15 



to all those from whom I have received advice and actual 

 assistance. My thanks are also due to State Forester Frank 

 W. Rane and Assistant Forester L. H. Worthley for much 

 help ; and to their division agents, Norman Souther of Bridge- 

 water, and Francis C. Worthen of Georgetown, and to Mr. 

 H. P. Richardson, local moth superintendent of Concord, for 

 their support in the field work. Last but not least, I owe, 

 through correspondence, several valuable hints to Dr. E. Fischer, 

 Zurich, Switzerland, who, through his investigations on insect 

 diseases, is to be regarded the proper instigator of these ex- 

 periments. 



In the beginning of the work each of the division agents was 

 asked by letter to suggest convenient localities in which to con- 

 duct the experiments. Three of the division agents stated 

 that they had no suitable places in their districts. In the 

 remaining divisions 29 places were chosen, but at the end of 

 my investigations unfortunately 13 of these could not be used, 

 since some of the local moth superintendents had not followed 

 instructions, and other places had been sprayed with arsenate 

 of lead. Isolated forest districts, varying from small areas 

 to several acres, were chosen for the experiments. The isola- 

 tion was for the purpose of making easier a control of the 

 place, since in such a locality an eventual increase or decrease 

 of the caterpillar mass by migration was less probable. The 

 local superintendents of the different places were instructed not 

 to use any artificial means for destroying caterpillars in the 

 selected woods. I was, however, obliged to use some localities 

 in which, during the preceding winter, some of the egg clusters 

 had been killed by creosote. According to the size of the 

 various places, the local superintendents were requested to col- 

 lect a corresponding mass of gypsy moth caterpillars shortly 

 before their second molt. These amounted to from 50 to 100 

 individuals per acre. Where many egg clusters were present 

 but few caterpillars had to be collected, and vice versa. Hence, 

 the number of caterpillars to be collected was decided in ad- 

 vance for each locality. The reason for this is that an in- 

 fection spreads more easily and rapidly in a heavily infested 

 district than in places less damaged by caterpillars. In a 



