UNITED STATES DEPARTMENT OF AGRICULTURE 
Washington, D. C. PROFESSIONAL PAPKR September 29, 1915 
THE PEA APHIS WITH RELATION TO FORAGE 
CROPS. 
By J. J. Davis, 
Entomological Assistant, Cereal and Forage Insect Investigations. 
CONTENTS. 
Page. 
Introduction 1 
Synonymy 2 
Identity of the species occurring in America. 4 
Past history of the pest and its injuries 5 
Character of attack 7 
Effects on cattle of feeding them infested 
clover 7 
Distribution and origin 8 
Food plants 9 
Description 12 
Life history 26 
Field observations 26 
Page. 
Generation experiments 27 
Ilatching of the egg 43 
Molting 43 
Age at which females begin reproducing 45 
R eproducti ve period 49 
Longevity 49 
Fecundity of viviparous females 49 
Sexual forms 50 
Fecvmdity of oviparous females 51 
Natural control 52 
Methods of artificial control 54 
INTRODUCTION. 
The periodic occiirrenc-o of the pea aphis ( Macrosiphum jnsi Kalt.) 
in unusual abunchxnce on various k^guminous crops, more especially 
red and crimson clovers, vetches, field and garden peas, and sweet peas, 
has placed it among the important injm'ious insects of the world, for it 
is ahnost cosmopolitan and more or less mjiu^ious wherever found. In 
Europe it has been the subject of numerous treatises, both from the 
systematic and economic vie^\q)oints, and its identity has been much 
confused with other closely related species. In America it seems to 
have made its first appearance in destructive and noticeable numbers 
in 1S99, although it is kno^^^l to have been present here for at least 
two decades previous, and each year since 1899 this apliis lias boon 
recorded as injurious in one or more localities in the United States. 
In the present paper we have attempt'od especially to settle the 
identity of the species, an important it-em from the economic stand- 
point, and to report our extended life-history investigations, together 
with a summary of all the important facts, both old and new, relative 
to the life economy of the species. 
98034°— Bull. 276—15 1 
