34 



forest from the two localities in which the experiments were performed. 

 However this may be, the wilt had acted at any rate in such a virulent 

 manner that in all these 30 acres of forest not a single fresh egg cluster 

 could be found, notwithstanding the most painstaking search on ' the 

 part of Mr. Worthen and myself. 



Mr. Worthen also undertook, on his own behalf, the breeding of sev- 

 eral hundred caterpillars, feeding them according to my instructions. 

 The disease could be noticed in this brood as early as June 14, 1910. 

 Most of these caterpillars had just passed the third molt. Three days 

 later he exposed all the material among the caterpillars of a forest near 

 his home. Soon he observed the " dying off " of the caterpillars which 

 were there present. The number of the dead ones grew astonishingly, 

 but the final result cannot be stated, since, unfortunately, the trees 

 were later sprayed with arsenate of lead. 



West Bedford, Mass. 



The division agent and the local superintendent in this locality were 

 not requested to perform the experiments. My friend, Mr. L. W. 

 Swett, the well-known specialist in Geometridae, asked me in the spring 

 of 1910 to undertake an experiment with the wilt upon his estate on 

 Davis Street, northeast of the railroad station, in West Bedford. We 

 inspected the place for this purpose on May 29, and the locality ap- 

 peared to be a very suitable one for the work. It consists of two iso- 

 lated strips of wood, which meet at a right angle. One strip comprises 

 oaks about fifty years of age, mixed with some brush; while the other 

 consists of dense birch brush about six years old. The whole locality 

 comprises about three-quarters of an acre. The gypsy moth was first 

 discovered here in 1908, and the place since that time has been under 

 continuous observation by Mr. Swett. He assured me that there were 

 positively no signs of a disease among the caterpillars. During the 

 summer of 1909 the caterpillars were quite numerous. Part of the egg 

 clusters, which were laid in the autumn of 1909, were killed with 

 creosote, but there were still present, according to Mr. Swett's and my 

 estimation at the time of my first visit, about 400 clusters on the oaks 

 and about 100 clusters on the birches. 



The caterpillars for this experiment were raised by the author at 

 Forest Hills. They began to die from Flacherie after a continuous 

 feeding of fourteen days, and just as they had passed the third molt. 

 This material was planted, June 22, 1910, in the birch brush, and the 

 bag was fastened about 6 feet from the ground. Most of the cater- 

 pillars of this locality were at that time half way between the third 

 and fourth molt. The place was visited again on July 18, 1910, to 

 determine the progress of the disease. Mr. Swett and I found that 

 the caterpillars were dying in considerable numbers, and the percentage 

 of dead individuals was greatest on the shortest brush, and decreased 



