Updated May 30, 2017
What is diamondback moth (DBM)?
The diamondback moth, Plutella xylostella, is a major agricultural pest and invasive species in New York State, as well as other states and countries. The moths 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 2 weeks.
Why are diamondback moths a problem?
The diamondback moth is the world’s worst insect pest of brassica vegetable crops including cabbage, broccoli, cauliflower, kale, radish and many other crops – costing farmers $4-5 billion annually worldwide. The caterpillars chew on leaves and can kill young plants or make the older plant parts unmarketable.
This invasive pest most likely came from Europe, but is now found throughout the world, including New York State and other states that farm brassica vegetables and field crops.
Because of their short generation time and high fecundity, diamondback moth populations can increase rapidly in the field and are not usually sufficiently controlled by natural enemies or other non-insecticidal integrated pest management practices. Hence, New York growers, as well as growers throughout the world, typically spray their crops with insecticides to reduce injury caused by diamondback moth larvae.
Yet this has led to development of resistance to most synthetic and organic insecticides in the diamondback moth, so it is increasingly difficult to control this non-native species and crop damage is increasing worldwide.
There is also concern about pesticide residues on crops, worker safety, and potential hazards to the environment including loss of pollinators and reduced biodiversity.
Alternative insecticide-free methods of control are urgently needed to ensure safe and sustainable brassica crop production in New York and globally.
Who is Oxitec?
Oxitec is a wholly owned subsidiary of Intrexon Corporation with an international team of scientists developing novel ways to control insect pests that spread disease and damage crops. The company is headquartered in Oxford, UK, and uses a ‘self-limiting’ gene developed through modern biotechnology and advanced genetics. This approach leverages the natural reproductive instincts of male insects to find pest females to mate, resulting in reduction of the pest population. For more information on the process of developing self-limiting insects, see the website www.oxitec.com
Have there been outdoor releases of genetically engineered insects?
Regulated environmental releases of Oxitec’s genetically engineered (GE) self-limiting mosquitoes have taken place since 2009. Efficacy trials in urban environments in Brazil, Panama and the Cayman Islands have shown that this self-limiting approach has reduced the Aedes aegypti population by more than 90%. These trials have been published in peer-reviewed journals (see below).
The Oxitec approach is similar to the sterile insect technique (SIT) that has been used for decades to control the American screwworm, a pest of livestock in North America, as well as several species of fruit flies (Dyck et al. 2005). However, in these SIT programs the sterility is achieved through doses of radiation that often have deleterious effects on the released insects so its use on many species has been limited. In the case of Oxitec insects, the ‘self-limiting’ effect is achieved through genetic engineering, thus avoiding the use of harmful radiation.
Is there successfully completed diamondback moth research?
Yes, research on the Oxitec GE diamondback moth has proceeded in a stepwise manner where laboratory and greenhouse studies have been completed in the United Kingdom and United States prior to consideration of outdoor studies as the next logical step. The results demonstrated that the GE diamondback moth performed as expected and successfully reduced the population of the pest moths. An enclosed field cage study was conducted in the summer of 2015 at the Cornell New York State Agricultural Experiment Station in Geneva, NY. This experiment evaluated the performance of the moths under natural conditions inside the cages. The results indicated that the GE diamondback moths are able to perform well in field cage conditions, offering promise for future diamondback moth management. Based on an independent review of the 2015 data from the caged study, the team at Cornell has determined that, once the necessary federal and NY State regulatory permits are in place, that a small-scale field trial is the next logical step in the evaluation of the self-limiting diamondback moth approach.
Next steps for diamondback moth research?
Following successful field cage evaluations, the first limited field trials are being considered in the US. These will comprise small-scale field releases for scientific evaluation of the field biology of the GE diamondback moth, including their movement and lifespan in a trial cabbage field.
Is the proposed field study under regulatory control?
The Cornell University College of Agriculture and Life Sciences is committed to ensuring that the trial is conducted in compliance with all applicable Federal and State regulations, as well as internal University requirements for oversight on Biosafety. As part of the regulatory process, the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) Biotechnology Regulatory Services (BRS), prescribes specific conditions which must be adhered to in order to ensure the trial is conducted in compliance with federal law. Compliance verification activities are a routine part of the regulatory oversight activities of the BRS, and Oxitec and Cornell work together to ensure all activities are carried out consistent with prescribed conditions. On April 19, 2017, USDA’s Animal and Plant Health Inspection Service (APHIS) announced it would make available for public comment a draft Environmental Assessment (EA) prepared in connection with the permit application for the field release of genetically engineered (GE) diamondback moths. The draft EA was available for a 30-day public review and comment period, which ended on May 19, 2017.
