THE GRAPE PHYLLOXERA IIST CALIFORNIA. 



47 



period of egg deposition, the aphids often change their orientation 

 by pivoting about the beak. 



Time of day of oviposition,. — Between April 28 and May 25, 1913, 

 records were taken in the cellar to obtain data upon the time of day 

 of oviposition. The maximum daily temperature occurred about 

 6 p. m., 9 and the minimum about 7.30 a. m. Between 9 a. m. and 

 5 p. m. (8 hours), 41 eggs were deposited, and between 5 p. m. and 

 9 a. m. (16 hours), 52 eggs were deposited in the 27 days. Between 

 9 a. m. and 5 p. m., there was an average hourly temperature in 

 excess of that occurring between 5 p. m, and 9 a. m. of about 0.02° F. 

 It is apparent that the higher temperature of the shorter period 

 caused a comparatively greater number of eggs to be deposited, 

 since the 52 eggs were laid in exactly double the time in which the 

 41 were deposited. 



Egg fertility and mortality. — A large series of experiments took 

 place in 1911 to determine the fertility and mortality percentages of 

 the eggs of the radicicole phylloxera. These were carried on about 

 evenly throughout the year. One series was conducted under cellar 

 conditions in petri dishes, and the other took place in the laboratory 

 under a higher temperature and was exposed to subdued daylight. 

 Table IV gives the results of these experiments : 



Table IV. — Fertility and mortality of the radicicole egg of the grape phylloxera, 

 Walnut Creek, Calif., 1911. 



Generation and environment. 



Total 

 number of 



eggs 

 deposited. 



Number of 



eggs 



hatched. 



Number of 



eggs that 



failed 

 to hatch. 



Percentage 

 hatched. 





965 



772 



193 



80.00 







1 (Cellar) 



1,000 

 490 



911 

 422 



89 

 68 



91.10 





86.12 







1 (Total) 



1,490 



1,333 



157 



89.52 







2 (Cellar) 



1,840 

 245 



1,716 

 236 



124 

 9 



93.26 





96.33 







2 (Total) 



2,085 



1,952 



133 



93.62 







3 (Cellar) 



1,112 



524 



987 

 486 



125 

 38 



88.76 





92.75 









6,176 



5,530 



646 



89.54 







There was no appreciable difference between the fertility of 

 those reared in the cellar and of those reared in the higher tempera- 

 tures of the laboratory rooms. The results indicate that on the aver- 

 age almost 9 eggs out of every 10 laid will hatch. It \z probable that 

 vineyard conditions produced similar averages as no predators or 

 other causes that might bring about a different average have been ob- 

 served with the exception of the case of excessive spring moisture 

 acting upon the eggs laid by the overwintered adults and in the case 



9 All references to clock time refer to " Standard time." 



