52 BULLETIN 276, U. S. DEPAETMEis'T 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 T^rriters, which we are able to corroborate, the common aphis 
fmigus, Empusa apliidis (fig. 13), is the most important natural check 
on the increase of MacrosipJium- pisi. This fungus thrives under 
first turn brownish and later become covered with the fungus threads. 
Thus weather conditions favorable for the growth of Empusa fimgus 
are indirectly important. Furthermore, driving rains destroy great 
numbers of these plant hce, and very hot, dry weather seems to 
Fig, 14. — The convergent lady-beelle (Ilippodamia convcrgens), an enemy of Macrosiphum 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, Hippodamia convergens Guer. (fig. 14), 
which is probably the most generally common and abundant of all 
the ladybirds; 11. glacialis Fal)., //. lo-punctata L., 11. j^fi'i^enthesis 
Say, Cydoneda munda Say, CoccineUa 9-notata Hbst., MegiUa fusd- 
TiG. l^.— 3facrosiphum pisi attacked by a fimgus. 
Enlarged. (Original.) 
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 Tv^ith 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 
