110 MISCELLANEOUS STUDIES 



and a third generation is begun. The most usual place to find the 

 second and third generations is in the curled terminal leaves of the 

 plant. These leaves are curled very similarly to those by the green 

 apple aphis (Aphis pomi De Geer), but they are curled a great deal 

 tighter. Winged females may appear in this third generation, but 

 it is most usual to find them in the fourth. Horticultural Commis- 

 sioner Volck of Santa Cruz County states that he has counted four 

 generations before the summer migration. During May, 1915, the 

 author collected many colonies of this Aphis and placed them in vials 

 in the laboratory. Many others he attempted to colonize on some 

 apple seedlings. Owing to various causes he was unable to make any 

 successful colonizations on the apple trees, one of the chief causes 

 being the destructive work of coccinellid larvae. Also during the 

 first few days of June he was forced to be absent from town and on 

 his return found that the gardener had "cleaned" the trees, for 

 "they were all covered with lice." Until May 25 no alate females 

 had been found, but on that date two appeared in the laboratory. On 

 May 10, 1917, alates were found in Orange County. 



These alate females of the fourth (perhaps sometimes they appear 

 in the third) generation migrate from the apple to some unknown 

 host. At Stanford University in 1915 the migration began about 

 the first of June and continued for some two or three weeks. On 

 June 20 only two or three colonies, each consisting of but a very few 

 individuals, were found where a month before there had been literally 

 hundreds. The curled leaves still hung on the trees and in each 

 curled leaf the moulted skins of the aphid were abundant. From 

 Commissioner Norton of Nevada County comes the statement that he 

 has known the migrants "to leave the trees as early as the middle 

 of June, but the migration usually takes place between the first and 

 the fifteenth of July. "Where they go I have never been able to find 

 out, as I have never observed them on any other host plant. ' ' 



According to O. E. Bremner, Horticultural Commissioner of 

 Sonoma County, the migration takes place there during June. This 

 is the same as in Santa Clara County. In Orange County in 1917 

 the alate females appeared about the first of May. Migration began 

 almost immediately and continued for two or three weeks. By May 24 

 only a very few aphids remained. This is fully a month earlier than 

 migration takes place north of the Tehachapi. Incidentally the spring 

 of 1917 was exceedingly cool and the summer very late. In normal 

 years one would expect the aphids to leave the apple two or three 

 weeks earlier. 



