THE TERRAPIN SCALE. 



31 



In the orchards at Mont Alto, Pa., in 1912, the maximum molt was 

 upon the fortieth day. In all the rearings there was a very short 

 interval between the first molt and the maximum daily molt. This 

 interval varied from 2 to 5 days, with 3 days as the normal time. 



In 1913 observations were made upon two rearings, one of which 

 emerged June 24. This rearing of 174 females made its maximum 

 daily molt upon the thirty-ninth day. Reference to Table XXII 

 will show that the first molt for this rearing was made upon the 

 twenty-second day. It was slightly delayed by a storm, but the 

 larvae reached the maximum of the second molt on the thirty-ninth 

 day; that is, 1 day ahead of the average time for the orchard larvae. 



Table XXIII. — Age of the terrapin scale at the second molt as determined from the maxi- 

 mum daily molt. 



Year. 



Material. 



Number of 

 specimens. 



Age at the 

 maximum 

 daily molt. 



Weather conditions. 



1912 



Brood of July 22 



213 



100 



1,765 



Days. 

 38 

 38 

 37 



Unfavorable. , 







Do. 







Do. 













37.1 













1913 



174 

 69 

 190 



39 

 37 

 36 



Favorable. 





Brood of June 26 



Do. 





Brood of orchard 1 



Do. 









37.3 











1 These data refer to larvae reared upon isolated twigs at Mont Alto, Pa., and not to the entire orchard 

 brood. 



The foregoing data show that the averages for the two years differ 

 by only two-tenths of a day. Some of the individuals, however, 

 departed 4 or 5 days from this average, while in 1912 some specimens 

 made the molt as late as the forty-second day and in 1913 some made 

 it as early as the thirty-second day. 



Leaf Phase of the Third Instar. 



After molting to the third instar the females remain motionless on 

 the underside of the leaf for a period of 1 day while they secrete a 

 very thin dorsal scale which protects them during migration to the 

 twigs. 



The individuals vary in size in the same season, and there is a 

 slight variation in the average size from year to year. The measure- 

 ments from 11 specimens showed a minimum length of 1.387 mm. 

 and a minimum width of 0.862 mm. ; a maximum length of 1.65 mm. 

 and a maximum width of 1.074 mm.; an average length of 1.545 mm. 

 and an average width of 0.995 mm. The average length in 1912 was 

 1.465 mm. and the average width 0.974 mm. In 1913 the average 

 length was 1.64 mm. and the average width 1.02 mm., showing an 

 increase in size for the latter year of 0.175 mm. in length and 0.046 

 mm. in width. 



