Genetically Engineered Male Moths Released into Wild to Wipe Out Females

Scientists have released male moths genetically engineered with a destruct gene into the wild to wipe out females. They say is the first open-field release of a self-limiting diamondback moth.

The study's authors describe it as "an exciting next step" and "a promising future option" when it comes to protecting crops against pests.

The study, published in Frontiers, used male diamondback moths (or Plutella xylostella), whose DNA had been tweaked with a self-limiting gene. When this gene is passed onto female offspring, it prevents the caterpillar from surviving into adulthood and thus, from reproducing.

To test the effectiveness of this method, the scientists used a series of experiments in the field and in the laboratory.

The open-field experiment involved the "mark-release-recapture" technique⁠—researchers dusted two strains of moth (modified and non-modified) with a fluorescent powder before releasing the insects into a cabbage field, where their movements and behavior could be monitored.

Complimentary laboratory experiments confirmed there were no significant differences between genetically modified and non-genetically modified strains of moth in terms of growth rates and mating competitiveness.

The researchers plugged the results from these experiments into mathematical models. This allowed them to work out how the rate at which genetically modified males are released into target moth populations affects suppression.

The study's authors say there is strong evidence to suggest genetically modified moths can be used to manage pest populations. Once the the release of genetically modified insects stop, numbers of affected insects drop and are gone from the ecosystem within a few generations.

Cabbage Farm
The diamondback moth feeds off brassica crops like cabbage and costs the world billions in crop damage each year. Genetically modified males could be the answer, say researchers. Picture: Tractors are idle in a field of cabbage while the farm workers take a lunch break on January 30, 2016 in Los Alamos, California.

The benefit of using genetic engineering over pesticides is that it is "species-specific," lead author Professor Anthony M. Shelton in the Department of Entomology at Cornell University told Newsweek.

Beneficial organisms like pollinators can get caught up as collateral damage in indiscriminate chemical forms of control but are unaffected by this new technique.

"The field study is an exciting next step in demonstrating that self-limiting diamondback moths can show strong performance under field conditions," Shelton added. "With the results indicating that this biological approach is a promising future option for farmers to protect their food crops from this damaging pest, which is notorious for developing resistance to insecticides."

The damage wrecked by diamondback moths cost the global economy an estimated $4-5 billion every year. Worldwide, the combined cost of agricultural crops lost due to arthropod pests like aphids and spider mites add up to more than $470 billion.

Pesticides are the leading method for protecting crops against this kind of damage and costs huge sums. The worldwide cost is projected to reach $16.44 billion by 2019.

One of the problems with these more traditional forms of pest control is that it kills indiscriminately, damaging pollinators just as much as it does pests. Some studies have found that over 40 percent of bee colonies are lost in the U.S. each year due to a number of factors that include pesticides. There is also the growing problem of resistance. At least 586 insect species are resistant to one or more pesticides, including the diamondback moth.

"It's encouraging to see the development of genetic control techniques for a globally-significant crop pest reach the stage of open-field testing," Dr. Callum MacGregor, an entomologist and ecologist at the U.K.'s University of York, told Newsweek.

"Pest-control techniques such as this, which target a single species via an artificially-introduced female-killing gene, carry virtually no risk to non-target species or even to the long-term persistence of wild populations of the target species."

However, there is more research that needs to be done to assess its full impact on existing ecosystems.

"Some impacts on non-target species could occur through changes in food webs as a result of successful diamondback moth suppression, for example through increased predation of non-target species by the predators of diamondback moths," said MacGregor. "The present study did not assess these ecosystem-scale impacts of their releases, so this will be an important question for future study."

There are already plans to extend this self-limiting approach to target pests like the fall armyworm, larvae of the armyworm moth native to the tropical and subtropical Americas.

According to the Food and Agriculture Organization of the United Nations (FAO), it was first detected in Central and Western Africa in 2016 and has since spread through Sub-Saharan Africa. The pest has now been confirmed across Asia, from Yemen to Japan.

Similar approaches have been used to target disease-carrying insects like the Aedes aegypti, which can carry dengue, zika, chikungunya and yellow fever.