142 



THE GYPSY MOTH. 



is arsenate of lead, a poison slower in its action than the 

 other, but which has three distinct advantages: (1) It can 

 be used at any desired strength without serious injury to 

 the foliage; (2) It is visible wherever used, as it forms 

 a whitish coating on the leaves ; (3) It has adhesive quali- 

 ties, given it, probably, by the acetate of lead, and therefore 

 remains on the leaves for a much longer period than Paris 

 green. When sufficient glucose was added to a strong mixt- 

 ure of arsenate of lead, it withstood rainstorms and remained 

 on the foliage during an entire season. 



When in 1891 it became evident that the arsenites would 

 not accomplish the desired result, other means of destroying 

 disjpar were sought. Yet it could be hardly credited that 

 the larva was indifferent to the action of arsenical poisons as 

 ordinarily used, and the experiments of 1891 were duplicated 

 during the season of 1892. They were performed by Pro- 

 fessor Fernald and his assistants, but the results of these 

 experiments confirmed those of 1891. 



When it was seen that the known arsenites could not be 

 used at the requisite strength for killing gypsy-moth cater- 

 pillars without serious injury to the foliage, Mr. F. C. 

 Moulton, one of the inspectors employed in the field, who 

 was also a chemist graduated from the State College of Agri- 

 culture and Mechanic Arts, Orono, Me., was detailed to make 

 experiments to determine what portion of the compound 

 produced the caustic efiect upon the foliage. The results 

 of the experiments confirmed the conclusions of previous 

 experimenters that the soluble arsenic burned the foliage. It 

 was obvious that if a form of arsenic entirely and quickly 

 soluble in water could be precipitated, it would become 

 insoluble and obviate the burning. 



In the winter of 1892-93, at a hearing before the legis- 

 lative joint standing committee on agriculture, a bill for the 

 destruction of caterpillars within the State was considered. 

 At this hearing Mr. Andrew H. Ward proposed the use of 

 arsenate of soda as an insecticide. At the hearing we ob- 

 tained from Mr. Ward the particulars in regard to the price 

 of arsenate of soda and where it could be procured. 



Upon consultation with Professor Fernald (who had also 

 been previously asked by Mr. Ward to try the insecticide 



