbreak. 



The number of insects a single tree can harbour is enormous. It 

 has been estimated that in California a sugar pine 9 feet in diameter and 

 200 feet in height has produced one million beetles to spread to surround- 

 ing trees in the forest. Here in B. C. we have caged a yellow pine 24 

 inches in diameter and captured over 6000 of the killing species of beetle, 

 over 16,000 insects of all kinds from the tree, over 10,000 of which were 

 more or less injurious. 



When these beetles emerge from a tree in July and August they 

 immediately attack other trees. The emergence is not all in one day 

 but spread over at least six weeks. By some instinct which they possess 

 they are enabled to concentrate the attack on one particular tree. The 

 first few hundred die by drowning in the pitch, but, as the attack goes 

 on continuously from day to day, the resistance of the tree is weakened 

 and it at last succumbs. If we have a late fall, many of the trees yellow 

 before winter sets in, but, be the fall early or late, nearly all the trees 

 so attacked yellow and die by the last of June of the following year. 

 That is, trees attacked by September are dead the following June. It 

 is therefore necessary in order to control au outbreak that the infested 

 trees be cut and burned before the emergence in July and August. Our 

 working period is from about April 1st to June 15th, as it is almost im- 

 possible to Inirn while tlie snow is on the ground. 



