120 MISCELLANEOUS STUDIES 



spring and begin attacking the tender leaflets, shoots and suckers, usually those 

 at the base of the tree or nearest the ground. These first plant lice are all wing- 

 less. As soon as the buds, young fruit, and leaves appear they are promptly 

 attacked, the entire crop often being entirely ruined. The leaves are curled and 

 weakened, while the young fruit is so distorted as to be killed or rendered unfit 

 for market. During the months of April and May winged migratory females 

 appear, which start colonies on other trees. The work continues until about the 

 middle of July, when most of the lice leave the tops and again go to the roots. 



139. Aphis pomi De Geer 

 Figures 225 to 227 



De Geer, Memoires, vol. 3, p. 173, 1773 (orig. desc.). 



Davidson, Jour. Econ. Ent., vol. 2, p. 301, 1909 (list). 



Davidson, Jour. Econ. Ent., vol. 3, p. 377, 1911 (list). Aphis mali Fabr. 



Weatherby, Mon. Bull. Cal. Comm. Hort., vol. 1, p. 318, 1912 (list). 



Games, Mon. Bull. Cal. Comin. Hort., vol. 1, p. 399, 1912 (list). 



Branigan, Mon. Bull. Cal. Comm. Hort., vol. 4, p. 285, 1915 (list). 



Hurdley, Mon. Bull. Cal. Comm. Hort., vol. 4, p. 445, 1915 (list). 



Baker and Turner, Jour. Agr. Res., vol. 5, pp. 955-995, 1916 (complete 



account). 



Eecords. Pyrus mains; Crataegus oxycantha; Catalpa sp. ; California. 



In California this species has been reported on apple and haw- 

 thorn (Crataegus sp.) at Stanford University by Davidson and 

 Morrison; in Humboldt County by Weatherby; at Santa Rosa by 

 Games; and by others in Orange, Placer, Sonoma, Santa Cruz, San 

 Bernardino, and Monterey counties. Horticultural Commissioner 

 Armitage states that it has never been found in San Diego County, 

 and Horticultural Commissioner Norton writes that it is unknown in 

 Nevada County. These are the only two of the apple growing regions 

 of the state in which it is not known. The author has found it at 

 Stanford University on apple, catalpa, pear, and hawthorn, and at 

 Marysville on catalpa. Gillette lists loquat, quince, and flowering 

 crab as additional hosts. It seems to prefer the apple to other hosts, 

 and it is on the apple that its greatest injury is done. Gillette states : 

 ' ' Among the apple trees it has its preference. Missouri Pippin seems 

 to be its first choice, while Rome Beauty, Black Twig, Ben Davis, and 

 a few others are second choice, and the Northern Spy is scarcely 

 attacked." The fact that the Northern Spy is almost immune is 

 interesting in that this variety is also quite immune to the devastations 

 of the woolly aphis (Eriosoma lanigera Hausman). 



The life history of this aphid is quite similar to that of many other 

 species, and is as follows : 



