68 



BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



joint 1 wider than joint 2 ; third joint about twice as long as the two basal 

 combined and bearing a single oval sensorium near apex ; all three joints bearing 

 hairs. Beak pale, base and tip shining and dusky, reaching to second or third 

 abdominal tergite ; in specimens examined after they had transfixed the beak 

 into the roots, this organ appears to be shorter, due to the telescoping of the 

 sheath from the action of transfixing. 



Mesothorax largest segment of body, twice as long as prothorax, which is 

 next largest ; mesothorax divided into two sections by transverse fold. Thoracic 

 segments having median portions raised above lateral portions by means of 

 two longitudinal curved folds. Metathorax very similar above to any of first 

 five abdominal segments. Legs in pale specimens slightly darker than abdomen, 

 coxse dusky. 



Sixth abdominal segment produced conically at each of its posterior angles 

 and narrowed basally ; caudal segment twice as long as broad, bluntly rounded, 

 with a small central emargination and fringed with a marginal row of pale 

 weak hairs. 



The dorsum of the body bears six longitudinal rows of dusky circular tuber- 

 cular areas, which under magnification appear as thickenings and roughen- 

 ings of the epidermis, and each of these is surmounted by a single spine. 



Table XIX jnves measurements of the adult radicicole. 



Table XIX. 



-Measurement* of mature radicicole of the grape phylloxera, 

 Walnut Creek, Calif. 



Individual No. 



Length 

 of body. 



Maxi- 

 mum 

 width 

 of body. 



Length 

 of beak. 



Length 

 of hind 

 femur. 



Length 



of hind 



tibia. 



Length of antennal joints. 



Length 

 of sen- 

 sorium. 



1 



2 



3 



1 



Mm. 

 0.854 



Mm. 

 0.502 



Mm. 



Mm. 



0. 0795 

 .0804 

 .0839 

 .0875 



Mm. 



0. 0786 

 .0759 

 . 0748 

 .0768 



Mm. 



0. 0223 

 . 0252 

 .0260 

 .0197 



Mm. 



0. 0251 

 .0243 

 .0230 

 .0230 



Mm. 



0. 0661 

 .0660 

 .0673 

 .0705 



Mm. 

 0. 0224 







.0195 



2 



.87S 

 1.011 

 .997 

 .942 

 .783 

 .77S 

 .763 

 .734 

 .714 

 .712 

 .686 

 .631 

 .582 



.549 



.584 

 .558 

 .593 

 .507 

 .503 

 .455 

 .433 

 .448 

 .392 

 .408 

 .416 

 .352 



0.281 



.0196 



3 



.0205 



4 







5 

















6 

















7 

















8 

















9 

















10 

















11 

















12 

















13 

















14 

































Measurements of beaks from nine adult hibernants were made 

 March 18, 1915. Of these six, fixed in the root tissue, measured 0.27t5, 

 0.213, 0.260, 0.252, 0.198, and 0.179 mm., respectively. The other 

 three, not fixed since casting their last skin, measured 0.329, 0.317, 

 and 0.299 mm., respectively. The basal joints of the rostrum are 

 telescoped when the beak is thrust into the root. 



It is obvious from an inspection of Table XIX that the adult 

 radicicoles vary greatly in size. This variation occurs whatever kind 

 of food supply the phylloxeras are getting, although the average size 

 is larger on good succulent food than on that of poorer quality. Indi- 

 viduals 5 to 14 in Table XIX were all taken the same day (Mar. 18) 



