Researchers Genetically Engineer Insects To Turn Against Themselves
Want to crash an insect population? Slip in a self-limiting gene and topple the family tree in two to three generations. The promise of biotech mosquitoes to combat the pest that spreads Zika, dengue and yellow fever grabs the headlines, but the same technology using genetically engineered (GE) insects is being studied on U.S. farmland.
The arrival of GE insects in agriculture could usher in a new wave of pest management and result in a significant reduction in broad-spectrum insecticide applications. With the flick of a genetic switch, agriculture could turn the sex drive of an insect against itself.
A cabbage field in west-central New York serves as U.S. agriculture’s ground zero of GE insect research. Anthony Shelton, Cornell University professor of entomology and renowned expert on insect pest management, is using biotechnology to place GE crosshairs on a remarkably adaptable crop pest: diamondback moth (DBM).
In the pantheon of devastating pests, DBM casts a long shadow across global farmland as a major killer of broccoli, cabbage, canola, cauliflower and more, racking up $5 billion per year in damage. A consummate survivalist, DBM features a remarkable ability to develop resistance to insecticides (sometimes within two years) by reproducing a generation within a few weeks in the field. DBM has developed resistance to every insecticide class used against it, according to Shelton: “It’s a leader in the resistance movement and is the first insect to have developed resistance to Bt.”
Shelton is using technology developed by Oxitec to target DBM. Oxitec, at the vanguard of GE insect research and technology, has garnered attention through its releases of GE male mosquitoes in Brazil and other countries.
When Shelton releases DBM males modified by Oxitec, they mate with wild females. Through biotech engineering, all female offspring die as a result of a self-limiting gene. With the continued release of male moths over a sustained period, the number of females in the population drops, and the capacity of the population to sustain itself is diminished.
Typical insecticide resistance isn’t an issue because the developed strain is susceptible to insecticides and as the insects die, the potential build-up of insecticide resistance genes is blocked. Could behavioral resistance develop? “In theory, wild insects could evolve a preference strictly for other wild insects,” Shelton says. “We have to look for that, but we have seen no indication so far.”
Reduced Populations. GE insect technology essentially uses biotech sterilization. Current insect sterilization methods, such as sterile insect technique (SIT), use radiation. Developed in the 1950s, SIT targeted the screw-worm, which annually inflicted heavy losses on the cattle industry. SIT was highly successful in controlling screw-worm, several fruit flies, pink bollworm and more.
In 1990, Shelton was asked by the International Atomic Energy Agency to work on a SIT project to sterilize DBM with radiation in Indonesia and Malaysia. The radiation dose sterilized the moths, but they didn’t hold up well to the treatment and weren’t fit enough to fly and mate. The project was dropped due to the limits of radiation. Rather than the sledgehammer of radiation, current GE insect technology is akin to precision surgery.
In 2015, Shelton and his colleagues completed GE DBM greenhouse trials proving the technology was effective—the pest DBM population crashed after several releases of GE DBM. The trial also restored susceptibility to Bt. In fall 2017, he completed open-field testing to assess the behavior of GE DBM.
“Growers need tools and this one is species-specific. There are so many concerns about the broad-spectrum effect of some insecticides on pollinators,” he notes. “If something as benign as genetic engineering helps control insects, growers will want to adopt this technology.”
At The Source. Shelton also touts the potential for using biotechnology in diverse ways to help manage pests. Current discussion usually centers on the development of GE crops resistant to particular insects, but Shelton believes the focus also could be placed directly on engineering pests to control themselves.
“In so many cases, maybe a more effective way of using biotech is to engineer the pest to take care of itself,” he says. “We’ve got GE crops of all types, but let’s think about GE insects to supplement, or in some cases replace, those crops.”
Are all agricultural insect pests a candidate for GE control? “The top consideration is whether they reproduce sexually,” says Neil Morrison, research lead for agricultural pest control at Oxitec. “That leaves most pests still on the table. Our technology is highly suitable for a whole lot of important pests.”
GE technology used with DBM has an additional benefit to direct pest suppression, in that male progeny initially survive. “If our factory colony is insecticide susceptible, those susceptibility genes are pushed out into the pest population,” Morrison explains. “We’ve done laboratory tests indicating this could have a powerful resistance dilution effect. We potentially have a powerful tool for managing insect resistance to insecticides in biotech crops.”
Timelines depend on the regulatory process, but Morrison expects some GE insect use within a decade. Navigating EPA requirements for GE insects is a trip into uncharted waters. “Given the nature of our solution, the success of Oxitec relies on partnerships with each country,” says Sarah Hoey, communications manager at Oxitec. “Working closely with collaborators around the world, we’re able to develop the best strategy for each location.”
This technology may strike an important balance. “This technology is one of the most sustainable means of pest control, period, and it has a lot to offer growers and the environment,” Morrison adds.