ECONOMIC INJURY LEVELS FOR THE RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) ON WINTER-WHEAT IN SEVERAL CLIMATE ZONES

Research was conducted in 4 states (Colorado, Montana Texas, and Washi ngton) to determine the economic injury level for the Russian wheat ap hid, Diuraphis noxia (Kurdjumov), as affected by climate zone and whea t growth stage. Fall infestations were established on winter wheat at the 2-leaf and 2-tiller growth stages. Russian wheat aphid infestation s did not develop well on the 2-tiller stage wheat because late fall t emperatures became too cold before the infestation period was complete . In the coldest climate zones, where winter kill of wheat becomes a f actor, the loss value for 2-leaf wheat will be 1% per percentage infes ted or damaged tillers and 1.1% per infestation or damage day. This wa s 3 times greater than the loss in the southern climate of Texas and 1 .6 times greater than the loss in the Pacific Northwest (Washington). Therefore, different fall infestation economic injury levels will be u sed in different climate zones in the United States. Russian wheat aph id infestations on winter wheat were initiated in the spring at spring regrowth, one node, and boot growth stages. Losses from Russian wheat aphid infestations in Colorado in the spring were similar to those re ported in earlier research in Texas, 0.5% loss in bulk seed weight per percentage of infested or damaged tillers.