20 THE REPOET OF THE No. "36 



m the cases in which the nursery stock was shipped, as well as the cases. 

 After the trimmings from the fruit seedlings had been burned, as an extra pre- 

 caution the importers were advised to dip the stock in kerosene emulsion, or a 

 standard miscible oil as was being done in New York State. Tf the packing, etc., 

 from these cases wej-e not destroyed before spring, it can be readily seen how some 

 of these caterpillars might have got out and established themselves. 



In the report of the Division now in press there will also be found a state- 

 ment of some experiments with hydrocyanic acid gas to kill the larvse of the Brown- 

 tail Moth. These experiments were conducted in a fumigation box having 128 

 cubic feet of contents. Varying strengths of gas were tried, from the one used 

 in the federal fumigation houses to destroy the San Jose Scale, viz., 1 ounce of 

 cyanide of potassium, 1 ounce of sulphuric acid and 3 ounces of water to every 

 100 cubic feet of air space, exposure 45 minutes, to three times this strength, the 

 exposure being lengthened to 2 hours. In these experiments many of the larv?e 

 had left the nests and were active on the sides of the glass jars, with cheese cloth 

 coverings, in which they had been kept. These experiments, although not very 

 extensive, went to show that fumigation with hydrocyanic acid gas evidently can- 

 not be relied upon as a practical remedy for this insect when in its winter condi- 

 tion. Even when the strength of the gas was three times that used in our federal 

 fumigation houses, and the exposure very much lengthened, only a very small per- 

 centage of the larvae which had left the nests were killed. It would certainly require 

 considerably greater strength and much longer exposure to kill the larvse when 

 within the nests, and owing to the tough, closely woven nature of these nests the 

 outcome would be very doubtful. In this work of fumigation I was assisted by 

 Mr. Herbert Groh. 



THE LAEGE LAECH SAWFLY. 



(Nematus Erichsonii, Hoirtig.) 



Dr. C. Gordon Hewitt^ Dominion Entomologist, gave a brief description of 

 his work on this insect in England, where it is becoming a serious forest pest. 

 Its distribution in Canada is also increasing and the larches (Larix americana) as 

 far west as Winnipeg, are now suffering from the attacks of this sawtly, which 

 destroyed most of the larches in Eastern Canada subsequent to its appearance in 

 1882. 



Only one brood was found to occur — the deposition of the eggs and the emer- 

 gence of the larvae extended over a considerable period, and might give the im- 

 pression that the species was double brooded. 



The chief parasite was found to be Mesoleius aulicus, Grav., and investigation 

 showed that in 1908 the average number of cocoons parasitised was 6 per cent., in 

 the present year it was found to have doubled. Another ichneumon, Microcrypius 

 labralis, Grav., was bred out and this insect is probably a hyper-parasite on 

 (M. aulicus.) 



One of the most potent factors in the natural control of the insect was the 

 Field Vole {Microtus agresiis,) which extracted the larva from the cocoons during 

 the winter, during which season the larvae form a large portion of their food. 

 In one plantation about 50 per cent, of the cocoons were emptied in 1908 by these 

 rodents. 



