Soybeans with built-in bug repellent

IOWA STATE (US)—Researchers are exploring a method of controlling soybean aphids from within, without the use of pesticides.

Bryony Bonning, professor of entomology, and Allen Miller, professor of plant pathology, at Iowa State University are looking to genetically modify soybeans so they carry in-plant protection.

If the research is successful, the result will be similar to the way genetically modified corn now keeps the European Corn Borer from destroying corn yields, technology that has been in use for about 12 years.

Soybean aphid outbreaks have become an annual phenomenon in Iowa, Miller says. Left untreated, the loss in yield could exceed $250 million in the state. The annual cost to prevent the yield loss with insecticides can reach $64 million for Iowa soybean growers.

The researchers are focusing on introducing a gene into soybeans that is harmless to mammals, but creates a toxin that is lethal to aphids that feed on soybean plants. In order to be effective, the toxin needs to be ingested intact into the body cavity of the aphid, not broken down by the bug’s digestive system.

Miller and Bonning identified a plant virus coat protein eaten by soybean aphids that doesn’t break down and goes into the aphid body cavity intact. They then fused the toxin to the protein coat. Since the coat is the only part of the virus to be used, there is no risk of an infectious virus.

“What we thought was, if this (virus) protein has this ability to be taken up into the aphid (intact), let’s take advantage of that specialization and fuse that to other proteins that are toxic,” Miller explains.

Apart from curbing the aphid problem the technology also benefits farmers and the ecosystem, the researchers say. “The (potential) economic impact overall is huge,” says Bonning. “There will be less insecticide use, and also less fossil fuel used to apply the insecticides.”

Spraying soybeans with insecticides doesn’t just control the aphids, according to Bonning. “When you spray, you also control beneficial insects,” she explains. “Lady beetles are affected, for example, and they are a natural enemy of the aphids. So when the aphids come back to a field after spraying, there won’t be any lady beetles to naturally control the aphid populations.”

If growers spray for aphids and don’t eliminate them all, the aphids simply disperse to other fields, making the problem worse, Miller adds.

“There are many reasons not to spray, but you can’t tell the growers to stop spraying until you give them an alternative,” Bonning concludes.

The study is being funded by a Grow Iowa Values Fund Grant.

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