Diamondback moth

Diamondback moth (Plutella xylostella) is the biggest global pest of brassica crops

Why we need a solution to the diamondback moth pest

The diamondback moth (DBM) is one of the world’s significant agricultural pests, costing farmers billions of dollars every year. This moth pest, also called Plutella xylostella, is a non-native species in the USA. It feeds on brassica crops like canola (oilseed) and broccoli and it is notorious for its ability to develop resistance to insecticides. This means that new methods of pest control are needed that are both effective and environmentally friendly.

Benefits of Oxitec’s approach

Oxitec is an award-winning pioneer in insect pest control with an approach that is both effective and environmentally friendly. We genetically engineer insects to use them as a tool to control populations of their own species.

Studies in the lab and greenhouse cages have shown that Oxitec DBM can be very effective at reducing pest DBM populations. For example in cage studies the pest populations were effectively controlled within 8 weeks.

beneficial insect

The approach is toxin-free and does not target beneficial predators or insects.

The male moths only mate with their own species so the genes don’t spread. And the insects die out so the released insects and their genes do not persist in the environment.

Reducing reliance on insecticides will help beneficial insects, like bees, to thrive.

For a recent study on control of the diamondback moth pest using the Oxitec moth click here.

How the Oxitec Diamondback Moth (OX4319L) works 

Oxitec male moths are released to mate with female moths of their own species. They pass on a ‘self-limiting’ gene that prevents the female offspring from reaching adulthood. This reduces the number of reproductive females and the pest population in the release area shrinks. The Oxitec DBM also have a fluorescent marker (DsRed2) to identify the Oxitec moths and distinguish them from wild ones. This colour marker is used to monitor control of the pest population.

Next steps

The Oxitec DBM has been evaluated in lab and greenhouse studies in the UK and US and is now ready for further evaluation in field trials. The first field trials are planned in the US and approval for such a trial has been approved by the Animal and Plant Health Inspection Service (APHIS) Biotechnology Regulatory Services, a part of the US Department of Agriculture (USDA), following extensive review. This regulatory review has also included a public consultation process. Field cage studies were conducted in the summer of 2015, and data analysis is under way. We are planning to conduct further field trials in the summer of 2016.





What is diamondback moth (DBM)?

The diamondback moth, Plutella xylostella, is a major agricultural pest and invasive species in New York State and across the US – they are small, about the length of two grains of rice, but females can lay upwards of 150 eggs during their lifetime and a generation can be produced in as little as two weeks.

Why is DBM a problem?

DBM is the world’s worst insect pest of brassica vegetable crops such as cabbage, canola, broccoli, cauliflower, and kale – costing farmers $4-5 billion annually worldwide.

This invasive pest probably came from Europe, but is now found throughout the world, including New York State and other states that farm brassica vegetables.

This moth rapidly grows large populations and is not sufficiently controlled by natural enemies or other integrated pest management practices. Hence, frequent use of insecticides is the common practice, and New York growers, as well as growers throughout the world, typically spray their crops with insecticides to reduce injury caused by DBM larvae.

But this has led to development of resistance to most insecticides in DBM, so it is increasingly difficult to control this non-native species and crop damage is increasing worldwide.

There is also growing concern about pesticide residues on crops, worker safety, and potential hazards to the environment.

Alternative insecticide-free methods of control are urgently needed to ensure safe and sustainable brassica crop production globally.

What are potential solutions?

To help farmers control the DBM problem, we need to reduce our reliance on pesticides by integrating pest control methods with new tools. Twin goals for scientists and farmers are to find new pest control methods that are both effective and environmentally friendly.

Genetically engineered (GE) DBM is one potential solution, which has been developed by Oxitec.

Who is Oxitec?

Oxitec is a spinout company from Oxford University with an international team of scientists developing safe and environmentally friendly ways to control insect pests that spread disease and damage crops. The company is headquartered in Oxford, UK where it has a dedicated team of 45 people. What they do is leverage the natural reproductive instincts of male insects to find pest females to mate. These benign males are genetically engineered so their offspring die prematurely, and this reduces the pest population in a way that is non-toxic and pesticide-free. This approach is species-specific so other insects and predators are not affected, and it is self-limiting so the insects and their genes do not persist in the environment.

