78 THE GYPSY MOTH APPENDIX. 



By the direction of Professor Fernald, the preceding ex- 

 periments were performed in order to determine the relative 

 iusecticidal effects of Paris green and arsenic on the gypsy 

 moth. While arsenic seems slightly superior to Paris green 

 so far as killing effects are concerned, its high specific gravity 

 renders it difficult of suspension in water, and hence it can- 

 not be applied evenly to the foliage. We have long since 

 abandoned the use of Paris green in our spraying operations, 

 and neither this poison nor arsenic can compete with arsenate 

 of lead as a means for destroying the gypsy moth. The 

 high death rate of the larvte in the check experiments is a 

 probable consequence of the remarkably wet season of 1897. 



SCHEELE'S GREEN. 

 Field Experiment, June 22, 1897. 



Twenty square rods of badly infested oak timber and 

 brush land were thoroughly sprayed with Scheele's green, 

 at the rate of 5 pounds to 150 gallons of water. 



July 1. About 10 per cent, of the larvse are dead. Foliage slightly 



burned. 



July 5 ISTo more larvre dead. Foliage badly burned 

 July 11. Trees stripped by the larwe, except where the foliage has 



been killed by the poison 



In the above experiment the object was to destroy the 

 caterpillars, regardless of the effect upon the foliage. 



