THE TEEBAPIX SCALE. 



19 



LEAFWARD MIGRATION. 



The migration to the leaves begins immediately after emergence. 

 The larvae start emerging usually about 10 a. m., or even earlier if 

 the temperature is high, and by 3 p. m. the daily migration has 

 nearly ceased. At Mont Alto, Pa., during the noon hours of June 15 

 to 20, the branches of infested trees were swarming with countless 

 numbers of migrating larvae. During the leafward migration the 

 larvae are strongly phototropic and negatively geotropic. The time 

 required for an individual to make this mi- 

 gration and to take its position upon the 

 leaf is remarkably short. 



Two hours is about the average time from 

 emergence to the completion of the migra- 

 tion. Many reach the leaves and attach in 

 less than an hour, but others, especially those 

 that have ascended dead branches, may con- 

 tinue to move about for several days if a 

 suitable leaf is not found sooner. 



It is very unusual for the larvae to relocate 

 when they have once taken position upon a 

 leaf, though they do this when the leaf loses 

 its vigor. The larvae, except in rare and 

 unusual cases, attach to the underside of the 

 leaves, mostly alongside and parallel to the 

 midrib, or the larger veins. (Fig. 5.) 



Larvae usually attach to the first avail- 

 able leaves. The basal leaves upon an 

 infested branch are always more heavily 

 infested than those farther up. A sticky 

 secretion upon the very young leaves repels 

 the young larvae and prevents them from 

 attaching. The wooly coat of the fruit pro- 

 tects it from larvae. Larvae frequently crowd 

 upon the fruit, but in their struggles to free themselves from the fuzz 

 they invariably fall to the ground. 



The rate of migration varies with the temperature and the surface 

 upon which the larvae are placed. Table XIII gives the rate per 

 hour, time, temperature, and the distance traveled by five migrating 

 larvae of the first instar upon smoked wrapping paper. The average 

 temperature in this experiment was very favorable, being 87° F. 

 The rate per hour was very low, owing to the annoyance caused 



Fig. 5. — Peach leaf with attached 

 larvae of the terrapin scale. 

 (Original.) 



