A new strain of Russian wheat aphid has been identified in Colorado by Colorado State University, causing crop losses on farms that still are recovering from the drought. Since the voracious original strain of Russian wheat aphid entered Colorado in 1986, it has cost the state’s 14,000 wheat farmers more than $132 million in crop losses and insecticide control efforts.
The aphid is attacking all wheat varieties this spring that were developed to be resistant to the original strain of the insect, especially in central and southern Colorado.
"A new biotype of the Russian wheat aphid is not a completely unexpected development, but there was no way to prepare for it because we could not forecast how the aphid would develop and what sources of resistance would be effective," said Frank Peairs, Colorado State University Cooperative Extension entomologist who, along with other experts at the university, has spent 17 years developing tactics to control the aphid.
In particular, Prairie Red, a variety of wheat that has been resistant to the aphid, is consistently infested with the new aphid biotype, known as biotype B.
Prairie Red contains the same Russian wheat aphid-resistant gene as the other resistant varieties developed by Colorado State University: Ankor, Halt, Prowers 99 and Yumar. Another resistant variety, Stanton, which was developed by Kansas State University, also is susceptible to infestations. Combined, these varieties account for about one-fourth of wheat acres in Colorado in 2003. All of these varieties continue to be resistant to the original aphid, known as biotype A.
Researchers are not sure if the new biotype adapted in response to resistant varieties of wheat or if it was introduced from another country, where different types of the insect exist.
The aphid damages wheat and other grains by injecting saliva into grain and sucking sap from plants. If left untreated, the aphid can destroy more than half of a crop. The aphids begin to appear in crops in April and May and their population peaks in July, the month most common for harvesting wheat in the state.
They often survive in host plants such as wheatgrass and barley and begin to winter in wheat crops in October and November, shortly after they are planted. The aphid can survive the winter in most areas of the state where wheat and grain is grown.
Farmers in Colorado have managed biotype A aphids with a combination of predatory insects, insecticides, controlling weeds that host the insect and by planting resistant varieties. In Colorado, 4.7 million acres has had to be treated with insecticides to control the aphid since 1986. This represents about 30 percent of the total wheat acreage in the United States. Aphids prevent young wheat leaves from flattening out, or unrolling, and live within the tubes formed by tightly curled leaves. This makes it difficult to kill the aphids with predatory insects and insecticides.