26 BULLETIN 276, U. S. DEPARTMENT OF AGRICULTURE. 



LIFE HISTORY. 



The life history of the pea aphis is quite simple, for it does not 

 have a true alternate host like some species of plants-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 living 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. 1C. — Macrosiplium pisi from Russia: a, antenna of winged viviparous female; 6, 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 wingless and winged forms 

 being able to withstand the lower temperatures in that latitude. 

 Still farther south we know only the viviparous females and our obser- 

 vations lead us to believe that the species may reproduce viviparously 

 indefinitely in localities where the winters are quite mild. 



FIELD OBSERVATIONS. 



In the latitude of Illinois, Indiana, Maryland, and Delaware 

 mig rants 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 



