8 
BULLETIN 1093, U. S. DEPARTMENT OF AGRICULTURE. 
carried by the wind, should be determined by horizontal rather than 
vertical traps. 
A total of 1,288 first-stage larvae were taken on 385 square feet of 
horizontal trap surface, or an average of 3.3 larvae per square foot. 
Table 3 summarizes the information secured on the horizontal 
traps exposed on Muddy Pond Bog during the years 1916 to 1919. 
It will be noted that the number of larvae caught in 1917 far exceeded 
the total for any other year. This was largely due to a slightly 
heavier infestation and more favorable weather for wind dispersion 
when the larvae were in the first stage. 
Table 3. — Wind dispersion data for gipsy moth larvw collated for the four- 
year (1916-19) period. 
Year. 
Number 
of hori- 
zontal 
traps. 
Trap 
surface. 
Total 
number 
of larvae 
trapped. 
Number 
of larvae 
taken 
per 
square 
foot of 
trap 
surface. 
Days of 
disper- 
sion. 
Days of 
heaviest 
disper- 
sion. 
Larvae 
taken 
on days 
of 
heaviest 
disper- 
sion. 
Percent- 
age of 
total 
number 
trapped. 
1916 
4 
7 
9 
1 
Sq.ft. 
240 
385 
500 
55 
Ill 
1,288 
132 
197 
0.4 
3.3 
.2 
3.9 
15 
20 
15 
13 
2 
5 
5 
5 
72 
1,076 
97 
172 
64.8 
1917 
83.5 
1918 
73.4 
1919 * 
87.3 
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Fig. 2. — Showing two daily periods of maximum wind dispersion. 
5 
P. M 
Figure 2 shows graphically the number of first-stage larvae taken 
on the traps during the whole time of dispersion in 1917. This shows 
very clearly the important fact that there are two daily dispersion 
