DOUGLAS FIE PITCH MOTH. 7 



LOCATION OF AFFECTED AREAS. 



The Douglas fir pitch moth has apparently a very marked habit 

 concerning the preferred areas in given localities. An area in which 

 it is depreciating the timber now may be readily located by simply 

 watching the logs at the mill as they go through the saw and ascer- 

 taining where those with pitch seams come from. It may seem a 

 matter of speculation to undertake to determine localities where the 

 insect is numerous at present by thus examining trees which have 

 been infested a century or more in the past, but it has been ascer- 

 tained to be an absolutely reliable method. The success of this test 

 not only proves that the sesiid is the cause of the depreciation, but 

 it shows us in addition how we may determine the exact localities 

 where the merchantable timber is liable to serious damage by the 

 insect, because wherever the injury exists in the young, growing 

 timber, which will be "loggable" a hundred years from now, it is 

 practically certain that the mature trees had been afflicted in the same 

 manner in their youth. 



RANGE OF THE INSECT. 



As already indicated, the range of this insect is over the northern 

 Rocky Mountain and Pacific Coast regions and extends in all proba- 

 bility through the entire native range of the Douglas fir. From my 

 own observations and numerous field notes and from larva? collected 

 in various parts between the northern boundary of the United 

 States and latitude 41° 30' K and from the eastern boundary of the 

 State of Montana to the western coast by- other members of the 

 Branch of Forest Insects and kindly put at the disposal of the writer, 

 it is evident that the moth is most abundant in the western part of its 

 range, a conclusion which in turn is verified by the losses estimated 

 by millmen in the various sections of this area. 



HOST TREES AND CHARACTER OF INJURY. 



(Figs. 2-5.) 



Douglas fir ( /'.sc.iulot.siif/a ta.ci folia) is evidently the special host 

 of this moth. However, although unable successfully to attack 

 previously uninjured larch (Lari.r occidental is) it breeds also and 

 thrives well in blazes and other wounds on that tree, particularly in 

 the pitch How caused l»y n fungus, identified by Dr. James R. Weir, 

 of the Bureau of Plant Industry, :is Trarrwlrx pini. A great number 

 of fungus-infested larch in :i stand of timber may make this iv^a a 

 peal menace to the Douglas fir in (he same area. 



The healthier and quicker growing ;i Douglas fir may be, the more 

 it appears to he subject to infe tatiou by the moth. Trees are at- 

 tacked when about I" fears old nnd after that until they are about 



