THE GRAPE PHYLLOXERA IIST CALIFORNIA. 31 



RESUME OF LIFE HISTORY IN CALIFORNIA. 



A resume of the life history will be presented before all the dif- 

 ferent stages and habits of the phylloxera in California are discussed 

 in detail. This resume is confined to the biology of the insect on 

 viniferse and does not consider the life history on resistant roots. 



Over 99 per cent of the phylloxeras pass the Avinter as small brown- 

 ish unmolted larvse, the remainder hibernating after having passed 

 one or two molts. All parts of the root system are used for hibernat- 

 ing quarters, but the majority cluster on the larger roots, following 

 an upward migration in the fall. 



Coincident with the first sap flow in early spring is the growth of 

 the hibernants, but in a given vineyard the earliest individuals com- 

 mence to grow fully six weeks before the most tardy ones, so that 

 after the foliage has opened, hibernating larvae are still to be found 

 on the roots. The development of the hibernants is considerably 

 slower than that of the summer broods, and the former mature on 

 the average about five and one-half weeks after they commence their 

 spring growth. The development of the larvse is at all times influ- 

 enced by the quality of food and by conditions of humidity and 

 temperature. 



Upon casting its fourth skin, the hibernant is mature and com- 

 mences egg deposition. Its progeny are the first-generation phyl- 

 loxeras, and these on hatching from the eggs either settle beside the 

 eggshell or go in search of new food. Many aphids settle on young 

 growing rootlets and produce the fleshy swellings, termed " nodo- 

 sities." Others settle upon older roots and produce swellings, termed 

 "tuberosities." Still others develop on roots without causing the 

 development of either perceptible swellings or lesions. Individuals 

 feeding upon nodosities develop more rapidly than do those on the 

 unswollen surface of the root. The nodosities usually decay within 

 a few weeks after their formation, and in most cases the destruction 

 of the rootlets follows. The tuberosities also usually decay in time. 

 The rotting of the nodosities is not very serious, as the vine can 

 supply new apical growth, but the decay of the tuberosities leads to 

 the decay of the larger roots either wholly or in part, and as a result 

 the vitality of the vine is greatly impaired, or the vine is killed 

 outright. 



The first-generation individuals are mature in from four to seven 

 weeks after the eggs have been deposited, and they in their turn 

 deposit eggs, which produce further generations throughout the 

 summer and autumn. 



Owing to the fact that, under favorable conditions, the adults 

 deposit eggs during an average period of 45 days, an overlapping of 

 generations ensues during the summer and fall. In order to avoid 



