10 BULLETIN 826, U. S. DEPARTMENT OF AGRICULTURE. 
have developed aleyrodiform generations and wax secreting structures. 
In many ways the specialization of these insects is most remarkable. 
Key to the Subfamilies of the Aphididae. 
1. Sexual forms small with functioning mouth parts absent. Oviparous 
female with all the egg tubes present or indicated in the embryo but the 
adult possessing only one tube and maturing one cell so that one egg only 
is laid. Cornicles much reduced or absent. Wax glands abundantly 
developed. Wing veins usually reduced. Antenna! sensoria prom- 
inent Eriosomatixae. 
Sexual forms with functioning mouth parts. Nearly ail the ovarian tubes 
developed in the adult oviparous female 2. 
2. Radial sector of forewing inserted mesad of the stigma. Sexes small. Ovi- 
parous female laying several eggs Mindarinae . 
Radial sector not so inserted but arising from the stigma 3 . 
3. Forms usually gall makers. Wing veins much reduced so that the media is 
usually simple. Wax glands usual. Antennal sensoria annular. Aley- 
rodiform stages common. Sexes wingless as a rule and small. .Hormaphidixae. 
Forms not usually gall makers. Wing veins often not reduced. Wax 
glands not abundant. Antennal sensoria oval or subcircular. Aleyrodi- 
form stages rare. Cornicles often little reduced. Winged males common. 
Aphidixae . 
Subfamily I, APHIDINAE. 
The subfamily Aphidinae contains many of the most primitive 
insects in the family. Indeed, with the exception of the Mindarinae 
the subfamily may be considered as by far the most primitive. 
The oviparous female, in all the tribes, develops the ovaries in a 
normal way and lays several eggs. An exception to this, however, is 
the Thelaxini, but here two or more eggs are sometimes laid. The 
males may be either alate, apterous, or intermediate, and in many 
species which possess the migratory instinct they are often produced 
on quite a different food plant from the oviparous form. The stem 
mothers are in practically all cases apterous, but the remaining gener- 
ations throughout the year may or may not be winged. In many 
species a larger percentage of winged forms occurs in certain 
generations and a larger percentage of apterous forms in others. 
In some species, however, this does not appear to be the case. In 
certain of the Callipterini practically all of the viviparous forms other 
than stem mothers are winged. 
The insects are mainly foliage feeders, but they also attack the 
stems and roots. They occur both upon woody plants and herbs. 
Their feeding may have little apparent effect upon the host or it may 
cause distortions or pseudogalls. Some species are particularly in- 
jurious to their hosts and when these are economic plants cause much 
loss. 
Great variation is met with amongst the members of the subfamily. 
The antennas are rather long and slender and as a rule are armed 
with subcircular sensoria. In most of the forms the sixth segment 
