1920] 



Patch: Aphids and Coccids 



161 



indicated by the circumstance that the best defined examples 

 of migration are exhibited by gregarious species and is corre- 

 lated with the exhaustion by the aphids of the infested food- 

 plant in the spring and with either that or a normal ripening of 

 the food-plant in the fall. The evidence of Shinji, based upon 

 food tests under chemical control appear to be of especial 

 significance in this respect. 



V. PHYLLOXERIN^.* Life Cycle Typical for the Phylloxerans. 



I. Stem-mother (apterous female; hatching from the 

 overwintering egg; causing the gall on 

 hickory and developing within it; laying 

 eggs that develop parthenogenetically). 



II. 



alate female (developing in gall; 

 laying a number of eggs 

 on hickory that develop 

 parthenogenetically to 

 males). 



III. male (apterous, dwarfed, 

 beakless). 



II. alate female (developing in gall 

 laying a number 

 of eggs on hick- 

 ory that develop 

 parthenogenet- 

 ically to sexual 

 females). 



III. sexual female (apterous, dwarfed, 

 beakless; laying 

 a single fertilized 

 egg). 



I. winter egg (on branch of hickory). 

 No longer included with the Family Aphididse in its restricted sense. 



Although the testimony of aphids in the North emphasizes 

 the annual occurrence of the fertilized egg, the parthenogenetic 

 reproduction, which is characteristic for all but a single annual 

 generation, may in many species be indefinitely continued in a 

 warm climate or in hot house conditions (as witness Ewing's 87 

 generations with Aphis avencB). Whether temperature is the 

 direct control in such cases may be doubted for we have many 

 species producing both alate and apterous forms throughout the 

 summer; and it may be that the continual vegetable growth 

 made possible by the warm climate is the direct encouragement 

 to parthenogenetic viviparous reproduction. This supposition 

 is accentuated by the fact that even in tropical climates experi- 

 encing a wet and a dry season gamogenetic eggs are produced to 



