50 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
of 80° F., or higher, all the bark beetles on the top half of the logs 
will have been killed. Then the men return and with peavies turn 
the logs completely over, so that the other side will be exposed. Craig- 
head (779) reported that this method had been tested on the southern 
pine beetle and on several species of Jps with good results. 
Penetrating Oils 
Recent experiments have demonstrated that certain chemicals, 
when dissolved in oils and sprayed on the surface of the bark will 
penetrate the bark and kill the bark beetle broods beneath. The most 
effective formula tested to date is 1 part of orthodichlorobenzene to 
4 to 6 parts of kerosene or light fuel oil. This solution when apphed to 
infested pine bark at the rate of about 4 ounces per square foot will 
give effective control. Oluls of this type, however, are effective only 
when temperatures are above 60° F. during the day and are easier to 
use when the bark is dry. This method of control has possibilities 
in treating infested trees during the summer months, when the fire 
hazard is too great to permit burning. It is best adapted to thin- 
barked trees, where the bark is of such a texture as to absorb the oil 
readily. It has not been tried for the control of the hickory bark 
beetle, but has proved effective against the southern pine beetle and 
elm bark beetles. This treatment does not save the tree. 
The Peeling Method 
The peeling method of control can be used against the immature 
stages of bark beetles that develop between the ‘bark and the wood. 
When the bark is removed they die of exposure or are destroyed by 
ants, birds, and voles and other mammals. The method is especially 
applicable to moderately thick-barked trees that are easily peeled. 
It has been used extensively for the control of several western bark 
beetles and the spruce bark beetle in the Northeast. It is a relatively 
cheap method if the trees are treated after the bark has been loosened 
by the insects, and it does not involve any fire risk. Furthermore, no 
specialized technique is necessary and ordinary woodsmen can do the 
work very effectively. Occasionally when the infestation is massed 
at the base of the tree, as it often is with the spruce bark beetle, long- 
handled bark spuds can be used and the felling of the tree avoided. 
The Trap-Tree Method 
The control of bark beetles by trapping them in logs felled for 
that particular purpose has been recommended repeatedly in European 
literature, but extensive tests in this country have proved this method 
of control to be of little value for our insects and for conditions en- 
countered here. The method can be used in special cases. Often, 
however, trap logs attract great numbers of beetles from the sur- 
rounding areas and cause them to attack the green standing timber 
nearby rather than the trap logs. 
For further details on the use of these methods consult Keen (262) ; 
for the eastern spruce beetle, see Swain (402) ; for the southern pine 
beetle, see St. George and Beal (377) ; and for the hickory bark beetle, 
see Hopkins (235). 
