50 SEVENTEENTH Report STATE ENTOMOLOGIST OF MINNESOTA—1918 
colony in a protective covering; some find their protection in folded 
leaves, or in galls; many find their protection under ground on roots 
of plants. 
The number of generations for the season varies greatly; while 
some produce only a few, in others the generations follow in rapid 
succession. The successive generations may show considerable differ- 
ences in structure, so much so that they would easily be considered as 
different insects. The following five types of generations may be con- 
sidered as typical of the family. First, the fundatrix (foundress or 
stem-mother), the individual that comes from the egg and gives rise 
to the following generation; the fundatrix is always apterous. Sec- 
ond, the spuriae (wingless viviparous females or spuriae apterae) ; the 
second may have a number of successive generations all alike. Third, 
the migrants (winged viviparous females or spuriae alatae vel mi- 
grantes), which acquire wings and serve for the distribution of the 
colony; this generation may be followed by one or more generations of 
spuriae that are counterparts of the second type. Fourth, the sex- 
uparae, the last generation of spuriae (apterous or alate) with which 
the parthenogenetic mode of reproduction comes to an end for the 
season and which produces the following type. Fifth, the sexuales or 
true sex forms, the males and females, which, after copulation, pro- 
duce the true ova which remain over winter for the next season. 
While the females are always apterous, the males may be either alate 
or apterous. The succession of generations in the order given may be 
considered as typical of the family, to which many exceptions are 
found in the different groups. Thus the second generation may be com- 
posed of migrants, followed by spuriae, or there may be several gen- 
erations of migrants following each other or at various times during 
the season; a generation of spuriae may produce in part spuriae and 
in part migrants. Aphids appear to be greatly influenced by external 
changes and conditions; under favorable conditions they will continue 
to produce generation upon generation of spuriae, but with changed 
conditions of temperature and nature of the food only migrants are 
produced. The Callipterina constitute a remarkable exception in that 
all the parthenogenetic generations acquire wings before reproducing. 
Aphids feed upon juices of plants. The part of the plant to 
which they have become adapted is various but may be considered 
under the following heads. First, the bark feeders (corticola), found 
on woody parts of trees and other woody plants. Second, the root 
feeders (radicola), feeding underground at base of the trunk or on 
roots. This type may be considered as an early adaptation of the 
first type and is common in the Pemphiginae. Third, the leaf feeders 
