WALNUT APHIDES IN CALIFORNIA. 9 



of examples remain immaculate throughout development. The 

 "lice" of the second generation develop more quickly than the stem- 

 mothers or first generation, owing to greater abundance of food 

 supply and to the higher temperature existing at that later period. 

 In 1911 second-generation young were deposited in the field on 

 early varieties of walnuts a little before April 23, while in the following 

 year these were deposited as early as April 6. This is to be expected, 

 since in 1912 the trees came out in leaf two weeks earlier than in the 

 previous year. Table II shows the life cycle of 41 individuals of the 

 second generation at San Jose, Cal., in 1911. 



Table II. — Life cycle of the second generation of Chromaphis juglandicola, San Jose, 



Cal, 1911. 



No. of 

 individ- 

 ual. 



Date of— 



Life 

 cycle. 



No. Of 

 individ- 

 ual. 



Date of — 



Life 

 cycle. 



Deposi- 

 tion. 



Acquiring 

 wings. 



Deposi- 

 tion. 



Acquiring 

 wings. 



1 



2 



3 



4 .... 



5 



6 .... 



7 



8 



9 



10 

 11 

 12 

 13 

 14 

 15 

 16 

 17 

 18 

 19 

 20 

 21 



Apr. 23 



23 



23 



23 



23 



24 



24 



24 



24 



24 



25 



26 



May 1 



1 



1 



1 



1 



2 



2 



2 



2 



May 12 

 12 

 14 

 16 

 18 

 18 

 18 

 18 

 18 

 18 

 20 

 21 

 21 

 21 

 21 

 21 

 21 

 21 

 21 

 22 

 22 



Days. 

 19 

 19 

 21 

 23 

 25 

 24 

 24 

 24 

 24 

 24 

 25 

 25 

 20 

 20 

 20 

 20 

 20 

 19 

 19 

 20 

 20 



22 



23 



24 



25 .... 



26 .. 



27 .... 



28 .... 

 29 



30 



31 



32 .... 



33 



34 



35 



36 .... 



37 



38 



39 



40 



41. 



May 2 

 2 

 3 

 3 

 3 

 3 

 3 

 4 

 4 

 5 

 5 

 5 

 6 

 6 

 6 

 6 

 6 

 7 

 8 

 9 



May 22 

 22 

 22 

 22 

 22 

 22 

 22 

 23 

 23 

 25 

 25 

 25 

 26 

 26 

 27 

 27 

 27 

 27 

 28 

 27 



Days. 

 20 

 20 

 19 

 19 

 19 

 19 

 19 

 19 

 19 

 20 

 20 

 20 

 20 

 20 

 21 

 21 

 21 

 20 

 20 

 18 



Life cycle : Days. 



Maximum 25 



Minimum 18 



Average 20. 7 



The aphides of the third generation appear on the earliest varieties 

 of walnuts about the middle of May, but on the late varieties such 

 as the Franquette this brood appears as much as a month later. The 

 individuals of this generation are on the average slightly larger than 

 those of other generations . In a large series of adult viviparous females 

 taken throughout the year of 191 1 the largest example was of the third 

 generation. Its body was 2.55 mm. in length and 1.06 mm. in width, 

 and both of its antennae measured 1.06 mm., or 0.02 mm. in excess 

 of the next longest antenna in the series. Table III indicates the life 

 cycle of 97 individuals of the third generation. 

 40859°— Bull. 100—14 2 



