EFFECT OF TEMPERATURE OX ACTIVITY OF LARVAE. 25 
made to Mr. D. M. Kogers. The hatching thus recorded took place 
in localities which became warm very early in the spring, but this 
serves as a basis for comparing the temperatures. 
The entire period of hatching usually extends over a month. In 
fact, in some parts of the infested territory where the summer season 
is short, owing to the high altitude or to the northern latitude, the 
period is considerably longer. 
Mr. Henry L. Mclntyre, one of the general foremen in charge of 
moth work for the Bureau of Entomology, informs me that several 
unhatched gipsy-moth egg clusters were found July 1, 1910, at 
Winchendon, Mass., by scouts who were working under his direction. 
The clusters were well formed and were apparently fertile, although 
this point was not fully determined. 
He also reports that in the spring of 1908 he found egg masses 
in maple swamps near Portsmouth, N. H., that had not hatched on 
June 15. In 1909 he observed several egg clusters that had just 
hatched in a stone wall at Gilford, N. H., on June 4. 
This shows the variation in time of hatching in different localities 
and situations, but it is exceptional for hatching to take place after 
June 1. Additional data on the dates of hatching have been fur- 
nished by Mr. F. A. Bates, who has for many years been prominently 
connected with moth work, and from various other careful observers. 
The accompanying diagram (fig. 1) shows the range in tempera- 
tures for 20 days preceding and 10 days following the first report of 
hatching for the years 1908 to 1911. It will be noted that in 1910, 
when hatching was recorded April 3, nearly two weeks of warm 
weather immediately preceded hatching. In 1909 the warm weather 
was interrupted by several cold days, while in 1908 and 1911 hatching 
took place during the only warm period that occurred in the month. 
This last record shows the tendency of the eggs to hatch at the first 
opportunity as the season grows late. 
EFFECT OF TEMPERATURE ON ACTIVITY OF LARViE. 
As the activity of the caterpillars after hatching as well as their 
emergence from the eggs depends upon the temperature, several ex- 
periments were made to determine the temperature at which the 
larva? are most active, since it is obvious that little distribution by 
wind would be possible unless the larvae were active during the first 
stage. Accordingly, a series of laboratory tests were made by Mr. 
Collins. For this purpose a constant-temperature incubator was 
used, it being arranged in such a way that the thermostat which 
regulated the heat supplied by electric incandescent lamps could be 
changed without opening the incubator. 
