26 BULLETIN 276^ U. S. DEPARTMENT OF AGRICULTURE. 
LIFE fflSTORY. 
The life history of the pea aphis is quite simple, for it does not 
have a true alternate host like some species of plant-lice. As has 
been noted, it attacks leguminous plants primarily, some of which 
are annuals, others perennials. Clovers, particularly red and crimson 
clovers, serve as hosts for this insect the entire year, and it is on these 
plants that it usually passes the winter, either as eggs or as viviparous 
females, although during the summer months the migrants also pass 
to other leguminous crops, such as sweet pea, garden and field peas, 
and vetches, and on these they multiply very rapidly, oftentimes, 
destroying large acreages. In the latitude of La Fayette, Ind., the 
species winters both as hving viviparous females, usually wingless, 
and as eggs. Farther north it may winter exclusively in the egg 
stage, although our observations are not complete on this point, 
Fig. 10.— Macrosiphum pisi from Russia: a, antenna of winged viviparous female; b, antenna of wingless 
viviparous female; c, cornicle of winged viviparous female; d, cornicle of wingless viviparous female. 
Greatly enlarged. (Original.) 
while farther south, in the latitude of Tennessee, the sexual forms 
which lay the overwintering eggs are rare, the insect ordinarily pass- 
ing the winter as living plant-lice, both mngless and winged forms 
being able to withstand the lower temperatures in that latitude. 
Stni farther south we know only the viviparous females and our obser- 
vations lead us to believe that the species may reproduce viviparously 
indefijiitely in locaUties where the ^\"inters are quite mild. 
FIELD OBSERVATIONS. 
In the latitude of Illinois, Indiana, Maryland, and Delaware 
migrants from the winter hosts, namely, red clover and crimson 
clovers, begin to spread to new fields of clover and to garden peas 
about May 1, and the injury to these crops usually becomes notice- 
able about June 1, extending up to July. Ordinarily by this time the 
parasitic and predacious enemies have become sufficiently numerous 
