Most people are familiar with the concept of genetically engineering crops to help them fend off pests and disease. A UK-based research company, Oxitec, has turned the tables by developing a genetically engineered version of the diamondback moth, a tenacious pest that feasts on cruciferous brassica crops like cabbages and cauliflowers.
The diamondback moth, which some researchers believe originated in Europe, can now be found all across the globe, including the Americas, Europe, Southeast Asia, Australia, and New Zealand. When it comes to cruciferous plants, the bug is an undiscerning diner. Cruciferous crops include many vegetables that are part of human’s daily diets such as brussel sprouts, kale, and radishes. And diamondback moths cost farmers roughly $4 billion – $5 billion each year, according to current estimates.
It’s during the larval stage that diamondback moths affect their crop destruction and although the larvae are small in size, they pose strength in numbers, with some farmers seeing their entire fields decimated in a single weekend. An outbreak of diamondback moth larvae can be particularly devastating for seedlings, often leading to the disruption of normal head formation in broccoli, cauliflower, and cabbage. Some larvae hide in the cruciferous plants’ florets, causing an affected batch to be rejected by virtually every produce dealer.
Prior attempts at controlling diamondback moth’s population have involved a range of insecticides sprayed broadly onto food crops. Other methods that have been used on other pests, although not diamondback moths, include Sterile Insect Technique (SIT). This involves sterilizing male insects using radiation and releasing them to mate with female insects. After successive releases, the amount of offspring produced in each life cycle declines and the pest population falls along with the threat it poses to crops.
Used for over 50 years in various locations in the world, SIT has worked for some insect pests, like the new world screw worm in livestock, but also has some downsides. “There are a number of disadvantages to this technique. One being the fact that radiation damages the insects and reduces their effectiveness in the wild,” Dr. Neil Morrison recently told AgFunderNews. Morrison, who leads the diamondback moth project with Oxitec, believes that the company’s radiation-free method offers a safer and potentially more effective method to controlling these pests.
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“Our founder, based at Oxford University, was working on insect genetics at the time. He identified a research tool that may have utility in something like SIT that could provide solutions to some of its downsides,” says Morrison. “The core of this was really that the genetics could provide a self-limiting technology that avoids the need for radiation.”
What makes radiation a risk? In addition to making them sterile, zapping the insects with radiation introduces breaks into their DNA thereby reducing their viability. As a consequence, they are less effective at mating causing many of the treated moths to die off before they can mate with a female and prevent her from having viable offspring.
Oxitec’s cutting-edge method uses genetic engineering to create ‘sterile’ male moths. When released, the sterile males mate with females and prevent a new generation of diamondback moths from being born resulting in a reduction of the insect’s population over time. “With our genetic variant, our males carry a self-limiting gene. If you release enough of these males for a sustained period of time, you will reduce the number of females in the next generation,” says Morrison.
While this might sound a bit dramatic, the impact is actually very local and could never result in the extinction of the moth species, according to Morrison. This makes it very practical for agricultural use. “It would be practically impossible to wipe out all the moths,” he says. “Our approach only has an effect where we release the moths. They are a local control for farmers’ fields.”
Looking into the future, Morrison and Dr. Chris Creese, Oxitec’s communications manager, envision Oxitec’s GM moths playing an important role in an integrated pest management system. “In many ag sectors, bio control providers are contracted to provide predators and parasitoids for chemical pest management,” says Morrison. “Our approach isn’t all that different. The key is to produce the insects cheaply.”
“Flexibility is an important component,” says Creese. “You will need a program with a series of releases to get the population under control.” After Oxitec’s moth’s have done their duty, farmers will be able to address their fields using the same battery of tools available to them today, including pesticides.
As Creese notes, the moths can be used concomitantly with other forms of pest control as long as the tools don’t affect the GM moths after they are released. “Because they are not resistant to insecticides, the pesticide-resistant moths would survive, and the helpful moths would be taken out,” says Creese. “But you can easily stagger the release of moths and pesticide sprays as needed and integrate with other tools. This is already being done successfully with our mosquitoes. There are a lot of different ways you could apply this so farmers would have a lot of choices for how to best manage their fields.”
