76 



BULLETIN 903, U. S. DEPARTMENT OF AGPdCULTURE. 



Table XXVI. — Measurements of the icinged migrant of the grape phylloxera, 



Walnut Creek, Calif. 





1 



2 



3 



4 



5 



6 



7 



8 





Mm. 



1.101 

 -.428 

 .333 



Mm. 



Mm. 



Mm. 



Mm. 



0.906 

 .317 

 .309 



.0320 

 .0366 

 .1741 



.0536 



.0214 



.0250 



.1848 

 .2062 

 .229 



Mm. 



Mm. 



Mm. 

 0.900 



Width (abd. sez. 3) 













.390 



Width (thorax). . 















Antennal joints, length: 



1 



0. 0384 

 .0402 

 .1902 



. 0562 



.0268 



.0286 

 .1901 

 .2179 



0. 0375 

 . 0393 

 .1809 



" .0034 



.0304 



.0269 

 .1802 

 .2250 



0. 0321 

 .0304 

 .1777 



.0241 



.1500 

 .1643 



0. 0393 

 .0384 

 .1946 



.0589 



.0304 



.0277 







2 





0.063 

 .0275 

 .0297 



.033 



3 





.207 



Antennal joint 3, base to apex of basal 







Antennal j oint 3, length of basal sen- 







Antennal j oint 3, length of apical sen- 













Hind tibia, length 





















Wing expanse 













2.73 





















The prenymphal instar is passed in three or four clays, in the same 

 time in which the corresponding instar of the wingless radicicole is 

 passed. The nymphal instar, however, is relatively longer than the 

 corresponding instar in the wingless form, and it is because of this 

 fact that the migrant takes longer to mature than does the contempo- 

 raneous wingless radicicole. The nymphal or pupal instar occupies 

 from 5 to 12 days, the average being about 8 days. 



The nymphs take more food than does the corresponding wingless 

 form, and after they have left a nodosity or tuberosity upon which 

 they have been feeding, the lesion rapidly decays unless other in- 

 dividuals are settled upon it. The nymphs do not usually move 

 much during their period of growth, but if disturbed they move 

 quickly and display a negative phototropism when suddenly exposed 

 to light. The newly molted nymphs, however, often wander about 

 with apparent aimlessness. The full-grown nymphs just before 

 molting ascend the roots, seeking the surface, and transform on the 

 trunk or else find their way along the root until they come to a crack 

 in the soil, and crawling up the sides of the crack transform near the 

 surface. In glass sections cages, wherein the glass plates did not fit 

 very tightly to the soil, the nymphs were found sometimes crawling 

 up to within 2 or 3 inches of the surface and sometimes transforming 

 close by the roots as much as 17 inches below the soil surface, the 

 resultant winged aphids being compelled to find their way to the 

 surface. It was concluded that owing to the loosely fitted glass 

 plates of the section cages, which allowed abnormal light to penetrate 

 below the surface of the soil, the nymphs did not wait to ascend to- 

 ward the surface, but transformed below, their transformation being 

 governed by the strength of the light rays to which they were sub- 

 jected. It may be said that these section cages measured 9 by 24 

 inches, outside measurement, and allowed of a thickness of half an 



