THE GRAPE PHYLLOXERA IN CALIFORNIA. 



125 



are lemon yellow and oval. Upon hatching from the egg, the bright- 

 yellow larva seeks food. Larva? hatching in spring mostly settle near 

 the eggshells, but in summer and autumn a considerable percentage 

 travel along the roots or forsake the vine altogether, either following 

 cracks in the soil to reach neighboring vines or ascending to the sur- 

 face of the soil and traversing the ground in their endeavors to reach 

 other vines. To those that voluntarily forsake the vine has been 

 given the term " wanderers." The larva? molt four times, and on the 



Fig. 10. — Diagram to illustrate annual life history : Innermost shaded crescent, active 

 period of wandering radicicole larva? ; middle shaded crescent, period of development 

 of the sexuparous migrant ; shaded portion of outer circle, hibernation period of 

 radicicole larvse ; unshaded portion of outer circle, period of active life on the roots. 



completion of the final molt become mature insects. At first oval, 

 they tend to become pyriform as they grow. The color, yellow, 

 yellowish-green, or yellowish-brown, is dependent on the nature of 

 the food. The length of the developmental period varies according 

 to food and meteorological conditions. On succulent living roots 

 the average period of larval development was found to be about 22 

 days (hibernant generation excluded), and the maximum and mini- 

 mum respectively 36 and 10 days. 



