By Emily Unglesbee
DTN Staff Reporter
ROCKVILLE, Md. (DTN) -- Diamondback moths would do well to be wary of potential mates in the years to come.
Scientists recently completed the first successful field testing of a genetically modified (GM) "self-limiting" insect in the U.S., using this species. When the GM male diamondback moths are released and mate with wild female moths, they pass on a gene that causes all female offspring from the match to die in the early larval stages.
"As you release our male moths over a period of time, eventually the number of female offspring goes down in the next generation and the pest population declines," explained Neil Morrison, head of agriculture programs for Oxitec, the biotech company that developed the GM moth.
Don't feel too bad for the moths, which are a major global pest of brassica crops, earning them the moniker "cabbage moths."
"Diamondback moths cause a tremendous amount of damage globally, between $4 to $5 billion a year," noted Anthony Shelton, a Cornell insect ecologist who led the field testing in upstate New York. "And they have an amazing propensity to develop resistance against insecticides very, very quickly. There are populations resistant to every insecticide ever used against it." That includes Bt, since foliar Bt sprays are used against this pest in the horticultural industry.
The scientists are hopeful the GM insects can be the start of a new pest control toolkit for farmers of many different crops around the world, which could combat insecticide resistance and perhaps even Bt resistance.
Unlike a gene drive, where genes are introduced into a population to permanently alter the genetic make-up of an insect population, Oxitec's GM insects will not persist in the environment, since they are designed to die off.
"Because half of its offspring die, and no females can pass it on, the trait naturally declines in a population over time," Morrison said. Field and lab trials have shown that after just a few generations of no viable female offspring, the GM moths eventually vanish from the population, he said. "The desire is to reduce the damage to the crop by reducing insect population, not eliminate the species," Shelton noted.
Oxitec has also done lab and field testing with self-limiting mosquitoes, specifically Aedes aegypti -- the species that carries dangerous diseases such as Zika virus, yellow fever and dengue fever -- in South and Central America. The company is currently waiting on EPA approval of a self-limiting mosquito for testing in the U.S.
But its moth trials are farther along in the U.S., and Morrison is optimistic that farmers could see them in the commercial pest control market within the coming decade. That will take additional field tests and approval from regulatory agencies such as USDA's Animal and Plant Health Inspection Service (APHIS). So far, the field testing did not reveal any significant differences in behavior among GM and wild moths, nor did studies find any impacts on non-target species, Shelton said.
In earlier greenhouse trials at Cornell, scientists found that the GM moths could also lower insecticide resistance, since the released GM males contain no insecticide-resistant genes common in wild populations, Morrison said.
"The males introduce insecticide-susceptible genes out there into the population," he explained. "So as well as reducing the population, they're diluting resistance to insecticides and enhancing effectiveness of insecticides within a season."
Oxitec is working with other agricultural pests, such as fall armyworm and soybean looper, in South America. Bt resistance is a growing problem with fall armyworm, and laboratory studies at Cornell suggest the GM moths -- and other future self-limiting insects -- could slow that type of insect resistance, as well, Shelton said.
"When we introduced the genetically engineered male moths in the lab, it not only suppressed the population but it also lowered the frequency of Bt-resistant alleles in the population and brought back susceptibility to the population," Shelton said.
The recent field tests also showed that the moths are unlikely to stray too far from the field where they are released, a common concern among skeptics of GM insect development. More than 95% stayed within 35 meters of the release site, Shelton noted. "We've known this for a long time about diamondback moths. If they have good quality food and environment, they tend to stay there."
Even if the moths do catch a wind current and move to different fields, such as an organic field, the GM insects would die off after a few generations, he added.
Ultimately, Morrison hopes the GM moths and other future self-limiting insects could provide farmers with a novel mode of action to supplement current pesticides on the market.
"I think they might work best as part of an integrated pest management approach by taking advantage of the relative strengths of other tools, such as insecticides or biocontrol products," he said. "Our approach would be suited to work alongside them. It would be highly complementary and sustainable."
See the Cornell and Oxitec scientists' recent field testing work here: https://www.frontiersin.org/….
Emily Unglesbee can be reached at Emily.firstname.lastname@example.org
Follow her on Twitter @Emily_Unglesbee.
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