A SYNOPSIS OF THE APHIDIDAE 109 



This is one of the most injurious of our California species of Aphis, 

 being found in practically all of the apple-growing regions of the 

 state, and in most of them necessitating some control measures. It 

 has been reported on apple and pear in the following counties : Hum- 

 boldt, Orange, Placer, Sacramento, Santa Clara, Shasta, Tehama, 

 Nevada, Inyo, Santa Cruz, and Alameda. Probably it is present 

 wherever apples are grown, with the exception of the southern Cali- 

 fornia districts where it has never been observed. The apple is the 

 primary host, and only occasionally has it been taken on pear. In 

 May, 1917, Roy K. Bishop found it in Orange County, this being the 

 first report of it south of the Tehachapi. 



The life history of this Aphis in California is as follows : 

 In the fall and early winter the eggs are laid in the crotches of the 

 twigs. These hatch in the following spring, the exact time depending 

 upon the weather conditions but it is usually as the buds are begin- 

 ning to show green, or as they are beginning to open. The author has 

 observed the young stem mothers on the young buds of the apple in 

 the latter part of March, although he has never been able to find the 

 eggs, either those yet unhatched or those from which the stem mothers 

 have already hatched. Horticultural Commissioner Weatherby of 

 Humboldt County writes that he has found the eggs hatching as early 

 as February 24. He goes on to state that the eggs of Aphis pomi 

 De Geer do not hatch until considerably later. Horticultural Com- 

 missioner Norton of Nevada County has made the following observa- 

 tions : 



The eggs of Aphis sorbi [malifoliae] are laid on the buds, or sometimes on 

 the spurs close to the buds. At first they are hard to see as they are small and 

 light green, but later they turn to a shiny black, when they can be more readily 

 detected. The young aphids hatch as soon as the buds begin to swell, which time 

 varies with the season. I have found them sometimes as early as the first of 

 March and at other times as late as the middle of April. 



The stem mothers feed upon the plant juices through the buds, 

 sometimes appearing on the outer surface of the buds and at other 

 times crawling down into the unfolding leaves, as is the case with 

 Aphis pomi De Geer. In a few weeks these are mature and begin to 

 deposit live young. All of this second generation are apterous females 

 so far as the author has been able to observe. On April 12, 1915, he 

 found several colonies of these aphids in the apple orchard at Stanford 

 University, each colony consisting of a stem mother and several young 

 apterous viviparous females. These females mature in a few weeks 



