THE GENUS DENDROCTONUS. 31 
bark and thus destroy the broods; (e) by transporting the infested 
trunks a sufficient distance (20 to 50 miles or more away) from the 
forest and away from any living spruce or pine, so that the beetles 
emerging from them will find no trees to attack. 
ATTEMPTS AT COMPLETE EXTERMINATION OF THE BEETLES UNNECES- 
SARY. 
As a rule, it is not only useless but unnecessary to attempt the 
complete extermination of one or more species of the beetles within a 
given forest. It is necessary, however, to so reduce and weaken their 
forces that they can not continue an aggressive attack, thus leaving 
them to depend upon weakened and felled trees for their support 
and to occupy a defensive position against their natural enemies. 
It must be kept in mind that the beetles must occur in great num- 
bers in order to be successful in their attack on healthy trees. If 
their number is reduced and kept below that required for killing 
trees they can do no harm. Therefore in the case of a destructive 
outbreak it is necessary to destroy only from 50 to 75 per cent of 
the beetles in order to bring them under complete control. 
REQUISITES FOR SUCCESSFUL CONTROL. 
The principal requisites for success in dealing with these beetles 
are: (a) Prompt recognition of evidences of their presence before 
they have extended their depredations beyond a few scattering 
clumps or patches of trees; (b) positive identification of the species 
involved; (c) prompt action in adopting the proper method of con- 
trol; and (d) reliance on expert advice relating to the essential features 
in the habits and seasonal history of the insects, on which the action 
is based. 
HOW TO CHECK AND CONTROL AN EXTENSIVE INVASION. 
If the depredations by species 9, 10, 13, 14, or 15 have spread over 
a large area and there is yet a large amount of living timber or adja- 
cent healthy forests to be protected, a careful survey should be made 
in September, October, or November, for the purpose of locating the 
areas and localities of new infestation in which the trees were attacked 
during the summer and fall and which, at the time of survey, 
contain living broods. The areas of principal infestation and the 
larger patches of infested trees should be designated on a map, and 
estimates made of the total amount or percentage of timber affected. 
This will form a basis for definite plans and the organization and 
equipment of a sufficient force to do the required work within the 
specified time designated for each species. Then, if regular logging 
