THE GRAPE PHYLLOXERA IN CALIFORNIA. 



73 



phylloxerated vines, the rising temperature, and the intrinsic vigor 

 of the vine encouraging emigration. 



Apparently the young produced from the eggs deposited by over- 

 wintered females do not become wanderers, but those of later gen- 

 erations may, and many wandering larvae produced late in the au- 

 tumn settle on roots and hibernate. 



Wandering larvae play an important part in the diffusion of phyl- 

 loxera. 



THE NYMPH AND WINGED FORM. 



DEVELOPMENT. 



The individuals which are destined to become winged are termed 

 in their third instar " prenymphs " and in their fourth instar 

 "nymphs." They are produced from eggs deposited by adult radi- 

 cicoles, and until after their second molt differ in nowise from the 

 individuals destined to remain wingless; neither is there any dif- 

 ference in the eggs from which the two types hatch. In their third 

 instar the prenymphs (PL X, d, e, f) differ from the radicicoles of 

 that instar in that the former have more elongate and narrower bod- 

 ies and longer antennas and legs. The prenymphs are generally pale 

 greenish yellow, and their appendages appear quite dusky in com- 

 parison. Table XXIV gives measurements of four prenymphs. 



Table XXIV. — Measurements of prenymphs of the grape phylloxera, 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- 

 sorium. 



1 



2 



3 



1 



Mm. 

 0.805 



Mm. 

 0.405 



Mm. 

 0.357 



Mm. 



0.0948 

 .0939 

 .0946 



Mm. 



0. 0821 

 .0839 

 .0713 



Mm. 



0. 0330 

 .0321 

 .0306 

 .0306 



Mm. 



0.0268 

 .0277 

 .0279 

 .0279 



Mm. 



0.0839 

 .0889 

 .0973 

 .0919 



Mm. 

 0.0196 





.0193 



2 



.660 



.325 



.193 









3 



.541 

 .555 



.300 

 .284 



.186 









4 































i Individual 1, just before molting into nymph; individuals 2 to 4, very shortly after molting into pre- 

 nymphs. 



The prenymph molts into the nymph or pupa. The pupa is the 

 longest of all forms of the insect and is easily discernible on the 

 root by the presence of wing pads, even just after it has molted from 

 the prenymphal form, and has a greenish color. Immediately after 

 the skin is shed, these wing pads are yellow, but very quickly they 

 become gray or blackish. During the first few days of the nymphal 

 instar the insect is green or greenish yellow, and the compound eyes 

 are indiscernible, but as it grows it lengthens, becomes constricted in 

 the region of the metathorax, and turns orange, the mesothorax, how- 

 ever, remaining paler than the rest of the body. The compound 



