38 



BULLETIN 351, TJ. S. DEPARTMENT OF AGRICULTURE. 



at 8.45 a. m . , at which time the larva resumed its migration . At 9.30 a. m. the temper- 

 ature was 80° F., at 10 a. m. 86° F., and at 11 a. m. 88° F., from which hour it dropped 

 to 84° F. at noon, when the experiment was terminated by the death of the larva. 



Ordinarily larvae start migrating when the temperature reaches 

 70° F., and the rate of travel increases in nearly the same ratio as the 

 increase in temperature above 70° F. Larv?e, if unattached, become 

 motionless when the temperature falls below 72° F. The female 



Fig. 12.— Tracing of the total twigward migration of a female larva of the terrapin scale. Reduced 8 times. 

 Total distance traveled, 322.5 cm. (Original.) 



under observation started migration August 30 at 2.40 p. m., and 

 died September 1 at 12 noon, having lived 2 hours and 40 minutes 

 less than 3 days, and having traveled over smooth paper a distance 

 of 322.5 cm. (10J feet). (Fig. 12.) This was undoubtedly farther than 

 the average specimen is able to travel upon its host plant. Titer e is 

 therefore very little chance of the larvae, crawling to adjacent trees unless 

 the limbs are in contact. 



A second female larva (Table XXV), captured August 26, during 

 the first day of migration, was placed upon wrapping paper at 2.25 



