52 



BULLETIN 276, U. S. DEPARTMENT OF AGRICULTURE. 



NATURAL CONTROL. 



It is doubtful if any species of plant louse is more harassed by 

 enemies than is the pea aphis. According to the observations of 

 other writers, which we are able to corroborate, the common aphis 

 fungus, Empusa aphidis (fig. 13), is the most important natural check 

 on the increase of Macrosiplium pisi. This fungus thrives under 



moist conditions, especially 

 when accompanied by warmth, 

 and hence it usually makes its 

 appearance after a few days of 

 rainy weather and more often 

 in summer — that is, during the 

 warmer months. As might be 

 inferred, this fungus is conta- 

 gious and spreads with wonder- 

 ful rapidity, frequently, as ob- 

 served by us, so completely 

 eradicating the insects that it 

 was difficult and sometimes im- 

 possible to locate a single living 

 plant louse. Diseased aphids 

 first turn brownish and later become covered with the fungus threads. 

 Thus weather conditions favorable for the growth of Empusa fungus 

 are indirectly important. Furthermore, driving rains destroy great 

 numbers of these plant lice, and very hot, dry weather seems to 



Tig. 13. 



- Macrosiphum pisi attacked by a fungus. 

 Enlarged. (Original.) 



Fig. 14. — The convergent lady-beetle (Ilipportamia convergent) , an enemy of Macrosiplium pisi: a, Adult; 

 6, pupa; c, larva. Enlarged. (From Chittenden.) 



hinder excessive multiplication, so that weather conditions are a great 

 factor in the natural control of this pest. 



Next in importance in the natural control of this aphidid are the 

 ladybirds, and of these no less than nine different kinds are known 

 to prey upon it, namely, Uippodamia converges s Guer. (fig. 14), 

 which is probably the most generally common and abundant of all 

 the ladybirds; If. glacialis Fab., JT. 18-punctata L. ; //. parenthesis 

 Say, Cydoneda munda, Say, Coccinella 9-notata Ilbst., MegiUa fusci- 



