32 



BULLETIN 351, U. S. DEPAKTMENT OF AGRICULTURE. 



Migration to the Twigs. 



The twigward migration of the females starts about the 1st of 

 August and reaches its maximum before the middle of the month, after 

 which it continues in a small way until the leaves fall. In the 

 vicinity of Mont Alto, Pa., from 80 to 90 per cent migrate between 

 August 8 and August 20. (PL I, fig. 4.) 



Table XXIV gives data from observations made upon 1,494 

 migrating females during 1912 at Mont Alto, Pa. The observations 

 in Part I were made upon larvae that settled naturally upon orchard 

 trees. The material considered was isolated with tree tanglefoot 

 August 1 and the females as they migrated were removed and counted 

 at two-day intervals. The age at which these particular larvae 

 migrated is not definitely known, but was about 40 days. The rear- 

 ing of July 22 (Part II) migrated from the thirty-ninth to the fiftieth 

 day after emergence, and made its maximum daily migration August 

 30, which was the thirty-ninth day. The rearing of August 9 (Part 

 III) migrated from the thirty-first to the fifty-seventh days and 

 made its maximum daily migration upon September 15, which was 

 the thirty-seventh day. It is evident from a comparison with figure 

 11 that the maximum in Part III was retarded. A cold wave, 

 which started September 7, retarded the maximum daily migration, 

 causing it to be nearly a week after the start. 



Table XXIV. — The time of the twigward migration of 1 ,483 female larvse of the terrapin 

 scale, Mont Alto, Pa., 1912. 









Twigward migra- 









Twigwarc 



migra- 









tion. 









tion. 





Material 

 observed. 



Num- 

 ber of 

 larvae. 





Part. 



Material 

 observed. 



Num- 

 ber of 

 larvae. 







Part. 





Num- 





Num- 









Date. 



ber mi- 

 grated. 









Date. 



ber mi- 

 grated. 



I 



Orchard larvse, 



976 



Aug. 12 







III... 



Rearing of Aug- 



294 



Sept. 8 









Mont Alto, 





14 



283 





ust 9. 





9 



2 





Pa. 





16 



18 



20 



22 



24 



26 



28 



30 



Sept. 1 



3 



5 



176 



202 



120 



65 



33 



32 



24 



13 



10 



12 



6 









10 

 11 

 12 

 13 

 14 

 15 

 16 

 17 

 18 

 19 

 20 



5 

 13 

 24 

 23 

 18 

 65 

 20 

 18 

 20 

 11 

 24 



II, . . . 



Rearing of July 



213 



Aug. 30 



61 









21 



5 





22. 





31 



Sept. 1 

 2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 

 11 

 12 



19 

 6 



50 



20 



17 



14 



10 



7 



4 



3 



2 













Total .. 





22 



23 



24 



25 



26 



27 



28 



29 



30 



Oct. 1 



2 



3 



4 



5 



10 

 5 

 8 

 9 

 3 

 3 

 1 

 

 





 

 

 6 





1,483 











