760 Journal of Agricultural Research voi.xx.No.io 



sulphate is a fairly satisfactory spray to use; however, because of the re- 

 sistance of conifers to arsenical sprays and because an arsenical treat- 

 ment gives more certain results, it is probable that the spray first 

 recommended should be used almost exclusively. In scattered infesta- 

 tions hand picking or knocking the larvae from the trees and crushing 

 them will be found to be much more economical and at least as effective. 

 Whenever these insects are observed in any locality and control 

 measures ate practiced against them, it is important that the territory 

 be carefully surveyed for the following 14 months, since it is possible 

 that some larvae may have escaped the treatment and have spun cocoons. 

 This possibility makes watchfulness necessary over the entire colony 

 period of the species in order that an emergence of adults from these 

 cocoons may not reestablish the infestation. 



