ECOLOGY OF THE RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) ON DRYLAND WINTER-WHEAT IN THE SOUTHERN UNITED-STATES

All three seasons that this research was conducted were drier than nor mal on the Texas High Plains. Temperatures were seasonal each year. Ap hid densities were low in the fall. Greenbugs, Schizaphis graminum (Ro ndani), and bird cherry-oat aphids, Rhopalosiphum padi (L.), were the most common aphid species on wheat in the fall. The most dramatic incr ease in densities of the Russian wheat aphid (RWA), Diuraphis noxia (M ordvilko), occurred in the spring. RWA survived cold winter temperatur es better than the other two species. Alates of RWA were recovered in November and December, indicating migration to wheat throughout the fa ll. Their low densities in the fall indicate that summer survival of R WA on the southern High Plains is poor. Although alates of RWA were fo und every month, large numbers of alates were not recovered until May when plants were senescing. Probably large migrations of Russian wheat aphids to states north of Texas do not occur until late spring. Densi ties of beneficial insects were very low on wheat indicating that nati ve predators and parasites probably are not very effective at reducing populations of RWA. High correlations between aphid densities and per centage of infested plants, infested and damaged plants or infested ti llers indicate that the numbers of RWA can be estimated when plants or tillers are used as the sampling unit.