How does genetically engineered insect control work?

Oxitec insects are genetically engineered so their female offspring die before they can reproduce on crops and before they can become transmitters of disease. It’s an approach similar to the Sterile Insect Technique (SIT) where male insects are sterilised by radiation and released to mate with pest females. With successive releases there are fewer offspring each generation and the pest population crashes. SIT has been used worldwide for more than 50 years and has been successful in tackling pests such as New World Screwworm, a major pest of cattle and other livestock.

The Oxitec DBM is inspired by the SIT approach but doesn’t rely on radiation, which can affect many genes and the insect’s competitiveness. Instead, Oxitec uses just one gene to induce ‘sterility’ and a color marker gene for monitoring the results. Like SIT, this approach requires successive releases, but there are major environmental benefits such as the fact that after releases are stopped, the insects and their genes not persist in the environment. The approach is also species-specific, controlling only the non-native DBM so other native species and beneficial insects such as bees can thrive.

Have there been outdoor releases of genetically engineered insects?

Yes, genetically engineered pink bollworm has been released in the US in Arizona by the USDA since 2006 as part of their SIT program to control this major pest of cotton.

Field trials using genetically engineered mosquitoes to control their own species have been taking place since 2009, with more than 90 million modified mosquitoes released worldwide to control Aedes aegypti, a non-native mosquito species that spreads serious diseases such as dengue, chikungunya and zika virus. In every trial, Oxitec has reduced target Ae. aegypti populations by more than 90%, which is an unprecedented level of control (world-leading mosquito control groups using best available methods can only reduce the Ae. aegypti population by up to 50%, which is not enough to prevent the spread of disease). Field trials have taken place in Cayman, Brazil, and Panama and more are being planned.

Is there successfully completed DBM research?

Yes, research on genetically engineered insects proceeds in a stepwise manner and this is the case for GE DBM, where lab and greenhouse studies have already been completed in the UK and US. The first scientific investigations were laboratory evaluations of the moth strain. Following those studies, releases of GE DBM were evaluated in contained glasshouses. The results demonstrated that the GE moths performed as expected and successfully reduced the population of the pest moths. The next step for evaluation is small-scale field trials.

Next steps for DBM research?

The first field trials are being planned in the US. An enclosed field cage study is planned for summer 2015 at the Cornell New York State Agricultural Experiment Station in Geneva, NY. This will evaluate the performance of the moths under outdoor conditions inside the cages. Following the successful completion of that research, the next step would be a small-scale field release for scientific evaluation.

Is the field study under regulatory control?

Yes, this is a research program regulated at Federal, State and university levels. This included a regulatory review by independent experts to obtain a permit for field trials, and there is an on-going monitoring process for the project. Following extensive evaluation of the GE DBM and proposed study, the Animal and Plant Health Inspection Service (APHIS) Biotechnology Regulatory Services (BRS), a part of the US Department of Agriculture (USDA), published an Environmental Assessment (EA) and conducted a Public Consultation. The notification was published in the Federal Register, and the process included review by the public and a public comment period. It is worth noting that the public comments did not register any specific factual concerns with the data provided in the EA.

There were no identified risks to human safety or the environment, and following the public review, APHIS approved the field trial and published a Final EA and Finding Of No Significant Impact (FONSI).

All APHIS-BRS regulated trials are issued with requirements for compliance. It is a legal responsibility to undertake these compliance actions and in the case of the DBM field trials, this includes spraying with insecticide at the end of the trial of both the trial plot and a 100m radius of treated fields after the removal of DBM, post-trial monitoring for a specified period after the last release, and destruction of the experimental brassica plants used in the study as they will not enter the food or feed chain.

A monitoring and compliance plan has been drawn up and will be enacted following further discussion with the BRS compliance group. The New York State Department of Environmental Conservation (DEC) have also approved the cage trial this summer.

What about safety?

