The Heat Is On: WSU Food Engineer Works to Commercialize Radio Frequency Treatments for Insect Pest Control

PULLMAN, Wash.—The irony probably wasn’t lost on Washington State University food engineer Juming Tang.

Tang recently opened a bottle of lotus seeds to put in soup and smelled mold, a telltale sign that insect pests had already begun eating without him. Larvae hatched from eggs laid in the seeds create a moist environment for the mold to grow in—and to release toxins. Tang and a multidisciplinary, multistate team have been working for the last 12 years to develop and commercialize a method of treating nuts and legumes with radio frequency (RF) energy to combat such pests.

WSU Food Engineer Juming Tang
Washington State University Food Engineer Juming Tang examines a thermal image of a sample of lentils treated with radio frequency energy for insect pest control. Click image for a high-resolution version.

“People think that prepackaged dry food is safe, but this may not always be true,” he said. “RF treatment right after seeds are harvested but before storage can control pests before the larvae hatch or at a very immature stage. We believe it’s going to be a big thing.”

The nut and legume industries need a more environmentally friendly means of controlling such insect pests as codling moth, naval orangeworm, Indianmeal moth and cowpea weevil. In 2005 the U.S. Environmental Protection Agency phased out the industries’ main chemical fumigant used in postharvest pest control, methyl bromide, because of its harmful effects on the earth’s atmosphere.

Other nonchemical pest control methods exist—controlled atmosphere treatments, cold storage, conventional heating and irradiation—but have drawbacks, Tang said.

Controlled atmosphere treatments, where oxygen, carbon dioxide and nitrogen concentrations as well as temperature and humidity are regulated, require exposure times of several days, particularly for walnuts. Cold storage may take several weeks to kill insect pests. Conventional heating, including forced hot air and hot water treatments, cuts exposure time to hours, but can also cause external and internal damage to agricultural commodities. And irradiation, at low levels, merely sterilizes, but doesn’t kill, insects.

RF treatments, on the other hand, can achieve the same insect mortality rates as other methods in a shorter time, Tang said. RF treatment systems generate high-frequency electromagnetic waves that cause agricultural products—and insects—to heat rapidly. Shorter exposure times have the added benefit of not degrading food quality.

Juming Tang research team
Part of Juming Tang’s research team, from left to right: WSU doctoral student Yang Jiao, Juming Tang and WSU postdoctoral student Shunshan Jiao. Click image for a high-resolution version.

Tang, Shaojin Wang, a WSU adjunct professor of biological systems engineering, and other members of Tang’s team have conducted several studies on RF treatments of codling moth, navel orangeworm, Indianmeal moth and cowpea weevil through all life stages. Their research showed that complete insect mortality occurs between 4 and 10 minutes at temperatures varying from 50 to 60 degrees Celsius (122 to 140 degrees Fahrenheit).

“This is a very exciting development,” he said. “We started from concept development to establishing a fundamental understanding of insect heat resistance at different life stages and developed treatment protocols with pilot-scale RF systems here at WSU. We then scaled up and validated an RF treatment for insect control in in-shell walnuts at a large commercial facility in California.”

The work on RF treatments started in 2000, funded by the U.S. Department of Agriculture’s Initiative for Future Agriculture and Food Systems. The original team involved engineers, entomologists and plant physiologists from the University of California-Davis and USDA’s Agricultural Research Service in Washington, California, Texas and Hilo, Hawaii. Today, the team has expanded studies on RF treatments for legumes, raisins and other dry commodities.

So it’s likely that someday, when Tang opens another bottle of lotus seeds, it will have gone through a pest control system he developed here in Pullman.

“I think this technology is ready to be picked up,” he said. “Several companies and research institutions in China, Turkey and Taiwan are interested in adapting this technology for pest control in dry products, such as rice and dates. This may become one of the most successful methods for the physical treatment of postharvest pests in dry commodities.”