THE GRAPE PHYLLOXERA IN CALIFORNIA. 



51 



single lots containing individuals incubating under the same average 

 temperatures but belonging to more than one year have been com- 

 bined. 



Table IX. — Incubation of the eggs of the grape phylloxera on living roots, 

 Walnut Creek, Calif., 1913-1915. 



Lot number. 



Number 

 of eggs. 



Average 

 tempera- 

 ture. 



Incuba- 

 tion. 



Months or month. 



1 



19 

 11 

 11 



( 2 ) 



7 



6 

 ( 2 ) 



28 

 ( 2 ) 



3 

 11 

 23 

 26 

 21 

 11 

 45 

 23 



8 



o p 



56.8 



57 



58 



58.5 



60 



61.8 



62 



63 



64 



66 



68 



69 



70.5 



71.5 



72 



72.5 



73 



73.2 



Days. 



U9.0 



15.1 



14.8 



15.0 



12.3 



11.2 



9.0 



9.0 



9.7 



3 9.5 



10.5 



3 8.2 



3 7.7 



9.4 



8.4 



3 7.7 



3 7.0 



3 6.4 





2 , 



3 



April. 



April to May. 

 Do. 



4 



5 



Do. 



6 



May to June. 

 Do. 



7 



8 



Do. 



9 





10 



Do. 



11 





12 





13 





14 



Do. 



15 



August. 



July to September. 

 Do. 



16 



17 



18 



July. 





1 Maximum, 20 days. 



2 About 20. 



3 Minimum, 6 days. 



Many of the lots contained a very small number of individuals, 

 but in the main the incubation stage became progressively shorter 

 as the average temperature rose. Between the temperatures of 56.8° 

 and 62° F. the incubation periods are rapidly reduced, while between 

 62° and 73.2° the reduction is much less rapid in proportion to the 

 rise in temperature. This is a somewhat similar condition to that 

 found in the cellar records. 



It is evident that the stage was shortest during the months of July 

 and August, and longest during the months of March and April. 

 Records began as early in the year as March 31, and closed as late 

 as October 5. Two of the individuals in lot 1 incubated in the maxi- 

 mum period of 20 days (Mar. 31 to Apr. 20) under an average tem- 

 perature daily of 56.8° F. The minimum of six days was reached 

 by 17 individuals in each of the months from June to September 

 under average daily temperatures of from 66° to 73.2° F. 



The condition of food had no apparent effect upon the duration 

 of the egg stage. Eggs deposited by radicicoles which had developed 

 from eggs deposited by gallicoles received from Virginia incubated 

 in the same average period as those descended from radicicoles of 

 many generations, and eggs deposited by nymphicals incubated pre- 

 cisely as did those laid by normal radicicoles. Individual incubation 

 records, both of eggs reared in the laboratory cellar and of others 

 reared on living vines, are given in connection with the development 

 of the radicicoles under the same conditions in the section on " De- 

 velopment of the radicicole larva," pages 54, 55, 57, 60-62, and 63. 



