Boy scientist in Manayunk finds sweetener that kills fruit flies

Simon Kaschock-Marenda, 14, and his father, Daniel Marenda, a Drexel University biologist. Simon and his dad are among the authors of new research showing that the main ingredient in the sweetener Truvia is toxic to fruit flies. Credit: Kirsten Kaschock

Simon Kaschock-Marenda needed a science project for his sixth-grade class at Masterman School and was intrigued by the fact that his parents had just cut back on sugar in their diet.

Because his father, Drexel University biologist Daniel Marenda, worked with fruit flies, the boy thought it might be interesting to feed sugar and other sweeteners to some flies.

Was it ever. Regular sugar was OK, but the flies that ate the sweetener Truvia were dead within a few days.

Daniel Marenda was skeptical, so he helped his son redo the experiment.

Same thing.

Three years later, that school project has turned into a full-fledged study, published online Wednesday in the journal PLOS One. The final research was conducted by Drexel faculty and graduate students, but listed among the coauthors is Kaschock-Marenda, now 14 and finishing up ninth grade.

"I was really excited, because I've never had anything published before," the young scientist said this week.

Truvia, made by Cargill, is known to contain an extract from the stevia plant, but it turned out stevia was not the culprit. Flies that ate Pure Via, another stevia-containing sweetener, were fine.

The researchers reported that the problem for the flies was an ingredient called erythritol, a naturally occurring sweetener from a family of compounds called sugar alcohols. Erythritol is considered safe for people. It is widely used as a food additive and is present in melons and grapes. So the Drexel scientists have hopes it can be used as a nontoxic pesticide.

The university has started the process to obtain a patent on using erythritol in this manner, said Drexel professor Sean O'Donnell, an entomologist who collaborated with Marenda on the study.

"You've got a compound that you could deploy for insect control with no concern" for human health, O'Donnell said.

The fruit flies in the study were of the species Drosophila melanogaster, widely used in lab studies. Such flies are not a huge problem for farmers because they go after fruit that is damaged or rotting, said Peter Shearer, an entomology professor at Oregon State University.

A much bigger problem is its spotted-winged cousin Drosophila suzukii, which can pierce the skin of ripening, healthy fruits still on the bush or tree. This pest was first seen on the West Coast in 2008, and has caused millions of dollars of damage to berries and cherries, said Shearer, formerly of Rutgers University. The insect has since been reported in Pennsylvania and New Jersey.

Shearer said that it was not necessarily true that if erythritol kills lab flies it would also be effective against D. suzukii but that it was worth trying. He also urged the researchers to examine whether erythritol is toxic to the flies or whether the insects died because the compound has no nutritional value.

Either way, the study is promising, agreed entomologist Robert K. Vander Meer, a research leader at the USDA's Agricultural Research Service in Gainesville, Fla.

"That's very interesting," Vander Meer said. "I don't think it's been reported that any sugar alcohol has controlling effects on insects that feed on them."

For the elementary school project that started it all, Kaschock-Marenda kept his vials of flies on his bedroom closet shelf in Manayunk. He put different sweeteners in each vial, mixed with growth medium.

The flies in the Truvia vial died within six days.

"Initially, I thought that we screwed up," his father said. "He made a mistake, or I made a mistake, or something's wrong."

They did the experiment again, in a Drexel lab with controlled temperature and humidity, with multiple vials of flies for each sweetener. Same result.

The full academic study was undertaken two years later, when Marenda, whose primary work is in neurobiology, happened to mention the results to O'Donnell, his entomologist colleague. Flies whose food contained erythritol lived for just a few days, while those eating all the other sweeteners lasted five to seven weeks.

It is unclear why the compound killed the flies, the scientists said. Those that ate erythritol also suffered from impaired motor coordination.

Marenda and O'Donnell said erythritol would not be useful for spraying on plants, as it is water soluble. A better option would be to place it in a baited trap.

Kaschock-Marenda, an avid guitar player, is living in Upstate New York this year while his mother, Kirsten Kaschock, is a visiting professor of creative writing at St. Lawrence University.

He will attend 10th grade next year at Masterman, where he is remembered as a serious, hardworking student, said Paula Conzelman, his science teacher in sixth grade.

Yet when the study was just a school project, the science fair judges were not bowled over by the results. Simon did not win a prize.

Conzelman now concedes Simon was onto something, with a published paper to his name.

"I'm very impressed," she said. "What a nice thing for him to put on his biography for his college applications."