October, '21] lathrop: apple aphids 439 



The wingless \'i\dparous females were produced throughout the summer 

 and were present until killed by frost in late November. So far as 

 could be determined, there was no tendency to produce oviparous forms 

 in the fall, and there was no indication that the species could maintain 

 its existence upon apple for more than one season without the aid of the 

 plantain forms. 



Aphis pomi also shows a regional difference in the production of winged 

 fonns. Baker and Turner found that "in the second generation, the 

 winged form outnumbers the wingless" in Virginia. During the spring 

 of 1916, the writer observed colonies at Geneva, N. Y. in which at least 

 ninety per cent of the second generation developed wings. This high 

 percentage of winged forms in the second generation seems characteristic 

 of A. pomi under Eastern climatic conditions. The scarcity of winged 

 forms of later generations is equally characteristic. 



Observations in Western Oregon show that there is much less tendency 

 to thus segregate the development of winged forms. In this section, 

 winged forms are usually not numerous in the second generation. Here 

 the migrator}' forms are much more numerous in the later generations 

 than is the case in the East. 



Winter Activities 



The hibernation of Aphis pomi as observed in Oregon shows no con- 

 spicuous variation from the behavior of the species elsewhere. 



Aphis avenae in Western Oregon winters principally as viviparous 

 fem.ales on grains and grasses, where growth and reproduction take place 

 during the winter months when the temperature permits. Compara- 

 tively few migrants appear on the apple in the fall and hibernation in the 

 egg stage on apple is uncommon. 



Aphis sorbi in Western Oregon produces numerous migrants which 

 return to the apple in the fall, and are nonnally sufficient to produce a 

 severe infestation. However, in this section, only a portion of the plan- 

 tain forms become winged in the fall. A considerable percentage remain 

 on plantain throughout the winter months. Reproduction and growth 

 continue dtuing the winter, although reduced to a verj^ low rate. Speci- 

 mens bom in the insectary at Corvallis, November 27, matured February 

 10- — a developmental period of seventy-four days. 



Wintering on plantain is apparently normal with this species in the 

 climate of the Willamette Valley, for infestation has been observ'cd in the 

 field throughout every winter since 1917. During the winter of 1919-20, 

 Aphis sorbi on plantain in the field, where protected by snow, withstood a 

 temperature of thirteen degrees below zero. Where there is no pro- 



