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JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 11 
Schrank) alternating between hop and plum, two plants widely sep¬ 
arated botanically, or the Black Cherry Aphis ( Myzus cerasi Fabr.) 
migrating back and forward between cherry and Lepidium, a small 
cruciferous plant. Again the summer forms of the Spinach Aphis 
(Myzus persicoe Sulz.) are equally at home on lettuce, a composite, on 
turnip, a crucifer, or on parsley, an umbellifer. Similarly the Bean 
Aphis ( Aphis rumicis L.) feeds in summer upon leguminous and Cheno- 
podiaceous plants alike. 
In many of the species complications exist by reason of the fact that 
the insects may live the year around on the summer host or hosts. 
The root-inhabiting species all have this habit: the Beet Aphis 
(Pemphigus betoe Doane) normally winters on Populus but colonies 
may occur on beet or other roots any time of the year, and similarly 
the woolly aphids of apple and pear ( Eriosoma lanigerum Haus. and 
E. pyricola B. & D.) pass the winter in a dormant state on elms and 
in an active state on apple and pear, the normal summer hosts respec¬ 
tively. It might here be observed that in California, at least in locali¬ 
ties where both the apple and pear woolly aphids abound, the spring 
forms of the pear insect are very commonly marked on elms whereas 
these forms of the apple species are quite rare on the winter host. 
In the southern and southwestern portions of the United States the 
semi-tropic climate is mild enough to allow aphids to feed and repro¬ 
duce through the winter months. Thus several species which in the 
temperate conditions in the north hibernate only in the egg stage on 
their winter hosts, in the south pass the whole year on the summer 
hosts without suspending reproductive activity. Such a form is the 
Spinach Aphis ( Myzus persicoe). In the north the winter is passed in 
the egg stage on stone fruits and the resultant spring generations at 
times do much damage to these trees, but in the south the aphids feed 
on vegetable crops and weeds without performing their cycle on the 
fruit trees, this habit thereby eliminating injury to these tree hosts. 
Another such species is the Oat Aphis ( Aphis pruhifolice Fitch) which 
winters in the north on apple but in the south reproduces the year 
around on grasses and grains, and therefore in the semi-tropic zone 
apples escape injury from prunifolice. It should be stated, however, 
that due to their viviparous reproduction throughout winter both these 
species are liable to occur in spring on the summer hosts in greater 
abundance in the south than in the north, and thus the absence of 
injury to the fruit trees is counterbalanced by increased infestation on 
vegetable and grain crops. 
In considering the different aphid species of economic importance, 
it is found that in a few cases both the winter and summer hosts are 
economic plants. In this group we find Myzus persicoe, an aphid 
