182 
JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
work required the services of about 25 men for 3 months and the data 
was recorded and classified on special forms prepared for that purpose. 
The egg clusters were rated as large, medium or small at the time of 
counting so that it was possible to determine rather accurately the 
potential crop of caterpillars for the next season. In badly infested 
points hundreds of egg clusters were frequently found on a single tree so 
that the time required for making an accurate count was considerable. 
Test collections of eggs and caterpillars were made just outside the 
points to determine the effect of parasitism on the increase. These were 
examined or reared at the Laboratory and the rate of parasitism com¬ 
puted. 
During the summer the points were visited and information secured on 
the abundance of disease and its effect on the increase of the species. 
In order to obtain more accurate data on what was actually happening in 
the field several points were selected and after careful counts of egg 
clusters had been made the ground beneath the trees was covered with 
canvas mats. These were examined daily and all caterpillars that 
dropped w r ere examined and the causes of death determined and tabu¬ 
lated. The mats required almost constant attention in order that 
the number of dead larvae might be recorded before they were carried 
away by ants or other insects. Later a census was made of the con¬ 
dition of the trees as to mortality of caterpillars or pupae, the amount of 
defoliation and the next brood of egg clusters. 
Experience showed that these methods failed to give accurate results 
principally because a considerable proportion of the small caterpillars 
were blown from the areas if winds were favorable during the spring and 
this affected the count records for the following year. In cases of over 
population and w T here defoliation resulted many of the large caterpillars 
migrated for food. If the temperature was too severe in the winter 
many of the egg clusters that were unprotected by snow or ice failed to 
hatch. 
This caused a modification of the plan which resulted in less stress 
being placed on the actual number of egg clusters in the points and more 
on the result of feeding by the caterpillars. 
Check records of trees that were actually climbed and those where the 
infestation was estimated after a partial count made from the ground by 
men having long experience in this particular w r ork, showed that reason¬ 
ably accurate data could be secured and much time could be saved. 
The method was changed accordingly and what is known as an estimate- 
count of each tree replaced the plan at first used. The records have 
been kept as heretofore. 
