THE TEBEAPIN SCALE. 



29 



development of the female. 



Female Larva, Second Instar. 



During the second instar the females increase in length from an 

 average of 1 mm. to an average of 1.6 mm., and in width from an 

 average of 0.525 mm. to 1 mm., but there is very little increase in 

 height. 



Table XXI shows the average measurements of 268 females taken 

 at frequent intervals during this instar. These females emerged 

 from June 20 to 26, 1913; that is, during the height of the emergence 

 period. 



Table XXI. — Measurements of 268 female terrapin-scale larvae of specified ages during 

 the second instar , Mont Alto, Pa., 1913. 



No. 



Emerged. 



No. of 

 speci- 

 mens. 



Average 

 age at 

 time of 

 entering 

 the sec- 

 ond 

 instar. 



Age when 

 meas- 

 ured. 



Days in 

 second 

 instar. 



Average 

 length. 



Average 

 width. 



1 



1913. 

 June 26 

 ...do 



20 

 39 

 17 

 30 

 21 

 19. 

 16 

 7 



17 

 21 

 16 

 20 

 11 

 14 



Bays. 

 19 

 19 

 21 

 19 

 19 

 22 

 22 

 22 

 22 

 22 

 19 

 22 

 22 

 22 



Bays. 

 20 

 21 

 22 

 23 

 24 

 26 

 27 

 30 

 30 

 31 

 32 

 33 

 34 

 36 



1 



2 



1 



4 



5 



4 



5 



8 



8 



9 



13 



11 



12 



14 



Mm. 

 1.054 

 1.076 

 1.063 

 1.114 

 1.257 

 1.431 

 1.380 

 1.471 

 1.395 

 1.504 

 1.506 

 1.587 

 1.575 

 1.483 



Mm. 



0.558 



2 



.590 



3 



June 24 

 June 26 

 ...do 



.55 



4 , 



.638 



5 



.676 



6 -. 



June 24 

 ...do 



.775 



7 



.776 



8 



...do 



.892 



9 



June 21 

 June 20 

 June 26 

 June 24 

 ...do... 



.713 



10 



.835 



11 



.937 



12 



.978 



13.. 



1.012 



14 



...do 



.966 



Total ; .. 





268 



























The rate of growth is very uniform throughout the second instar, 

 but there is a variation in size among specimens of the same age. 

 This is instanced in lines 8 and 9. Such variations are common and 

 are usually the result of weather conditions or of low vitality in the 

 host. In this instar there is very little growth in height, the aver- 

 age height at the end of the instar being about 0.11 mm. There is 

 no change in color. The excretion of honeydew is moderate and is 

 unimportant. The female has but slight ability to change position 

 and seldom moves from one position to another upon the leaf. 

 Larvae from withering leaves, when placed upon fresh ones, mostly 

 fail to make a satisfactory attachment. 



In an experiment, twigs, the leaves of which were infested with 

 second-instar larva?, were placed in water. The larvae soon loosened 

 and migrated to the twigs. The advanced specimens made the sec- 

 ond molt prematurely and migrated in the third instar; the young 

 specimens, even those less than half the normal size, migrated also, 

 but without molting. Some of the smaller specimens would un- 

 doubtedly have reattached to fresh leaf tissue had there been any 

 on the twigs. The others attached in the normal manner to twigs. 



