Researchers Pit Lasers Against Sweetpotato Pest

The project has a mouthful of a name — Development of Nonchemical Control Strategies for Vinegar Flies in Storage — but in casual conversation, N.C. Plant Sciences Initiative researchers call it Fly Wars.

The sobriquet is a play on Star Wars, a nickname for the Strategic Defense Initiative touted by President Ronald Reagan in the 1980s. Just as Reagan wanted to shoot missiles out of the sky with lasers, an entomologist, a plant pathologist, an electrical engineer and their students at NC State University want to see if they can develop a feasible way to use lasers to kill pesky vinegar flies in sweetpotato storage facilities.

The flies have proven to be a nuisance to workers and led to complaints from people living near some sweetpotato storage facilities.

Anders Huseth, an associate professor in the Department of Entomology and Plant Pathology, has been conducting research on the vinegar fly problem for seven years. In parallel, Lina Quesada-Ocampo was studying flies as a key vector for pathogen spread in sweetpotato storage facilities. In team conversations with Michael Kudenov, a professor in the Department of Electrical and Computer Engineering, the idea of using lasers came up.

Kudenov knew that lasers had been shown to work against mosquitoes, so he decided to explore the idea of using them against vinegar flies. The team won funding from the N.C. Sweetpotato Commission and N.C. Agricultural Foundation to mentor graduate students on the project.

Getting to the Root of the Problem

To understand the problem and why it matters, it helps to know a little about sweetpotato production and marketing: Sweetpotatoes are North Carolina’s No. 4 crop, worth $305 million a year, and the state leads the U.S. in production. The plants’ roots — the part we eat — are typically harvested September, October and November, cured, then put into storage so they can be sold year-round.

In 2017, soon after he was hired at NC State, Huseth got calls from growers about fly problems in the storage facilities.

“We did some farm visits and discovered that the fly populations in the spring of the year, when temperatures are starting to increase, were growing almost exponentially, to the point where you really couldn’t open your mouth in the storage facility because you’d get flies in,” Huseth explains.

Around the same time, NC State plant pathologist Lina Quesada-Ocampo had noticed an uptick in the incidence of black rot, a common and economically important disease affecting stored sweetpotatoes. The two wondered what kind of fruit flies and vinegar flies were present and if any of them could be spreading the pathogens. Subsequent research with NC State entomologist Matt Berton showed that flies of the species Drosophila hydei were not only present in high numbers, they were also attracted to rotting roots and could spread the black rot pathogen among sweetpotatoes in a storage building.

“We don’t know that the flies are actively compromising the quality of the crop. What we do know is that the flies are finding rotting roots, and then they go rest on other potatoes and they go all over the storage house and the reproductive parts of the pathogen can get dispersed,” Huseth explains.

The Need for a Novel Solution

Some growers were spraying with chemicals to get rid of the flies, while others relied on cultural practices like keeping the facilities free from the damaged sweetpotatoes that attract the flies. Each strategy had drawbacks.

Cultural control is expensive, because it requires extra labor. Using vinegar traps is an option, too. But as Shea Phillips, a master’s student in entomology points out, there are costs, as well as what she calls “an ick factor.”

The insecticides they are using are costly and … becoming less effective. That’s why we are looking for other management options.

And while spraying can work, it’s also costly and sometimes counterproductive. For one thing, Huseth says, there are trade barriers for pesticides commonly used on sweetpotatoes. One of the disease-fighting pesticides that works the best against black rot is strictly regulated by the European Union and in the United Kingdom, both important markets for North Carolina sweetpotato exports.

Not only that, vinegar flies reproduce quickly, and when the organic pesticide pyrethrum is used repeatedly to combat the flies, it stops working as the flies develop a resistance to it.

As Joshua Larsen, one of Kudenov’s Ph.D. students, explains, “We can talk about how a good pesticide can kill 99.9% of them — great, right? But the flies breed super quickly, so they’re back again soon. There’s just not a lot you can do.”

Huseth thinks that putting another tool in growers’ fly-fighting arsenal is imperative. “The insecticides they are using are costly and largely are declining in efficacy — they are becoming less effective. That’s why we are looking for other management options.”

Moving the Laser Idea Forward

Huseth’s student, Phillips, has been studying management options for the resistance issues and also supplying Larsen with vinegar flies to use in Kudenov’s laser-equipped lab in NC State’s Plant Sciences Building.

Larsen is working with Kudenov to move the laser control idea from theory to reality.

“So far, we are seeing that yes, in the lab, it can work,” Larsen  says. “We can actually hit them from some distance away and get the results we want.

“When the blue laser hits them, the fluids inside them become vaporized, and there’s just no surviving,” Larsen adds. “And there’s really not a way for them to become resistant to a laser, because to become resistant, you have to survive.”

What’s Next

The researchers have figured out the right wavelengths and minimum laser power needed to kill the flies in a controlled lab setting, and within the year, they hope to deploy the Fly Wars system in a storage facility where it can be tested under the types of conditions that growers face every day.

That’s with no kind of chemical residue on the produce and no kind of resistance that can be built up.

Since workers go in and out of the warehouses frequently, safety is a concern with the lasers, and that’s why Larsen foresees the laser system working only at night, when the workers have left.

“If for eight hours every night you could just turn the system on and it kills just one fly a second, you’re taking out thousands of flies over the course of the night,” he says. “That’s with no kind of chemical residue on the produce and no kind of resistance that can be built up.”

As Huseth puts it, “The benefits at the end of the day could be great for the sweetpotato packers.”