The Literature of Arthropods Associated with Alfalfa 
I. A BIBLIOGRAPHY OF THE SPOTTED ALFALFA APHID 
Therioaphis maculata (Buckton) (Homoptera: Aphidae) 
THE ALFALFA ECOSYSTEM is unique among field-crop 
systems in that it represents a relatively long-lasting, well- 
established, perennial system that exists nationally over 
a variety of climatic, geographical, and edaphic condi- 
tions. Because of these many subsystems, the interactions 
with other specific agroecosystems or natural systems are 
equally as varied. Alfalfa supports a wide variety of 
insects. These include destructive insects, pollinating in- 
sects, species that inhabit the fields because of the lush 
habitat but have little effect on the crop, and many other 
associated predators and parasites. Because of the peren- 
nial growth habits of alfalfa, many pest and beneficial 
insect species of other crops overwinter or build up in 
alfalfa before migrating to neighboring crops systems. 
Considerable laboratory and field data dealing with 
chemical, biological, and cultural methods of controlling 
alfalfa insects are available. These data need to be closely 
interpreted with respect to their implications for inte- 
grated control and then applied in integrated pest man- 
agement programs in the field. The breadth and depth 
of research on alfalfa insect control and alfalfa produc- 
tion in general have been sufficiently productive to im- 
plement some programs now. 
To facilitate better use of existing literature in devel- 
oping pest management systems, bibliographies of the 
key pest species on alfalfa are being prepared in coopera- 
tion with the Soybean Insect Research and Information 
Center (SIRIC) at the Illinois Natural History Survey 
and University of Illinois. SIRIC has developed a set 
of computer programs for the IBM/360 at the Univer- 
sity of Illinois, which makes possible the retrieval of liter- 
ature citations associated with a subject or combination 
of subjects. The bibliographies of the key alfalfa pests, 
starting with Therioaphis maculata have been stored on 
magnetic tape and are retrievable using the SIRIC 
system. 
Damage from the spotted alfalfa aphid was first recog- 
uized in the United States during 1954. When it was 
irst reported, most of the workers believed that it was a 
orm of the yellow clover aphid which had become 
idapted to alfalfa. Within a couple of years it was found 
hat this was not the case. The spotted alfalfa aphid was 
ipparently a new introduction into the United States 
rom the Near East. The first reports were from New 
This paper, in the Biological Notes series, is published with special project 
unds, Dr. D. Davis is a Professor of Entomology at Utah State Univer- 
ity. M. P. Nichols is a Research Associate, International Programs and 
itudies, University of Illinois. Dr. E. J. Armbrust is an Associate Entomol- 
gist at the Illinois Natural History Survey and Associate Professor of Ag- 
icultural Entomology, Illinois Agricultural Experiment Station. 
D. W. Davis, M. P. Nichols, and E. J. Armbrust 
Mexico, but it required only a couple of years for the 
aphid to spread throughout the southwestern part of the 
United States. Shortly thereafter it was widely distrib- 
uted through most of the country. It is still considered 
essentially a warm-climate insect best adapted to the 
southern tier of states. It has the ability, however, to 
spread rapidly on wind currents, so by mid- or late 
season, it often spreads well into the colder areas of the 
Rocky Mountains and Midwest. 
The spotted alfalfa aphid is much smaller than the 
pea aphid and can be readily distinguished both by size 
and color. It is yellowish with dark spots. It also pro- 
duces much more honeydew and can usually be recog- 
nized by the sticky mess. When disturbed, these aphids 
actively jump from the plants. Summer winged forms 
are produced in much larger numbers than the pea 
aphid. 
Damage to the alfalfa plant is of several types. The 
possibility of virus transmission has been discussed by 
several authors, but has never been verified. Many work- 
ers believe that the aphid is capable of producing a toxin 
which is injected into the alfalfa plants, helping to pro- 
duce symptoms. Young plants of susceptible varieties can 
tolerate very few aphids without being killed. The tre- 
mendous amounts of honeydew produced have created 
problems such as clogging of harvesting equipment. Mold 
growing on this honeydew reduces livestock acceptance 
of the alfalfa. Stunted plants, poor seed set, and short 
stand life are typical symptoms. 
The spotted alfalfa aphid is a one-host-plant aphid. 
It has a continuous life cycle on alfalfa and normally 
does not produce sexual forms in the fall. This means 
that the best survival of the aphid occurs in areas where 
there is alfalfa growth during the entire year. The adult 
aphids often crawl down around the base of the plant 
where they are capable of surviving during the winter 
unless the climate is too severe. In cold areas, there 
may be complete mortality. This is the basic reason that 
the spotted alfalfa aphid is a problem primarily in 
warmer climates. Starting about 3 years after its initial 
introduction into the United States, a few sexual forms 
were noted during the fall of the year. These sexual 
forms have never become numerous, but they are a pre- 
lude to egg laying on alfalfa stems. There is evidence 
that the spotted aphid populations in the northern areas, 
such as South Dakota and Minnesota, have been gradu- 
ally selecting for larger numbers of these sexual forms. 
Even with these fall egg-laying aphids, Medicago spp. 
