FOREST INSECTS 83 



strayed to our coast. In such an event many trees are laid 

 flat over extensive areas. A common large longicorn beetle 

 (Monohammus) which is widely distributed in this region 

 finds these trees excellent material, and its work soon be- 

 comes apparent. The beetles deposit their eggs in little pits 

 which they excavate in the bark, and their large succulent 

 larvae tunnel the wood with their food burrows until it is unfit 

 for most purposes. Outbreaks of this kind can, of course, be 

 foreseen much more readily than some of the other type 

 which we have referred to previously, but the damage they 

 cause is no less severe and the application of remedial meas- 

 ures is frequently very difficult. 



The distinction between those insects that affect the wood 

 or bark of living trees and those occurring in ones recently 

 dead is not to be closely drawn, and when much dead or dying 

 timber is present in a forest, it may furnish such favorable 

 opportunities for the development of some species, that the 

 whole forest becomes endangered; for when thus produced in 

 large numbers, many wood-boring or bark-beetles that live 

 normally in dead wood, may migrate to living trees and injure 

 or destroy them. Such dead or decaying timber in a forest is 

 thus a menace to the living tree population through the part 

 which it takes in the multiplication of these forms that may 

 on occasion affect living trees. Fire-scorched trees may in 

 the same way be attacked by bark-beetles and succumb 

 where uninjured trees would not have suffered, and vice versa, 

 insect-killed trees, especially in the case of pure coniferous 

 forests, may constitute a great fire menace due to the more 

 combustible nature of the lifeless trees after the bark-beetles 

 or other primary enemies have left them. There appears to 

 be good evidence that some of the destructive forest fires 

 which have occurred in the great coniferous forests of the 

 western United States have been furthered by insects in this 

 way. 



An especially interesting example of a series of insect 

 enemies that may follow one another in a tree as it passes 

 from robust health into a gradual decline that ends in death, 



