16 BULLETIN 204, U. S. DEPARTMENT OF AGRICULTURE. 



EXPERIMENTS IN DETERMINING THE INCREASE OF THE GIPSY MOTH IN THE FIELD. 



In view of the importance of parasites, disease, and unfavored 

 food plants in reducing the increase of the gipsy moth, it seemed 

 desirable to secure definite data on the normal increase of this insect 

 in the field and the increase where these deterrent elements were 

 present in varying degrees. The most feasible way to determine the 

 increase is to compare the number of egg clusters in a given locality 

 from year to year. In order to do this arrangements were made in 

 the fall of 1911 to study field conditions in a systematic manner. 

 About 250 areas which have been designated as ''observation points" 

 were selected throughout the infested area. This gave an oppor- 

 tunity for ascertaining the effect of latitude, seasonal variation, and 

 altitude on the increase of the species. In selecting these points an 

 attempt was made to secure as many pure stands of forest growth as 

 possible; also, to obtain areas of mixed growth where the proportion 

 of favored food plants varied. Areas were also secured where 

 different species of parasites had been liberated and where the wilt 

 disease had' occurred abundantly or in a small amount during the 

 previous year. The degree of infestation was also considered in 

 making a selection and a number of points were obtained where the 

 trees had previously been defoliated to check against some where no 

 defoliation had resulted and the infestation was very light. After 

 an area was selected a tree was marked for a center and a circle 100 

 feet in diameter was laid out. Each tree within the circle was 

 numbered consecutively and a note made of its species, size, and 

 condition. In the fall, as soon as the foliage had dropped, a careful 

 count was made of the egg clusters on each tree. These results have 

 been secured and tabulated as well as exact information relative to 

 the number of egg clusters found on the ground and undergrowth. 

 Records have also been kept on the condition of the trees from year 

 to year, and the number of trees which died in each area has been 

 carefully noted. The condition of the territory surrounding these 

 points, as regards infestation, has also been noted. This work has 

 been supervised by Mr. C. W. Minott, but it has not been carried on 

 for a sufficient number of years to give all the exact information 

 desired. 



The following table gives the gross number of egg clusters found in 

 the points each year, and will be of interest as indicating in a general 

 way the severity of the infestation from 1910 to 1914. 



It will be noted that 170 points are given in the table. The balance 

 of the 250 which were originally selected have been discontinued, 

 owing to destruction by fire, promiscuous cutting by the owners, or 

 for other reasons. The area in the points aggregates 30.18 acres, 

 and the surrounding territory which has been watched brings the 

 total under observation up to 863.1 acres. For convenience, the 



