Genetically modified diamondback moths designed to wipe out wild pest populations were released in fields for the first time in New York state.
Diamondback moths are migratory pests found in the Americas, Europe, New Zealand and Southeast Asia, but especially in areas where crops can be grown yearround.
In these parts – where it’s not too hot nor too cold – are where diamondback moths cause the greatest problems, including billions of dollars in damages to cruciferous crops such as cabbage, broccoli, cauliflower and canola. They’re one of the most damaging insects because of their high reproduction rate and resistance to most insecticides.
To address these problems in a sustainable, environmentally friendly way, researchers have successfully genetically engineered (GE) male diamondback moths to control the pest population of their wild counterparts, according to findings published Wednesday in the journal Frontiers in Bioengineering and Biotechnology.
“There’s a lot of interest in using genetically engineered insects for controlling medically important diseases,” said Anthony Shelton, lead author of the study and entomology professor at Cornell University’s College of Agriculture and Life Sciences.
“In agriculture, though, I think we can take the advantage of genetically engineered insects to control a major pest species.”
Engineering a self-limiting strain of moths
The moths were engineered by Oxitec, a developer of insect biological control systems that is known for its modified mosquito releases to reduce mosquitoes that carry malaria or dengue fever.
When rearing the moths, developers incorporated what they call a self-limiting gene that makes female offspring die shortly after hatching.
Typically, tetracycline, an antibiotic used to suppress the gene, is included in the moths’ diet so that female moths can be produced as well.
“However, when you want to release populations of males, you do not include tetracycline,” Shelton said. “So all the female larvae that are feeding on the artificial diet will die. And then you’ll just have thousands and thousands of males which you can release in the field.”
In cabbage field studies in Geneva, New York (about 260 miles from New York City) the moths were marked with different fluorescent powders, released together, then captured in a trap. The GE moths behaved similarly to their wild counterparts in regard to factors that would determine their potential to suppress pests.
They traveled the same distance and survived roughly as much as their wild counterparts did, in a ratio of two modified insects to one wild type, which was “remarkable” because in previous programs the ratio was much higher, Shelton said.
The GE moths also competed equally to the wild moths for female mates. However, wild female moths that mate with GE moths will not produce viable offspring – the self-limiting gene passed to offspring prevents them from surviving, leading the authors to conclude that with ongoing releases, pests can be suppressed in a targeted, sustainable way without using insecticides.
The GE moths would eventually have no one to mate with, which means they would decline as well and disappear from the environment within a few generations, the authors said. More releases would be needed to continue to suppress wild populations.
Positives for crop protection
With a method that could largely reduce the amount of pests and insecticides needed to eradicate them, the “potential impact for the growers and producers of those crops is huge,” said Alton Sparks, an entomology professor in the University of Georgia’s College of Agriculture.
“If this works and can be implemented, it would make my job a lot easier for this one specific group of crops,” said Sparks. “I’ve been battling diamondback moths on … crops in South Texas and here [in Georgia] for 32 years.”
Shelton previously conducted greenhouse studies in which they had diamondback moths feeding on broccoli. They had similar findings regarding pest suppression and elimination, but they also had moths that were resistant to insecticides.
Though the field releases have been successful, the practice isn’t that common, as it’s only been used on a few insects.
“If the technology works, it has tremendous potential, but it’s a very small set of agriculture because diamondback moths only affect a very small group of crops,” Sparks said.
Concerns of environmental impacts
There have been programs funded by the Bill & Melinda Gates Foundation and the US Food and Drug Administration that are geared toward modifying insects to fight diseases and illnesses including the ZIka virus, malaria and dengue fever.
In 2016, the FDA cleared a modified mosquito developed by Oxitec for a field trial in Florida, saying that it hadn’t found any negative effect on human health or the environment.
Some of these programs have been successful: From 2013 to 2015, Oxitec released roughly 450,000 modified male mosquitoes, which reduced the overall population by about 90%.
However, modifying insects is controversial, as the long term effects are unknown.
Many experts agree that more studies are needed to determine the long term effects of genetically engineering insects and whether manipulating genes upsets natural ecological cycles.
As for concerns for human health, Shelton said that contrary to the effect of insecticides on human health and the environment, the upside for GE insects is that the process is species specific, as they’ll only mate with each other.
“So, it’s not going to affect pollinators,” Shelton said. “It’s not going to affect biological control organisms and it’s not going to affect human health.”
Additional, longer studies are needed to fully assess modified moths’ ability to suppress pests and reduce insecticide resistance.
“We all live in the age of genetics,” Shelton said. “Whether it be looking at your family tree or genetically engineering plants, we just know so much more about the genes in insects that we can now utilize this knowledge to control the pest populations in a much more environmentally friendly way and a much more sustainable way.”
