Research was conducted on the biology of cereal and grass aphids in the Madison area during 1957-59 in connection with epidemiological investigations of the barley yellow dwarf virus (BYDV). It becomes of increasing importance to know more about these aphids as potential vectors of the virus. Information was needed on the taxonomy, biology and ecology of the vector population to better understand the complex interactions between vector and virus. Two methods were used to obtain data on the occurrence and abundance of aphids. The conventional method of studying aphid populations on host plants was supplemented with intensive research on air-borne aphids, using the yellow-pan water trap developed by Moericke (1951), and the wind trap described by Shands (1942). These traps are shown in Fig. 1. The species of aphids were identified according to keys of Palmer (1952). Names of genera as used in Europe have been indicated in parentheses. In the following report the various forms in the life cycle are referred to as fundatrices (on the winter host), fundatrigenae (produced by fundatrices, the alates of this generation migrate to summer hosts), virginoparae (both apterous and alate individuals on snmmer hosts), and gynoparae (alates migrate from summer hosts to winter hosts).