April, '11] RUGGLES: LARCH SAWFLY 171 



THE LARCH SAWFLY IN MINNESOTA 



By A. G. RuGGLEs 



The northern part of Minnesota has an enormous acreage in timber, 

 and will have for a number of years to come, in spite of the forest 

 fires and normal cutting processes. It has been impossible to deter- 

 mine the amount of tamarack in this region, although a number of 

 foresters famiUar with the tamarack areas have been questioned. 

 An estimate given ran up into the millions of dollars. 



When the Larch Sawfly began its depredations in 1908 there was 

 great concern among the lumbermen. The presence of this insect 

 was first noted in August, 1909, though from the dead and dying 

 tamaracks seen the pest must have been at work during the two or 

 three preceding years. At the present time there are, to my knowl- 

 edge, three areas of infestation in Minnesota, — one at Itasca Park 

 (a thirty-five-square mile tract around Lake Itasca, the source of the 

 Mississippi), one at Cloquet, where the State Forestry Experiment Sta- 

 tion is located, and another near Ely in the United States Government 

 reserve. Unfortunately the writer has examined personally only 

 the area at Itasca Park, and there not in the breeding season, but each 

 of two years just as the larvae were leaving, or had, for the most part, 

 left the trees. 



The work on the insect has been done almost entirely in the insec- 

 tary. Several hundred cocoons were gathered in the spring of 1910, 

 but from this number only 125 adults were reared, and of these it is 

 interesting to note that three were males, a larger percentage than 

 Doctor Hewitt found in his work on the Larch Sawfly in Europe, 

 although perhaps with a larger number reared a smaller proportion 

 of males might have appeared. 



One species of Hymenopterous parasite was reared, which occurred 

 in large numbers. I estimated that 10 to 15 per cent of the cocoons 

 showed the presence of this parasite. Mr. C. T. Brues identified it as 

 Diglochis sp. 



Prof. R. H. Pettit, of East Lansing, Mich., learning that work was 

 being done on this sawfly, kindly sent me a fungous preparation to 

 scatter among the larvse as they were descending the trees to enter 

 the soil. Unfortunately, this fungus arrived after the cocoons were 

 well formed, but in spite of this a few experiments were started, and 

 by September 1 the fungus had spread considerably. This fungus, 

 however, seems to be almost identical with the one found by me this 

 summer under natural conditions. In one small area I found as 

 many as 5 per cent of the 1909 cocoons infected. 



