Could genetically-modified pests control themselves? New research aims to prove that yes, they can.

Image credits Mike Pennington.

The study, led by Anthony Shelton, a professor at Cornell University’s Department of Entomology, describes the creation and successful release of gene-edited diamondback moths into an open field setting in collaboration with British biotechnology company Oxitech.

Engineered for failure

“The diamondback moth is a global pest that costs $4-5 billion annually and has developed resistance to most insecticides, making it very difficult to manage,” says Dr Neil Morrison of Oxitec, the study’s corresponding author.

Diamondback moths (Plutella xylostella) is one of the main pests for crops in the brassica family which includes cauliflower, cabbage, broccoli, and canola. Certain populations of diamondback moths have shown very stubborn resistance to synthetic insecticides in many settings around the world (including Canada, Australia, the UK, the US, and China); under the right circumstances, their larvae can afflict entire crops, causing farmers to re-plow entire fields of (now-unmarketable) produce.

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In order to address the threat, the team describes how they genetically-engineered the species to make it fail. They implanted two genes — a “self-limiting gene and a marker gene” according to Morrison — into the insect’s genome. These genes are meant to be handed down between generations creating “self-limiting moths [that] are non-toxic and non-allergenic.”

The idea behind this approach is for genetically-engineered male moths to make their way into the wide world and sow their wild oats with wild females. They’ll pass on the self-limiting genes, which prevent the female caterpillars from developing normally (so they die off).

But that’s just the theory — the team needed to test this approach in practice. Thus, they became the first group in the world to trial open-field releases of genetically-engineered moths, employing a “mark-release-recapture” method which has been long-used to study insect movements. Their findings suggest that their work is both effective and sustainable as a pest regulation strategy in the long term.

“Our research builds on the sterile insect technique for managing insects that was developed back in the 1950s and celebrated by Rachel Carson in her book, Silent Spring,” says Shelton. “Using genetic engineering is simply a more efficient method to get to the same end.”

“Professor Shelton’s team in Cornell conducted releases of self-limiting male moths alongside non-modified male moths, from the centre of the trial field planted with cabbage,” Morrison adds. “Traps throughout the field were set to recapture a proportion of released moths and, because they were marked with coloured powders, we were able to track their dispersal and lifespan in the field.”

After release, the gene-edited males behaved similarly to their unmodified counterparts in terms of distance traveled and survival. In a lab setting, the team adds, they were just as competent as unmodified males in competing for females. A mathematical model employed by the team further suggests that modified males would be sufficient to control the species’ population without the need for additional insecticides, making it sustainable and eco-friendly. Oxitec is currently evaluating where their technique can be used for the most benefit, in order to organize follow-up studies.

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The use of self-limiting insects isn’t novel here — the approach is already in use on Aedes aegypti mosquitoes in Brazil, Panama and the Caribbean in a bid to control the spread of malaria.

The paper “First Field Release of a Genetically Engineered, Self-Limiting Agricultural Pest Insect: Evaluating Its Potential for Future Crop Protection” has been published in the journal Frontiers in Bioengineering and Biotechnology.