This form of injury is due to the attack of the bark maggot {Oheilosia 

 alashensis) subsequent to primary injury by the hemlock barkbeetle 

 {Hylesinus n. sp.). 



mSTOBICAIi. 



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 r'elated forms, their natural enemies, etc.; 

 (3) whether or not the larvae 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, 1903, when maggots of various sizes 

 were found to be quite common in the bark of the 

 trunks of living trees. Their presence was indiT 

 cated by small masses of resin on the surface of 

 the bark. In and beneath each of these a single 

 Fm. 2.-B0X case fastened 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 

 a ut y origina . ^^^ ^ 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 insept, 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 



Bur. For., U. S, Dept. Agric, Bui. .33, "The W- 



