74 SOME INSECTS INJURIOUS TO FORESTS. 



Those of some species develop to the adult stage within the inner bark 

 and are exposed when the bark is removed, while those of other 

 species transform to the adults in the outer corky bark and the larvae 

 are not exposed when the bark is removed. Some species have two 

 or more generations in a season or annually, while others have but 

 one, and in a few species it requires two years for a single generation 

 to develop. (Hopkins, 1909&.) 



The barkbeetles of the genus Dendroctonus represent the most 

 destructive enemies of the principal coniferous tree species of Ameri- 

 can forests, and at the same time are among the easiest of control. 

 The general requisites for success are embodied in the following rules : 



(a) Give prompt attention to the first evidence of a destructive 

 outbreak, as indicated by an abnormal percentage of yellow or red 

 topped dying trees, and especially when such trees occur in groups of 

 ten or more or cover large areas; (&) secure authentic determination 

 of the particular species of insect responsible for the trouble; and 

 {c) take prompt action toward its control according to specific expert 

 advice, published or otherwise, on the best method for the destruction 

 of the necessary 75 per cent or more of the insects in the infested trees. 



Some of the methods to be adopted to meet the requirements of 

 various local conditions are as follows : 



(1) Utilize the infested timber and burn the slabs during the 

 period in which the broods of the destructive beetles are in the imma- 

 ture stages or before the developed broods emerge from the bark; or 



(2) Fell the infested trees and remove the bark from the main 

 trunk and burn the bark if necessary ; « or 



(3) Remove the infested bark from the standing timber and burn 

 the bark when necessary ; ^ or 



(4) Immerse the unbarked logs in ponds, lakes, or streams, where 

 the bark will remain soaked long enough to kill the insects; or 



(5) Remove the unbarked logs or products to a locality where 

 there are no trees liable to attack within a radius of 20 miles or more. 



Maintaining Control of Barkbeetles. 



Future trouble of a serious nature from barkbeetles which kill trees 

 can be prevented Avithin a given forest or area of greater or less extent 

 if an insect-control policy is adopted in connection with, or independ- 

 ent of, a fire-control policy by which groups of dying trees will 

 receive similar prompt attention as that required for the prevention 

 or control of forest fires. 



1)1 state and national forests. — In all forest reserves in which there 

 is an organized force of rangers and fire wardens or patrols each 



o If tbe broods devcloii to adults in the outer l)ark, it must be burned ; if tbey 

 develop in tbo inner bark and are exposed when tbe bark is removed, burning is 

 not necessary. As a rule the burning of tbe tops to destroy tbe insects is not 

 necessary. 



