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 all 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 COMMERCIAL 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 sapwood 
and heartwood is stained and injured by wood-boring insects, decay, 
iire, etc. 
FAVORABLE AND UNFAVORABLE CONDITIONS FOR THE BEETLE. 
Favorable conditions for the multiplication 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 sufTered from 
injury by storms, landslides, 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 killed 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 utilized, and especially 
in forests which are under a modern system of forest management, 
with regulations either requiring that the matured timber be utilized 
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 living spruce in a given locality, or that the bark of living and 
dying trees contains living 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 kill the immature stages of 