The GE DBM are no different to wild ones except that they have a color marker to track and trace them in the environment and they cannot reproduce effectively – this suppression of reproduction is what controls the pest population that damages crops.

The proteins from the color marker gene and self-limiting gene that causes female offspring to die prematurely before they can reproduce are non-toxic and non-allergenic.

APHIS-USDA evaluated the GE moth for safety to humans and the environment and the field trials would not have been approved if there were safety issues.

What about environmental impacts?

Because the proteins of the color marker and self-limiting gene are non-toxic and non-allergenic, if predators ate GE DBM, it would be no different from eating a wild one. Predator feeding studies using genetically engineered insects with these genes show there is no impact, even when fed an artificially high diet of 100% GE insects (eg, Nordin et al. 2013). Oxitec has conducted or commissioned feeding studies in a variety of non-target organisms such as spiders, rove beetles, fish and specific parasitoids, all using insects carrying the same genes as the DBM. In all cases no adverse effects were observed.

Unlike insecticides that can affect other species vulnerable to them, this method of pest control is species-specific. And the genes do not spread.

Reducing reliance on insecticides by using other methods will help to reduce pesticide residues on foods, combat insecticide resistance, control an invasive species, and protect other species and the environment.

APHIS-USDA evaluated the GE moth for environmental impacts before approving the field trials.

Would organic farmers near the study site lose their organic certification?

According to the USDA, any unintentional presence of residue from a genetically engineered organism does not affect organic certification.

As far as we are aware no organic farmer in the US has lost organic certification because of trace presence of GMOs due to proximity to a farm or field trial using GMOs. And there are 70 million hectares of GM crops in the US.

It’s worth noting that we are far from a hypothetical situation of genetically engineered DBM being used as a commercially available tool in fields to control this invasive and destructive agricultural pest. This is a scientific investigation of a research strain under controlled conditions in accordance with the regulatory permit.

An important distinction here is that the issue of GM crop ‘contamination’ of organic crops is due to the possibility that a modified plant trait could be adopted by the organic plant population. This is not the case with GM insects as the genes do not spread to the crops or other organisms. The genetic control of the pest insect is species-specific and self-limiting, and the insects and their genes do not persist in the environment.

The fact is that some research strains go ahead and others do not. Our purpose is to find environmentally friendly and effective pest control options for farmers. For that to happen the science must take place to honestly evaluate these tools.

Who benefits from this research?

There are local and global benefits from improved food security, food safety, and environmental protection. New York growers, as well as growers throughout the world, typically spray their crops with insecticides to reduce injury caused by DBM larvae. This has led to the insect developing resistance to most insecticides and increased levels of crop damage, as well as increased concerns about worker safety, pesticide residues on crops, and potential hazards to the environment. Using GE DBM does not have these drawbacks because they control just this invasive pest. Such species-specific control and a reduced reliance on insecticides can help protect other beneficial organisms such as pollinators. Growers urgently need better alternatives to conventional and organic pesticides, and reducing DBM-crop damage in a sustainable way will help to improve food security in the US and worldwide.

Where can I get additional information?

You can get in touch directly dbmtrial@oxitec.com

1. Cornell site: http://shelton.entomology.cornell.edu

2. Oxitec site: www.oxitec.com/dbm

3. Proposal to USDA for the release, May 2014 (http://www.aphis.usda.gov/brs/aphisdocs/13_297102r_dea.pdf)

4. Federal Register / Vol. 79, No. 167 / Thursday, August 28, 2014 / Notices (http://www.aphis.usda.gov/brs/fedregister/BRS_20140828b.pdf)

5. Final Environmental Assessment (http://www.aphis.usda.gov/brs/aphisdocs/13_297102r_fea.pdf)

6. Finding Of No Significant Impact (http://www.aphis.usda.gov/brs/aphisdocs/13_297102r_fonsi.pdf)

7. Nordin et al. 2013. http://www.ncbi.nlm.nih.gov/pubmed/23527029

8. More information on DBM can be seen at  http://web.entomology.cornell.edu/shelton/diamondback-moth/index.html and http://shelton.entomology.cornell.edu/2015/06/17/cornell-dbm-project-2015/