Jul 012003
Authors: Shandra Jordan

A new aphid biotype in Colorado is sending researchers at CSU back to the lab to create a new resistant strain of wheat that won’t be damaged by the new aphid.

In the 17 years since the first aphid biotype was identified, researchers at CSU have created five resistant wheat varieties. The new aphid, biotype B, causes damage to these resistant varieties.

A 2003 variety survey showed that 25 percent of Colorado’s wheat acreage is one of the varieties of wheat that is resistant to aphid biotype A, said Scott Haley, an associate professor and wheat breeder with the soil and crop sciences department.

Biotype B could have adapted from biotype A in response to the resistant wheat or it could have traveled from another country on the wind, said Frank Peairs, an entomology specialist with cooperative extension.

On a world-wide basis, there are many varieties of aphid, but these two biotypes are the only one’s seen of this strain in North America. Biotype A originally arrived in Colorado by traveling on the wind from Mexico, Peairs said.

The current bug has cost the state’s 14,000 wheat farmers more than $132 million.

In Colorado, 4.7 million acres treated with insecticide, or 30 percent of total acres in nation, according to a press release.

Because the aphid is variable in how it impacts fields, it is hard to predict the economic impact on growers.

Peairs estimated that a worst-case scenario is about a 50 percent yield loss while a typical range might be more like 20 to 30 percent.

Ron Meyer, area extension agronomist for CSU, said the impact could be similar to biotype A, which cost Colorado farmers more than $100 million.

Researchers at CSU have already begun development of a new wheat variety that would be resistant to the new aphid.

However, wheat is planted in September so it is unlikely that a resistant strain will be available for next year’s crop, Meyer said. Wheat producers will have to use insecticides for at least the next year.

Resistant wheat is developed by cross-pollinating a regular variety of wheat that grows well in Colorado with a resistant source, which might not grow as well in Colorado, Haley said.

“After several generations of selection and evaluation following that cross you hope to find a plant that has all the desirous genes you want,” Haley said.

Researchers have looked at about 16 to 19 sources of resistance, said Jerry Johnson, an extension specialist for crop production. Only one looks like it could work, but it might be associated with poor quality, Johnson said, so the researcher’s work continues.

“So much has already been done that we should be able to come up with some sort of form of resistance in a much shorter time,” Johnson said.

The most recent strain of wheat resistant to biotype A is Ankor, which was released this year, Johnson said.

Research will continue because the aphids will continue to adapt, Haley said.

“Trying to stay one step ahead of them is kind of difficult,” Haley said. “I think it’s surprising for this to be the first different biotype to be identified.”

In another type of aphid – the green bug – researchers have found a new one about every 5 years, Haley said.

“It’s a hint of what might happen,” Peairs said.

Despite the challenges, developing resistant plants is the best option for controlling the aphids, far superior to insecticides.

Developing resistant wheat is cheap compared to the cost of spraying, both to the farmer and the environment, Haley said.

While it might take about $1 million to develop a resistant strain of wheat, “it would cost dozens of millions to spray insecticides every year,” Haley said.

Wheat producers will have to use insecticides until a resistant strain of wheat is produced, Meyer said.

“Insecticides work well in controlling the aphid, but its an added cost to wheat producers and they would much rather have resistance,” Meyer said.

Right now, a lot of information is unknown about the new biotype, Johnson said.

“How widespread they are, if they’re going to survive, if they’re going to replace the other biotype, how effective they are against predators like lady bugs, we can’t take the risk of waiting to answer all those questions before we get going on the research,” Johnson said.

While researchers work on developing resistant wheat, Johnson encourages farmers to continue using the wheat resistant to biotype A and watch for signs of infestation by biotype B.

“Just because we got a new biotype doesn’t mean farmers should throw out the old resistant types. Until we can come up with a substitute, those should be used,” Johnson said. “Farmers should keep resistant lines and keep an eye to see if there are symptoms of infestation just like they had to scout in the old days for the original biotype.”

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