METHODS EMPLOYED AGAINST GIPSY MOTH. 17 



bodies. Many colonies were discovered on the premises of milkmen 

 and market gardeners who made regular trips to the infested section 

 to distribute their products. 



, SPRAYING. 



It was at first beUeved that this insect could be successfully con- 

 trolled, like most other leaf-eating species, by spraying the trees with 

 Paris green, a remedy which was then in common use. Experiments, 

 however, showed that it was impossible to kill the caterpillars with this 

 spray after they became half grown, unless it was used so strong 

 that it resulted in severe injury to the foliage of the trees. Mr. F. C. 

 Moulton, who conducted an extensive investigation with insecticides 

 in the years 1891 and 1892, was able to prepare a new insecticide, arse- 

 nate of lead, which could be used in sufficient strength to kill the 

 caterpillars without injuring the foliage. This work was later taken 

 up by Messrs. A. H. Kirkland, F. J. Smith, and A. F. Burgess, under 

 the direction of Prof. C. H. Fernald. A large number of experiments 

 were made, using different formulas, which demonstrated the practical 

 effectiveness of this poison and the proper method of its preparation. 

 The poison as used at that time was made by dissolving the proper 

 amounts of arsenate of soda and acetate of lead salts in separate ves- 

 sels containing water. These solutions were then brought together 

 and a precipitate, consisting of arsenate of lead, was formed. Usually 

 the fresh precipitate was prepared in the field. In recent years, since 

 this poison has come into general use throughout the country for treat- 

 ing trees infested with leaf-eating insects, it is made by manufacturers 

 in a similar way, and is put on the market in the form of a paste which 

 mixes readily with water, thus preventing the delay occasioned by 

 mixing the raw chemicals and obviating the danger of securing impure 

 materials, which might cause injury to the foliage or crop treated. 



Some improvements were made in spraying machinery, which was 

 very crude when we consider the equipment used at the present time. 

 Spraying with the facilities then at hand was a very expensive opera- 

 tion, and in many cases gave unsatisfactory results, especially when 

 large trees were treated. Owing to these facts, and because every 

 effort was being made to secure the extermination of the insect, 

 spraying was undertaken only in a limited way. 



BURLAPPING. 



The secretive habits of the caterpillars suggested the provision of 

 artificial hiding places, and for this purpose burlap bands were placed 

 about the trunks of the trees. Bolts of burlap were cut into strips 

 about 8 inches wide, which were rolled for the convenience of the 

 workmen. A band was placed around each tree about as high as a 

 40705°— Bull. 87—10 2 



