6 BULLETIX 1080, U, S. DEPARTMENT OF AGEICULTUEE. 



first year could be compiled and studied it became evident that 

 humidit}- could play little, if any, part in the killing of the eggs. 

 As stated elsewhere, the factor responsible for nonhatch acts during 

 the cold months of December, January, and February, during which 

 the amount of moisture in any given space is xery low. This in 

 itself would hardly be proof, as low humidity might have some 

 eifect. There was no appreciable difference, however, between the 

 humidity records from the three points, two of which showed non- 

 hatch while none was obtained from the third. Humidity records 

 for succeeding years have only served to substantiate those obtained 

 the first year. 



Temjjerature lines for the three points followed one another 

 closely until December, but as soon as severe cold weather set in 

 the difference became very marked. 



At the point which had never yielded nonhatch the coldest days 

 found the mercury little below zero, while at the other two. tempera- 

 tures of from — 20° F. to — 30° F. were recorded, and during most 

 of the time they were from 15° to 25° colder than the first point. 

 The two exceptions to this were during December, 1917. and Febru- 

 ary, 1920. when the temperature at the warmest point fell to —15° 

 and —16° F., respectively, for the only times during the four years 

 that records have been taken. These resulted in many eggs failing 

 to hatch. 



Temperature records obtained from the instruments during four 

 consecutive winters show that the cold weather comes from the last 

 part of December to the first of March, with the lowest drops in 

 January and Februarv'. The first winter, 1916-17, was only moder- 

 ately cold, with the greatest drop coming in February. The next 

 winter, 1917-18. was extremely cold in December, January, and 

 February, and following this ftame the unusually mild winter of 

 1918-19 with hardly a drop below zero. This in turn was followed 

 by another extremely cold winter which made conditions almost 

 ideal for our experiments. The mild winter of 1918-19, coming as 

 it did between two that were very cold, made comparison of the 

 records of all three seasons very valuable. 



The "Weather Bureau office at Boston obtains records regularly 

 from 50 substations in the gipsy-moth area. A study of these rec- 

 ords shows that in general the drops in temperature become lower as 

 one goes northward. Along the coast, however, due to the modify- 

 ing effect of the ocean, the cold is nowhere nearly as severe as it is 

 farther inland. Also, one may find small areas having much lower 

 temperatures than the surrounding country, due to the topography 

 which induces that phenomenon known as air drainage, the cold air 

 flowing down into the lowest spot and settling there. 



RESULTS OBTAINED FROM EXPERIMENTS. 



Monthly collections, as stated on page 3. were made at five chronic 

 nonhatch points and one control point where no nonhatch had ever 

 been found. Three of these had weather instruments, so that it was 

 possible to check results against temperature records. 



