due to settlers girdling trees and leaving cut trees, or 

 portions of them, on the ground through one breeding season. 

 Similarly, railroads in clearing rights -of -way, trail and 

 road builders, power companies in clear ing for reservoirs, 

 lumbering operations, and various other activities, leave on 

 the ground fresh material in which injurious insects breed. 

 IToraal infestation ie always present, consequently epidemics 

 follow. Probably, the most common cause of epidemic insect 

 infestations is lumbering operations. Stumps, cull logs, 

 tops, limbs, and brush left on the ground longer than the 

 life cycle of the cownon bark borers often start an epidemic. 

 The only cases where this refuse does not breed the various 

 injurious Lark "borers in large or small quantities are those 

 in which the material dries sufficiently before the broods 

 are flying to prevent their infesting it or where it is in 

 dense shade as sometimes occurs on north hillsides and deep 

 canons. 



Stumps:- Stumps breed the Red Turpentine Beetle (Dendrocton - 

 us valens) and many secondary beetles injuring sap and heart - 

 wood, especially flat and rotmdhead borers. 



Cull Logs:- Cull logs almost invariably breed the tree-kill! 

 beetles unless the bark is burned off or otherwise removed . 

 This is especially so in yellow and siigar pine where Pendroc- 



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