Numbers
There are about 40 recognized Schizaphis species worldwide with seven known from North America (Blackman and Eastop 2000).
Print References
Blackman, R.L. and V.F. Eastop. 2000. Aphids on the World's Crops, An Identification and Information Guide, 2nd Edition. John Wiley & Sons Ltd., England.
Internet References
Greenbug - Featured Creatures, Univ. Florida