24 BULLETIN 351^ U. S. DEPARTMENT OF xVGRICULTUEE. 



Size of the Larv.e at Time of Migration. 



The size of the larvse varies. Strong females produce larger 

 young than weak ones. The larvae are largest at the beginning of 

 reproduction. They gradually become smaller as the season ajivances. 

 Measurements made in June, 1913, of 10 larvae give the following 

 results: Length, maximum 0.475 m.m., minimum 0.41 mm., average 

 44 mm.; wddth, maximum 0.26 mm., minimum 0.20 mm., average 

 0.23 mm. 



Description op the Migrating Larvae. 



The distinguishing characteristics of the leaf migrant are: Average 

 length, 0.43 mm.; average width, 0.23 mm.; color, pale translucent 

 yellow, with reddish brown eye-spots; body very flat and oblong; 

 antennae with six joints; feeding tube internal and folded midway 

 upon itself. (PI. I, fig. 2, p. 8.) The anal plates have each a single 

 major apical seta 0.2 mm. in length. The plates have their distal 

 ends just reaching to the tips of the body lobes. These plates, are 

 held m a relaxed position, that is, with then" adjacent edges forming 

 an acute angle. The terminal anal plates, together with the folded 

 feeding tube, are reliable characters for identifying the leafward 

 migrant. 



LEAF-ATTACHED LARV.'E. FIRST INSTAR. 



The larvae emerge, make their migration, and attach to the leaves 

 during the second day after birth, but take no food until after attach- 

 ing to the leaf. Death by starvation and exhaustion results during 

 the third day after emerging provided an attachment is not made. 

 It is doubtful whether the laiwae can live m the brood chamber more 

 than 4 or 5 days, and at any rate they would be too weak after the 

 fourth day to make an effectual effort to reach the leaves. In 1912 

 there were several periods in which it was cool and wet for four 

 successive days. After these periods many dead larvae were found 

 in the brood chambers, some chambers becoming so clogged as to 

 prevent the further escape of young. 



The larva, after attaching to the underside of the leaf, retains in 

 the main its earlier characteristics. The proboscis is thrust into the 

 leaf tissues. The anal plates, which during the migration were car- 

 ried with their adj acent edges diverging, are now held in close contact 

 when in repose. The body lobes, which at attachment were even 

 with the tips of the anal plates, grow steadily backward and inward 

 until they meet behind the anal plates. By this growth the anal 

 plates with their long setae are made to recede from the posterior edge 

 to a position upon the dorsal surface, as shown in Plate I, figure 3, a, h, 

 p. 8. A thin, brittle covering of wax appears on the dorsal surface of 

 the larvae during the latter part of the first instar. All leaf-attached 



