12 BTLLETIX 1093, U. S. DEPARTMENT OF AGRICULTURE. 
to the square foot would materially reduce the crop and would 
necessitate flooding or spraying in order to prevent damage 
Plate VI, Figure 1, shows a section of the surf ace of the vines in the 
above-mentioned pen and when compared with Plate VI. Figure 2. 
showing a similar area just outside of the pen, on the bog proper, 
with the vines in full bloom, the loss of the new growth is manifest. 
MORTALITY OF FIRST-STAGE LARViE. 
General observations on Muddy Pond Bog, particularly in connec- 
tion with the pen experiments, have shown that there is a varying 
percentage of mortality among the several larval stages of the gipsy 
moth, after they reach the cranberry vines. This mortality is prob- 
ably greatest in the first stage, owing to several factors. The princi- 
pal factor is reduced vitality, since larvae hatching from egg masses 
that were deposited upon conifers or other nonfavored food species 
had used up a considerable percentage of their vitality in searching 
for food before they were blown from the tree onto the vine surface. 
Their vitality was further reduced in crawling over the vines before 
approaching starvation finally forced them to feed upon the buds or 
new stalks of the cranberry vines. While in this weakened condi- 
tion the larvae are more susceptable to cold, particularly when ac- 
companied by rain. That there is quite a difference between the 
temperature at the tops of trees and that at the bog surface was 
demonstrated by the use of recording thermometers. The platform 
at the top of the tower constructed around the white oak tree on 
which feeding observations were made was about 50 feet above the 
bog level. A comparison of the thermometer records made at the 
top of the tree and at the surface of the bog shows that the tempera- 
ture averaged 5.2° F. cooler at the bog surface than at the top of 
the tree for the night period during the 6 days of heaviest wind dis- 
persion, viz, May 25 to 30, inclusive. From 6 p. m. May 29 to 5 a. m. 
May 30 the average temperature was 11.3° F. lower at the bog sur- 
face than at the top of the tower. At 1 a. m. May 30 it was 15° F. 
lower at the surface of the bog than in the tree top, the maximum 
difference in the locations during the period. This was the coldest 
night of the period, and gave the greatest range of temperature. 
The above temperatures were obtained from the thermometers in 
latticed shelters. 
There is also a high mortality among first-stage gips}^ moth larva? 
on cranberry bogs due to disease, predacious enemies, and other 
causes that are not well understood. All of these agencies, together 
with the rather unfavorable nature of the cranberry foliage as a food, 
combine to bring about an enormous reduction of the wind-blown 
larvae. 
