In 2008, a A fruit fly known as Drosophila spottedwings traveled from Southeast Asia to the continental United States, likely hitching a ride on the fruit shipment. The insect was first found in raspberry fields in California and quickly spread to other states.
Unlike common fruit flies, which are easily attracted to rotting food, spotted winged fruit flies prefer ripe, healthy fruit. Females use serrated, tubular organs to cut through the peel and lay their eggs inside. When the eggs hatch, the newborn larvae destroy crops. Invasive pests cause hundreds of millions of dollars in damages each year. To control them, growers rely on pesticides that kill insects indiscriminately, both pests and beneficial ones. But scientists are working on new solutions that could one day replace — or at least limit — the need to spray chemicals.
Last month, in a greenhouse in Oregon, USDA researchers began testing one such method: sterilizing male fruit flies. The gene-edited insects, made by St. Louis-based biotechnology company Agragene, are designed to suppress wild fly populations. The idea is that if they were released into the environment, the neutered males would mate with wild females, resulting in a fertility dead end. “We believe this technology can provide healthier fruits and vegetables without causing too much harm to the environment,” said Agragene CEO Bryan Witherbee.
The company’s scientists used the DNA-editing tool Crispr to knock out two important genes in fruit fly embryos — one related to male reproduction and the other to female development. As a result, only the sterile males hatch, while the females die. “You don’t want to release females into the population because those are the ones who are doing the damage,” said Stephanie Gamez, director of research and development at Agra Genes.
But before the company can release any gene-edited insects into the open air, it first has to test them in closed greenhouses. Working with government researchers and with permission from the U.S. Department of Agriculture, the company is testing how well gene-edited male fruit flies can reduce the number of non-edited flies in greenhouse conditions and prevent damage to blueberries grown there. The experiment will last two to three months.
The company is currently applying to the agency for field testing next year. Ultimately, Agrakin’s plan is to sell small cardboard boxes containing sterile male pupae—the stage before flies turn into adults. At this stage, the pupae are cocooned and immobile, making them easy to transport to farms. (Wetherby said the company tried shipping live adult flies, but some insects died in the process.) Boxes will be placed in fields, and when adult flies emerge, they seek out females.
Weatherby argues that a ratio of four or five neutered males to one wild insect is needed to wipe out a population, and the severity of a field infestation will determine how many insects are released. Since males are sterile, they do not produce offspring when mated with females. Spotted-winged flies live only a few weeks, so once the first generation of flies dies, repeated releases of gene-edited males are required to keep their numbers down. Weatherby said the company will start with weekly releases in the greenhouse experiments, but in the field, multiple releases over a shorter period of time may be required.