“You may be able to drive down the population and take a ‘sit and wait’ approach,” explains Creese. “Using traps, you can monitor the population and determine whether you need to do another release.” The traps to which Creese is referring will play an important role in continued test trials involving the moths.
“After we release our males into the field we put traps out as a farmer would to monitor crops and these traps randomly catch moths in the crops,” says Morrison. “Every few days we take the trap back into the lab and take a look at the moths.” Pending continued success, Morrison envisions monitoring the moths through automated traps. The traps would collect a certain number of moths, scan them to detect which ones bear the red marker, inserted into its DNA during the process, and transmit the data remotely to a lab. This information then indicates whether another release is necessary and, if so, how many moths it should include.
Oxitec’s diamondback moth project has graduated from highly-controlled laboratory trials to a test run in field cages in upstate New York this summer. Oxitec has also continued to run trials in the US and UK in which moths are released into greenhouses. At each step of the process, Oxitec must obtain a series of permits and approvals to move its trials from the lab to the field. “One of the goals of the field cage work this summer is to get more data on traits like reproductive rate and mating competitiveness,” says Creese. “These traits will feed into the population model to help finesse what the optimal number of moths will be at the beginning.”
As with any scientific experiment, there are risks. But the risks involved with genetically modified diamondback moths are low, according to Morrison and Creese. One of the first questions asked is whether the moths could cause any potential harm. “They are non-toxic,” says Morrison. “And so from that perspective it looks pretty low risk. With these moths, for example, we applied for regulatory approval to do trials in the U.S. and they assessed all possible risks and came away with a Finding Of No Significant Impact.”
What impact might these Diamondback moths have on other insects? Probably not much. “The fact that it relies on mating between a male moth and a female moth means its very specific to the target pest,” says Morrison. “Unlike other methods, like broad spectrum insecticides, you really are targeting that one single problem pest. It’s a bit like using a scalpel instead of a sledgehammer.” The more exacting approach that Oxitec’s moths offer is particularly important when it comes to preserving beneficial insects around agricultural centers. “It means that other insects in the local environment that may be useful to the farmer like pollinators are left unharmed.”
Diamondback moths aren’t Oxitec’s first foray into genetically-engineered pest control. The company found success using a similar strategy to control dengue-carrying mosquitoes in Brazil. The company has an application pending with the FDA seeking approval to conduct trials with the mosquitoes in Florida. Using the same self-limiting gene and color marker technology, Oxitec modified male mosquito DNA so that their offspring carry a gene that causes them to die before reaching maturity.
“Over 100 million Oxitec mosquitoes have been released in approved trials worldwide with no adverse effects on people or the environment,” says Creese. “In every trial, more than 90 percent of the pest dengue mosquitoes were reduced.”
The continued success with diamondback moths indicates that this technology could lead to many other applications involving pest control. “The technology is very scalable. One stream of our research is definitely this sophisticated genetics and the other is to actually innovate in insect mass production with a view to economic implementation of our approach,” says Morrison. Oxitec’s work with the dengue-carrying mosquitoes is its most advanced example of how genetically modified pests can be reared en masse. “We’ve had successful trials in Central, South America and the Caribbean. These have been getting gradually larger in scale as well as successfully suppressing populations of these mosquitoes.”
To reduce the cost of producing the GM mosquitoes, Oxitec has developed a way to distinguish between the males and females at the juvenile stage. “We’ve also been producing mosquitoes very cheaply,” says Morrison. “We are able to separate males and females very efficiently by size so that when it comes to releasing in the field we are releasing the males, which don’t bite.”
As with anything involving genetic engineering, some members of the public have expressed their concern over the consequences of altering a species’ DNA. “It’s great that people are being environmental stewards and asking about the environmental impacts,” says Creese. Both Morrison and Creese underscored the point that the moths are non-toxic, posing no dangers to predators who eat them in the wild.
Although some may interpret Oxitec’s genetically engineered moths as a step away from nature, Creese sees an entirely different point of view. “The fact is, this is an invasive species in most places around the world. The GM moths would help to restore the local ecosystem closer to what it was before,” says Creese. “We all need to work together to help farmers feed the world in a safe, sustainable, eco-friendly way. Farmers need the support of funders, scientists, governments, and the public.”
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