Regulation of Russian wheat aphid (Diuraphis noxia) populations with natural enemies present in the wheat system

A three year study of the influence of naturally occurring biological control on Russian wheat aphid abundance was performed at three eastern Colorado sites, Akron, Fort Collins and Lamar, using an exclusion cage approach. At each site, fully caged, partially caged and uncaged treatments were constructed. In general, fewer Russian wheat aphid and lower percentage infested and symptomatic tillers were found in the uncaged treatment than the caged treatment. Results suggest that natural enemies may have been responsible for the decline in aphid populations in the uncaged and partially caged plots. Natural enemies may be partially responsible for the year-to-year fluctuations in Russian wheat aphid activity currently observed in Colorado wheat growing areas. Previous studies documented low levels of biological control, however, it now seems that natural enemies, as well as climate, are the key determinants in Russian wheat aphid abundance in Colorado.