To fight berry-busting fruit flies, researchers focus on sterilizing the bugs

Paul Nelson is used to doing battle with an invasive fruit fly called the spotted wing drosophila, a pest that one year ruined more than half the berries on the Minnesota farm he and his team run. In recent years, they’ve cut their losses closer to 5%, but it’s been labor-intensive and expensive.

“It’s a pest that if you’re not willing to stick the time into it, it’s going to take over your farm,” said Nelson, the head grower at Untiedt’s, a vegetable and fruit operation about an hour west of Minneapolis.

Nelson and other growers may someday get a new tool as a result of research at North Carolina State University into the insects, which ruin the berries by laying their eggs in them and have been estimated to cost growers hundreds of millions of dollars annually. The researchers, using a concept called “gene drive,” manipulated the insects’ DNA so that the female offspring would be sterile, and the method they used to achieve it significantly reduced the chance that a population could rebound.

The researchers, whose work was published Monday in the Proceedings of the National Academy of Sciences, found if they bred one of their modified flies with a non-modified fly, up to 99% of the offspring would inherit the sterility trait. They used mathematical modeling to show that if they released one modified fruit fly for every four that were not and did that every two weeks, they could collapse a population in about five months.

Genetically modifying insects as a form of pest control isn’t a new idea. Scientists have already released genetically modified mosquitoes, for instance, which mate with the native population to produce offspring that die before adulthood to hold down populations and help combat the spread of insect-borne diseases like yellow fever, dengue and Zika viruses. But the technology hasn’t taken off as widely in agriculture because pesticides have been cheaper and easier to deploy.

Max Scott, a professor of entomology and a co-author of the paper, said some methods of releasing genetically modified insects to curb populations would become expensive if applied on a large scale because it has to be done over and over again before pests are wiped out. But he said his team’s method, which hinges on an idea called “gene drive,” more quickly facilitates the spread of sterility throughout successive generations, and that could mean fewer times the modified bugs need to be released.

“We’re really excited about this,” Scott said. “The system is working really efficiently.”

If the researchers’ genetic process works in the field, it could be an important addition to farmers’ arsenal of pest management techniques against a persistent bug that can wipe out 2030% of a raspberry yield even after pesticide use, said Bill Hutchison, a professor and extension entomologist with the University of Minnesota. And the fight against pests has been growing with climate change, he added, as warmer winters are allowing invasive species like the spotted wing drosophila to better survive the winter and extend their range for overwintering north.