9 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE. 
almonds are attacked also. In Europe grape, peach, and nectarine 
are also attacked (Lowe). 
From the deciduous-fruit hosts mentioned the mealy plum aphis 
migrates in early summer to plants of the genera Phragmites, 
Typha, and Arundo, and in the late fall there is a return migration 
to the fruit trees. This is the normal process of migration. Occa- 
sionally the writer has seen generations of aphids persist on plum 
until September, a habit that Lowe (3) records as not unusual in 
New York State. The migratory forms are winged aphids and 
there are strong indications that they traverse long distances in pass- 
ing from host to host, as summer colonies have been found in June 
many miles from the nearest winter hosts. Vast numbers of migrants 
are produced both in spring and fall, and the production of consid- 
erable numbers of summer migrants serves to distribute the species 
among the summer hosts. In California Phragmites and Typha are 
the known alternate hosts. 
INJURY. 
In the early summer months the aphids occur on the foliage, often 
crowding together in great quantities. (Pl. I.) The lower surface of 
the leaf is the preferred location, but the petioles and upper surface 
are frequently infested. The young fruit is less commonly attacked. 
The infested leaves are generally curled and discolored and glisten 
with honeydew deposits. (Pl. II.) The ground beneath the tree is 
often sprinkled with the whitish shed skins dropped by the aphids. 
The combined effect of myriads of aphids feeding simultaneously on 
the tree produces fruit of small size and an early drop. In the years 
1915 and 1916 an unusual midsummer apical cracking of greem 
prunes developed in California. Morris (4), after making observa- 
tions in the Santa Clara Valley in 1915, opined that this cracking 
was due to aphis action. In 1916 the writer made some observations 
in Contra Costa County. He found that whereas on the whole crack- 
ing was more general on trees that previously in the season had been 
heavily infested with the aphis, it occurred also in other cases on trees 
which had escaped infestation. He could not conclude otherwise 
than that the aphis was not more than a contributing, or at least not 
the sole cause of the apical cracking in the prunes. 
1 Blakey (1), conducting his observations at Redditch, England, found no certain mi- 
gration from the winter hosts, the aphids remaining the year around on fruit trees. In 
this connection it is of interest to note that he found the active cycle (from hatching of 
stem mother to oviposition) to extend in HEngland from the beginning of May to the 
middle of October, 5.5 months, whereas in California the writer found the cycle to cover 
a period of 9 months (Mar. 1 to Noy. 30). The longer growing period enjoyed by the 
trees in California is of course responsible for this condition, and it is possible that the 
much dryer climate of California is concerned in the summer migration of the species to 
plants of a semiaquatic nature. ‘The writer has observed that the aphids tend to remain 
on the fruit trees later into the summer in the more humid than in the more arid 
localities of California, while the occurrence on May 15 of large colonies on a summer 
host at Salton Sea (a very arid region) suggested that the aphids were living on this 
host the year around. 
