2 
This form of injury is due to the attack of the bark maggot (Cheilosia 
alaskensis) subsequent to primary injury by the hemlock barkbeetle 
(Hylesinus n. sp.). 
HISTORICAL. 
In 1902 Mr. Edward T. Allen, of the Bureau of Forestry,! described 
the defect which he had found to be caused by a maggot or larva of an 
unknown fly. 
In 1903-4 the writer made special investigations of the trouble, under 
instructions from Dr. A. D. Hopkins, to determine: (1) The species 
which is responsible for the damage; (2) the life 
histories and habits of the principal species and 
closely related forms, their natural enemies, etc.; 
(3) whether or not the larve are capable of entering 
healthy, uninjured bark; and (4) the character 
and causes of previous injuries which induce attack. 
The principal localities in which the work was 
carried on in connection with that on forest insects 
in general, were Hoquiam, Aberdeen, Satsop, 
Copales, Kent, Puyallup, North Bend, South Bend, 
and Seattle, in the State of Washington, and the 
vicinity of Portland, Oreg. 
The first examination of infested trees was made 
in August, 1908, when maggots of various sizes 
were found to be quite common in the bark of the 
trunks of living trees. Their presence was indi- 
cated by small masses of resin on the surface of 
the bark. In and beneath each of these a single 
Fig: 2-—Box cage fastenea Maggot was at work in a cavity or hole which 
to side of tree to catch extended to the surface of the wood, where there 
ee}: was a wound, evidently caused by this insect. 
Similar wounds, partially healed, and others several years old were 

found in the same trees, from near the outer layers of the sapwood to 
layers deeply buried in the heartwood. The latter were readily 
recognized as the black-check defect and there was no doubt left as to 
their being caused by this insect, which should, therefore, be hereafter 
known as the hemlock bark maggot. 
Experiments with different methods of rearing the adult insect were 
at once started. At first the infested resin masses with a portion of the 
adjoining wood were cut out and placed in jars and tin boxes, but they 
soon dried up or molded. Then cages of netting placed over the resin 
masses on the trees were tried. These proved too flimsy and were hard 
to examine. Finally, cages were made from small baking-powder and 
spice cans, by knocking off the bottoms, cutting the sides into narrow 

1 Bur. For., U.S. Dept. Agric., Bul. 33, ‘‘ The Western Hemlock,”’ pp. 19, 20, 23. 
