THE GRAPE PHYLLOXERA IN CALIFORNIA. 



67 



Table XVIII. — Measurements of fourtlv-instar radicicoles of the grape phyl- 

 loxera, Walnut Creek, Calif. 



Individual No. 1 



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- 



soriuru. 



1 



2 



3 



1 



Mm. 

 0.919 

 .851 



.824 

 .615 



Mm. 



0.517 

 .528 

 .579 

 .500 



Mm. 



Mm. 

 0.0848 



Mm. 

 0. 0687 



Mm. 



0. 0321 

 .0321 

 .0276 

 . 0306 

 .0297 



Mm. 

 0. 0259 

 .0277 

 .0241 

 .0261 

 .0248 



Mm. 



0. 0669 

 .0571 

 .0768 

 .0748 

 .0721 



Mm. 



2 







3... . 





.0830 



.0749 



0. 0212 



4 



0.172 

 .162 

 .160 



.0167 



5... . 







.0162 



6... 



.753 



.700 



.426 



.0802 



.0671" 





72 





























1 Individuals 1-3 were measured toward the end of the instar, and individuals 4-7 very shortly after 

 molting. 



2 Maximum height, 0.3 mm. 



A very obvious growth takes place during the fourth instar (PL X, 

 ff-j). At the end of this instar the phylloxera casts its last skin 

 and issues therefrom as an adult. The adults, except immediately 

 following the molt, are never as pale as the immature forms. They 

 may be distinguished from fourth-instar individuals by two longi- 

 tudinal furrows on the thorax and by the relatively larger dorsal 

 tubercular areas. The color varies from a light green to a dark 

 purplish brown in living specimens. This variation is to a great 

 degree dependent on the food supply. On fresh, fleshy nodosities 

 the insects mostly are pale green with the tubercular areas very 

 noticeable. On tuberosities, or on the normal surface of a vigorous 

 root, the color is yellowish green, olive green, or light brown, with 

 the tubercular areas often less evident. 



On roots of poor quality the adults are brown or orange and the 

 tubercular areas hardly perceptible to the naked eye. After weeks 

 of egg production old adults become brown or purplish brown. In 

 shape the adults while not engaged in egg laying are hemispherical 

 or short oval, about equally rounded at either extremity, but while an 

 egg is being passed the insect assumes a pyriform shape and the 

 caudal end is much tapered and extended. 



Mature radicicole. 

 PI. IX, a, b, c. 



Color varying from pale green and pale yellow to deep purplish brown, de- 

 pendent on character of food and age of individual ; shape hemispherical, 

 short oval, pyriform while passing the ova; body obscurely glabrous, often 

 appearing to be coated on the dorsum with a very fine whitish powder; under 

 side of abdomen paler than upper. Body about twice as long as wide, widest 

 at middle of mesothorax ; highest at about cephalic third ; body flattening both 

 cephalad and caudad from this point. Head with dusky central area; eyes 

 dark red, each composed of three circular facets, arranged in form of an equi- 

 lateral triangle; antennae pale, not quite reaching posterior margin of head, 

 composed of three joints, of which the two basal are subequal in length but 



