83 



of diffusion and absorption by soil water, the alteration of concentration 

 of the gas caused by soil particles, and its decomposition by certain 

 soil constituents. 



Experimental investigations on these points have shown that the 

 toxicity of hydrocyanic gas solutions varies with the insects 

 experimented upon, from the minimum for house-flies {Musca domestica) 

 of "0156 gm. sodium cyanide per htre (equivalent to "0046 per cent, of 

 hydrocyanic acid gas over the solution) to the maximum for beetles 

 {Diabrotica soror) of "125 gm. per litre (equivalent to '0365 per cent, of 

 hydrocyanic acid gas over the solution), the latter being the most 

 resistant of any insect experimented upon. The gas at a concentration 

 fatal to house-flies only slightly retards the germination of lettuce 

 seeds, which were not killed even by a two days' exposure to gas 

 nearly three times as strong as that toxic to beetles. In the case of 

 seedlings it was found that a solution 256 times as strong as that 

 producing gas toxic to flies killed all the seedUngs and half of the 

 cuttings placed in it, while a solution twice as strong as that required 

 against flies had no effect even ujDon seedlings. In short, a dosage 

 toxic to flies and Phylloxera would be safe for all plants experimented 

 upon, while that necessary for beetles, would be extremely dangerous 

 if not fatal. 



As regards the introduction of the gas into the soil, it was found 

 impossible to effect this by injecting sodium cyanide solutions into 

 the ground, or by forcing in the gas under pressure, owing to soil 

 and water both being strong absorbents of the gas. Eetention of the 

 gas depends upon the character of the soil, a heavy, damp or very wet, 

 sandy soil being almost impervious to the gas, which is taken up by a 

 pure sandy soil only in proportion to the amoimt of water present, and 

 in a clay soil is either decomposed or changed in concentration by the 

 soil particles. Attempts to generate the gas in the earth showed that 

 it diffuses with extreme slowness in clay soils or very wet sandy soils, 

 but much more rapidly in fairly moist sand. 



The conclusion reached is that sodium cyanide affords a satisfactory 

 means of fumigating masses of loose, porous soil, especially those 

 containing little clay, also seed-beds and potting soil, but that the cost, 

 while comparable ^dth that of carbon bisulphide fumigation in light 

 soils, is not within the range of economy except in small areas, even 

 when the value of the gas as a nitrogenous fertiliser is considered, the 

 fumigation of heavy soils being very much more expensive. 



Hewitt (C. G.). Report of the Dominion Entomologist for the Year 

 ending 31st March 1917. — Dominion of Canada, Dept. Agric, 

 Ottawa, 1917, 24 pp. [Eeceived 29th December 1917.] 



The arrangement whereby the Governments of the provinces of 

 Nova Scotia and Biitish Columbia under supervision of the Department 

 of Agriculture carry out fumigation of foreign nursery stock destined 

 for those Provinces is proving very satisfactory. Details are given of 

 inspection work in connection with the control of brown-tail moth 

 [Nygmia pJiaeorrhoea, Don.], in Nova Scotia and New Brunswick. In 

 continuation of the work of colonisation of parasites of this pest and 

 of the gipsy moth [Lymantria dispar], no less than 15,725 puparia of 



