Before applying insecticides to 
alfalfa, thoroughly clean sprayers 
that have been used for herbicides. 
NATURAL CONTROL 
Weather that is favorable to rapid 
spring growth of alfalfa greatly re- 
duces the possibility of aphid dam- 
age. Aphid infestations may be 
wiped out by hot weather and re- 
tarded by cold weather. Heavy rains 
often dislodge and kill aphids. And 
warm spring weather is favorable 
to the development of their natural 
enemies. 
Many natural enemies — predatory 
and parasitic insects, and fungus 
diseases — attack the pea aphid and 
help controlit. Usually, they become 
Washington, D.C. 
abundant only when the aphid is 
abundant. 
The most numerous and beneficial 
predator is the convergent lady 
beetle (Hippodamia  convergens). 
Other predators include a few other 
beetles, larvae of lacewing flies 
and syrphid flies, and nabid nymphs. 
Several parasitic wasps attack the 
pea aphid. One species (Aphidius 
smithii) .was imported from India 
and released in California in 1958. 
It has become firmly established and 
is exerting considerable control of 
the pea aphid in certain areas. This 
species has been introduced into 
several other States. 
During periods of high humidity 
and warm nights, fungus diseases 
develop rapidly and are often of con- 
siderable importance in controlling 
the pea aphid. 
Issued May 1964 
For sale by the Superintendent of Documents, U.S. Government Printing Ofhce, Washington, D.C., 20402 - Price 5 cents. 
U.S. GOVERNMENT PRINTING OFFICE : 1964 OL—724-011 
