PROCEEDINGS, 1916. 45 



PHYSICAL PROPERTIES 



The arsenate of lime can be bought as cheaply in powder form as in the paste, so 

 most of it is bought as a dry powder. Arsenate of lead, on the other hand comes in paste 

 form for reason of economy. The speed, ease and accuracy of measuring a powder in- 

 stead of a paste into the spray tank at a busy season like spraying time needs only to be 

 mentioned to be appreciated. 



AGITATION. 



In agitating where lead arsenate is used, the lead sulphide sludge holds the poison 

 down and even the best agitators fail to effect complete suspension of the poison. Where 

 arsenate of lime is used there is no lead sulphide to interfere and good suspension of the 

 poison may be obtained by a very inferior agitator. In many case during the season 

 almost perfect agitation of arsenate of lime was found to be effected, where the owners 

 were using the much despised return hose agitator. 



INSECTICIDAL VALUE. 



In regard to efficiency the reader is referred to the article "The Toxic Value of 

 Some of the Common Poisons, Alone and in Combination with Fungicides on a Few 

 Species of Biting Insects," by Prof. W.H. Brittain, and the writer. On the whole arse- 

 nate of lead acts a little more rapidly than arsenate of lime. With sulphide solutions 

 this does not overbalance the reduction in injury secured by the use of arsenate of lime. 



CONCLUSION. 



Arsenic in the form of arsenate of lime is much cheaper than in the form of arsenate 

 of lead. In Nova Scotia arsenic in the form of arsenate of lime will cost less than 

 55 per cent of what it will cost in the form of arsenate of lead. Per content of arsenic 

 there is slight difference in killing power in favor of arsenate of lead. Arsenate of 

 lime is more desirable from every standpoint to use with sulphide sprays. Arsenate 

 of lime should never be used alone on foliage. Lead arsenate is the best poison to use 

 alone. Lead arsenate seems to work slightly better with Bordeaux mixture, but 

 arsenate of lime is cheaper, so that the question of which to choose for use with Bor- 

 deaux mixture is a matter of convenience. 



THE DOCK SAWFLY.* 



Ametastegia glabrata, Fallen; (Taxonus nigrisoma, Nort.) 



By Alan G. Dustan, Assistant Field Officer, and F. C. Gilliatt, Field Assistant. 

 Dominion Entomological Laboratory, Annapolis Royal, N. S. 



ALTHOUGH this insect is considered here in the light of an apple pest, it 

 must be clearly understood that it is such only in a secondary sense, for al- 

 though it sometimes does serious damage to the apple crop, due to its habit of 

 hibernating in the fruit, yet it is by no means dependent on it for its existence and pre- 

 servation through the winter. In the larval stage it feeds solely on one of the members 

 of the Buckwheat family and is found as commonly hibernating in rotten wood, old 

 bark and crevices in the tree trunks, as it is in the apple. 



This sawfly has long been recognized as an orchard pest, just how long we are un- 

 able to say, but Dr. James Fletcher in the thirty-third report of the Entomological So- 

 ciety of Ontario, published in 1902, states that he found it hibernating in apples in Ot- 

 tawa. 



*NOTE — Since this paper went to print, Bulletin No. 265 of the U. S. Dept. of Agric, "The Dock 

 False-worm; an Apple-Pest," by E. T. Newcomer, has appeared, giving the life-history and control of 

 his insect. 



