8 



BULLETIjST 1093, U. S. DEPARTMEXT OF AGRICULTUEE. 



carried by the Tvind, should be determined by horizontal rather than 

 vertical traps. 



A total of 1^88 first-stage larvse 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 Jarvre co'Uated for the four- 

 year i J 916-19} period. 



Year. 



Number 

 of hori- 

 zontal 

 traps. 



Trap 

 surface. 



Total 

 number 

 of larvae 

 trapped. 



Number 



of larvse 



taken 



per 



square 



foot of 



trap 



surface. 



Days of 



disper-' 



sion. 



Days of 



heaviest 

 disper- 

 sion. 



Larvae 



taken Percent- 



on days | age of 



of , total 



heaviest i number 



disper- ^ trapped. 



sion. 



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 



1 

 72 64.8 



1917 



1,076 83.5 



1918 



97 73.4 



1919 



172 1 87.3 











240 

 220 



Zoo 



V l6o 



6o 

 Ac 

















1 









Lari 



/ae. fe. 



\ke.n o 



rr /ra^ 



xs -/^ 



^/3tJ ^6) 



1i2.JijU2bJ4-.JS. 



?/7. 



















' 































































tto 



tZA 













































































































171 













































































1 -.. 





















1 1 A 



121 



1 1 A 





































































































75 















7o 











fo/ 











31 















51 



































































































































9 10 



A.M. 



)l 



12 I t 3 4- 



Hour^ of Day — 



Fig. 2. — Showing two daily periods of maximum wind dispersion. 



s e, 

 P. M 



Figure 2 shows graphicallj- the number of first-stage larvse 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 



