Parasitic wasp Aphelinus asychis (copy)

The parasitic wasp Aphelinus asychis stings a Russian wheat aphid. The USDA has concluded that employing another parasitic wasp, Aphelinus hordei, would do no significant environmental damage.

Turning loose a non-native wasp to sting and kill an aphid that feasts on wheat and barley in the Western U.S. has received an environmental endorsement from the USDA’s Animal and Plant Health Inspection Service.

The wasp, Aphelinus hordei, a native of Eurasia, could be a weapon against Russian wheat aphids, an invasive bug found in 18 states, including Washington, Oregon, Idaho and California.

The USDA published in the Federal Register Tuesday a report on introducing the wasp to the U.S. under controlled conditions.

“Based on our assessment and other relevant data, releasing this biological control agent will not have a significant impact on the quality of the human environment,” according to the agency.

Russian wheat aphids were first detected in the U.S. in 1986 in Texas. The aphids caused hundreds of millions of dollars worth of damage over the following decade.

“It caused a huge problem because it was so abundant and injurious,” University of Idaho entomologist Sanford Eigenbrode said. “There was a lot of money spent on it across the country.”

Outbreaks have become more rare because of the development of resistant wheat and barley varieties, according to the USDA, but the agency warns that strains of Russian wheat aphids able to adapt to the new varieties began appearing in 2003.

Seeds treated with neonicotinoids could be an alternative to resistant wheat and barley varieties, but there is growing concern that neonicotinoids hurt pollinators, especially honey bees, according to the USDA assessment.

Insecticides are the most effective defense, and dimethoate, malathion and chlorpyrifos are commonly used, according to the USDA.

A coalition of state attorneys general, including from Washington, Oregon and California, is suing to force the Environmental Protection Agency to ban chlorpyrifos, alleging it’s a threat to human health. The EPA and farm groups are fighting the suit.

Russian wheat aphids are rare now, but it would be good to have another biological control on hand, Eigenbrode said. “It makes sense as added insurance.”

Laura Lavine, chairwoman of the Washington State University Department of Entomology, said the USDA has presented a strong case for using the wasp to control Russian wheat aphids. The wasps could benefit farmers, especially with the push to ban some pesticides, she said.

“I would say if you have the ability to introduce a biological control with a very low risk, you should always do it,” she said.

It’s likely that Aphelinus hordei, found in the Ukraine and the Republic of Georgia, have been naturally controlling Russian wheat aphids for more than 10,000 years, according to USDA’s assessment.

Female wasps sting the aphids with a tube-like organ. They either suck the hemolymph, an insect’s equivalent of blood, or lay eggs inside the aphid. The eggs hatch and the parasites eat their way out. In laboratory tests, female wasps killed more than 100 aphids in a two- to three-week lifespan.

The wasps are poor flyers and have limited range, and prey specifically on Russian wheat aphids. They are unlikely to stray far and their population should go down as they eat up the aphids, according to the USDA.

The aphids suck sap from plants and while feeding inject a toxin into the plant. The damage often appears as white streaks on the leaves and sometimes the stem. The aphids also transmit plant diseases such as barley yellow dwarf virus and barley stripe mosaic virus.

While the risks are low, the chances of success are low too, according to the USDA. Most biological controls fail.

The USDA will take comments on the assessment until June 4.

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