April, ’24] 
burgess: estimating gipsy moth abundance 
181 
readily found by anyone experienced in controlling this insect. | The 
caterpillars feed on most deciduous and some coniferous foliage and the 
female moths do not fly. 
From the foregoing statement it would appear that this insect was an 
ideal subject for making a study of the rate of increase in the field and 
the damage resulting from its work. The importance of having accurate 
data along this line was such that preliminary work was begun in 1911 
and an intensive study was taken up in 1912, Data have been collected 
during each year since that time, although the methods of securing the 
information have been modified as experience on the work and the dis¬ 
covery of new information made changes advisable. 
The question of increase of an insect cannot be solved satisfactorily by 
laboratory methods or theoretical computations. It is necessary to 
secure the data in the field under normal natural conditions. The two 
main purposes covered by the experiment was to determine the rate of 
increase and factors affecting it and the damage resulting from defolia¬ 
tion. The methods used will be considered separately. They are not 
intended for the use of observers who desire to report on conditions 
covering a large area such as a state or group of states but for securing 
reliable data relating to what is actually happening in the field. 
Selection of Observation Points 
Two hundred and fifty areas in the infested region in Maine, New 
Hampshire and Massachusetts were selected. These were in different 
mixtures of forest growth and where different degrees of infestation were 
present. A central tree was selected which was bounded by a circular 
area with a radius of 50 feet, making each area about one-fifth of an 
acre. Each point was numbered and detailed records have been kept 
since the experiment started. 
Each tree in an observation point over 3 inches in diameter was 
numbered consecutively about breast high with white paint, the highest 
number being placed on the north side of the center tree. All numbers 
faced toward the latter tree. The undergrowth which was unnum¬ 
bered was listed according to species. 
i 
Method of Collection of Data on Increase 
Counts of all egg clusters in each point were made during the fall. 
This necessitated climbing the trees and an examination of the litter on 
the ground as eggs are frequently deposited in such situations. This 
