THE GENUS DENDROCTONUS. 123 



reddish appearance, so that even when the leaves on an infested tree 

 are perfectly normal and there are no pitch tubes the trees thus 

 marked by the birds can be readily located as infested trees. 



As a rule, after the middle of June aU of the broods of this insect 

 have left the trees from which the leaves have fallen, and certainly 

 those in which the twigs have changed from a reddish to a grayish 

 appearance. With few exceptions this may be depended upon, 

 because the parent beetles must have living bark in which to 

 deposit their eggs, so that the freshly hatched larvae will have the 

 proper conditions for their future development. Therefore it is sel- 

 dom that more than one set of broods develops in the same tree. 

 This can happen only when but one side of the trunk or the upper or 

 lower portion is infested and the remainder is not dead when the 

 broods emerge. In this case the remaining living bark will be attacked 

 and yield another set of broods. 



EFFECTS ON COMMEHCIAL VALUE OF THE WOOD. 



The wood of the trees killed by this beetle is not materially reduced 

 in value for several years afterwards, except in so far as the sap wood 

 and heartwood is stained and injured by wood-boring insects, decay, 

 fire, etc. 



FAVORABLE AND UNFAVORABLE CONDITIONS FOR THE BEETLE. 



Favorable conditions for the multiphcation of this insect are found 

 in large areas of virgin forest, where there is a thick stand of old 

 matured timber and where some of the trees have suffered from 

 injury by storms, landshdes, lightning, or other causes. If, under 

 such conditions, the beetle be present in considerable numbers, it 

 may multiply so rapidly that the best timber in the forests over 

 hundreds of square miles may be kUled within two or three years, as 

 has been demonstrated by a number of notable outbreaks in Maine. 

 Unfavorable conditions are found in young, vigorous forests from 

 which the old timber has been removed and utihzed, and especially 

 in forests which are under a modem system of forest management, 

 with regulations either requiring that the matured timber be utihzed 

 or that all injured or dying trees found to be infested with the beetle 

 be felled and barked or floated at the proper time to kill the broods. 



METHODS OF CONTROL. 



Whenever it is positively determined that this species is attacking 

 the hving spruce in a given locahty, or that the bark of hving and 

 dying trees contains hving parent adults or developed broods, some 

 measures should be adopted without delay for its control. 



The removal of the infested bark from the trunks of the trees 

 without burning is all that is necessary to kUl the immature stages of 



