20 



Cluster 6. 



Unfertilized eggs, . . ~ I = .79 per cent., or about 1 per cent. 



Eggs with dead embryos, • 3 J 



Eggs apparently aUve, . . 377 =99.21 per cent., or about 99 per cent. 



Total, .... 380 eggs. 



The average of these 5 clusters is as follows : — 



Dead eggs, ... 4 = .92 per cent., or about 1 per cent. 



Eggs apparently aUve, . 433 =99.08 per cent., or about 99 per cent. 



Total, .... 437 eggs. 



The results of this control experiment are used in estimating 

 the departure from the normal of the egg masses in all the 

 other experiments. 



B. The Single Expeeiments. 



Concord, Mass. 



Division Agent, Chas. W. Minot; Local Superintendent, Henbt P. 



RiCHABDSON. 



As a suitable place for my experiments, I located, on May 20, 1910, 

 an isolated forest of about 2% acres, belonging to the estate of Mr. 

 William Brewster. This place is situated in the eastern part of Con- 

 cord, about half a mile west of the "West Bedford railroad station. 

 The forest consists mainly of oaks about twenty years old and of a 

 group of pines about fifty years old, all mixed with brush; and along 

 the border, especially on. the northern part, are birches about ten years 

 old. 



According to the local superintendent and to the owner, Mr. Brewster, 

 the gypsy moth caterpillars were quite numerous during the summer 

 of 1909. Both are certain that there was no disease among the cater- 

 pillars. We estimated this place to contain about 10,000 clusters of 

 eggs in May, 1910. 



On June 6 I received notice from the local superintendent that the 

 wilt had appeared among the caterpillars which he had collected and 

 fed according to instructions. Two days later I went to Concord, and 

 found that some 10 caterpillars were already dead and the others were 

 apparently very sick, as they remained motionless even when irritated. 

 The superintendent had begun to feed the caterpillars on May 26, and 

 had noticed the first dead specimen on June 5. Accordingly, he had 

 succeeded in developing the wilt aftiflcially in the course of eleven days. 



