Checkoff-funded research works to combat devastating pest

December 11, 2024 | Kriss Nelson

The presence of soybean aphids poses a significant risk to soybeans. They cause considerable damage to soybean crops, resulting in a potential yield reduction of nearly 40% and the transmission of diseases that further compromise crop health.

The research on this destructive pest is crucial for developing effective management strategies for growers.

Shocking discovery of a new soybean pest

Iowa Soybean Association (ISA) District 1 Director Paul Kassel reflects on discovering the pest 24 years ago when he was an Iowa State University (ISU) Extension agronomist.

“I stopped to check maturity progress in a random soybean field when I first saw soybean aphids,” Kassel says. “It was near Ringsted in a Pioneer variety plot in 2001.”

Two years later, this new-to-America pest became an issue. Kassel remembers phone calls flooding in between July and August 2003.

“I had never experienced such a widespread and devastating insect problem,” he says. “Everyone — farmers, dealers, applicators and ISU Extension, including myself, had a difficult time grasping the seriousness of this insect.”

“It was almost like people hit the panic button,” says ISA Research Agronomist Drew Clemmensen. “They found this insect; they didn’t know what it was, and suddenly, it was appearing in their neighbor’s
fields and was spreading to every acre, causing devastation.”

Because the pest was new to the state, there was no way to predict the impact of what a soybean aphid could have on soybean yields.

Soybean industry experts and farmers turned to the potential of spraying insecticide, but that decision did not come lightly.

“Complicating the treatment decision was the dry weather of August 2003. Many areas received little rainfall in late summer,” says Kassel. “Hindsight, we should have applied insecticide to every soybean acre in northwest Iowa that August. The dry weather made the aphid’s impact much greater.”

Researching the aphid

ISA soon leveraged checkoff dollars to fund research on the soybean aphid, which has now turned into one of the longest soybean checkoff-funded studies at ISU.

“This pest has the potential to cause significant damage and destruction,” says Clemmensen. “Research can uncover more details about the pest, giving us solid data on its destructive effects and deepening our understanding. It’s crucial to shed light on how devastating it can be.”

Matt O’Neal, ISU professor in the Department of Plant Pathology, Entomology and Microbiology and Wallace Chair for Sustainable Agriculture, says the checkoff has funded multiple methods to survey and manage soybean aphids.

“This includes developing scouting tools so farmers know when aphids are present and need to be treated, testing existing and novel insecticides and selecting and evaluating aphid-resistant soybeans,” says O’Neal, who also serves as the director for graduate education for entomology at ISU. “Checkoff funding has also invested in more basic topics, like sequencing the genome of the soybean aphid, especially those resistant to insecticides.”

Through more than two decades of soybean aphid research, O’Neal’s team has also studied insects that feed on the aphid. One approach to combating the aphid is introducing parasitoid wasps from China, where the aphid originates. As a result, at least two parasitoid wasps have established in Iowa to control population numbers.

Clemmensen says growers should be aware of beneficial insects when deciding whether to use insecticides to manage soybean aphids.

“Beneficial insects can help keep soybean aphid populations under control,” he says. “We need to manage insecticide applications so they do not kill beneficials.”

Researching this major threat to soybeans has now expanded to explore insecticide resistance. A three-year survey of commercial fields in Iowa examined the occurrence of insecticide resistant aphids before and after spraying.

“We have been seeing a high level of tolerance to pyrethroids and resistance as well,” says Clemmensen. “We need this research to understand what chemistries we can use to control soybean aphids.”

O’Neal’s research revealed that 100% of the 2,500 soybean aphids tested carry at least one gene associated with resistance to pyrethroids.

“We are now exploring if the probes made from RNA (ribonucleic acid) based on the mutations that produced resistance can be used to selectively kill insecticide-resistant aphids,” says O’Neal. “In this way, we hope to take advantage of the growing commercial interest in RNAi technology to help soybean farmers fight back against insecticide resistance.”

Due to the scale of the project, research continues, more than 20 years later.

“We have another 2,000 aphids to analyze through our DNA sequencing protocol,” he says. “This data will tell us how common insecticide-resistant aphids are and which mutations are the most common.”

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