The 2015 field cage trials were conducted under USDA-APHIS-BRS permit number 13-297-102r, which was issued following extensive evaluation of the proposed study by the USDA-APHIS-BRS regulators. This evaluation process, which involved a public comment period, concluded in publication of an Environmental Assessment (EA) and a Finding Of No Significant Impact (FONSI).
What about safety?
Human health considerations form a key part of the regulatory process that APHIS-USDA-BRS undertakes in evaluating any trial application. The proteins from the fluorescent marker gene and the self-limiting gene are the same across the Oxitec portfolio of self-limiting insect control products. Independent evaluation by the Food Allergy Research and Resource Program of the University of Nebraska–Lincoln of the toxic or allergenic potential of these proteins, known as DsRed2 (fluorescent marker) and tTAV (self-limiting gene) has been key to regulatory submissions for all Oxitec products to date. No toxic or allergenic potential has been identified. Additionally, the impacts on non-target organisms through oral exposure of GE insects carrying the DsRed2 and tTAV proteins have been evaluated through direct feeding studies, consistent with international guidelines, involving predatory insects as well as guppy fish, and no adverse impacts were observed even when fed an artificially high diet of 100% GE insects (e.g. Nordin et al. 2013).
How does the self-limiting approach work?
Oxitec male moths pass on a self-limiting gene that prevents their female offspring from reaching adulthood. This reduces the number of females able to reproduce, and so with repeated releases of Oxitec’s male moths, the pest population in the release area shrinks. This method is self-limiting and does not persist in the environment, unlike gene drive approaches, which are designed to persist in the environment long term.
What about environmental impacts?
Unlike conventional insecticides that can have off-target effects, the self-limiting approach by mating is species-specific, impacting only the intended pest diamondback moth population. This is because the released GE diamondback moths will only mate with their own species, producing offspring which carry the self-limiting gene.
The open field trials will be limited to the area of the test crucifer fields at our research station and, based on previous studies, these insects are unlikely to travel far from the ample food available to them at the test field. Adult diamondback moths have a short life span in the field, typically living for less than a week. Data available from tests of the proteins produced by the GE diamondback moths for toxicity and allergens show they are non-toxic and non-allergenic. Oxitec has also conducted or commissioned feeding studies in a variety of non-target organisms such as spiders, rove beetles, fish and parasitoids, all using insects carrying the same introduced genes as the GE diamondback moths as the feed source. In all cases no adverse effects were observed. Thus, if predators–or even people–ingest a modified moth, it would be no different than ingesting a pest diamondback moth. The test field will be insecticide-treated after the study, and the moths and the crop will be destroyed and will not enter the food or feed chain.
The potential environmental consequences of the GE diamondback moth release are rigorously evaluated as part of the USDA application process. In a previous application for the GE diamondback moth release, under which the 2015 caged trials were conducted, the USDA issued a comprehensive “Finding of No Significant Impact” statement which concluded that the release should be permitted. The decision was based on a rigorous evaluation of environmental considerations including plant communities, wildlife and biodiversity, among other elements.
Should there be local concerns outside of the experimental field?
Releases of adults will be made in the middle of a large circular field of cabbage, and their movement patterns will be assessed. Our previous studies have indicated that diamondback moths tend not to travel far in the presence of a host crop. Approval from the appropriate regulatory bodies will be based on the safety of the GE diamondback moth, the isolated field, the topography of the experimental field and its surroundings and the short lifespan of adults.
Can organic growers use this technology?
Although organic growers use fertilizers and pesticides, they are prohibited from using any product that is synthesized, including fertilizers and pesticides. Therefore, they cannot utilize GE insects.
Who benefits from this research?
Using GE diamondback moths provides a means of species-specific control over this invasive pest, thereby reducing the crop damage caused by diamondback moth larvae. Currently, New York growers, as well as growers throughout the world, typically spray their crops with insecticides to control diamondback moth (Talekar & Shelton 1993). However, 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. By controlling diamondback moth and decreasing reliance on insecticides, new technologies such as the GE diamondback moth will bring local and global benefits from improved food security, food safety, and environmental protection.
Insects are becoming increasingly important to control for both the benefit of agriculture and human health, and there is a pressing need for new technologies to be developed. Growers in New York and worldwide are faced with an expanding list of new invasive pests (e.g. spotted wing Drosophila) for which novel and safer technologies, including genetic engineering, are needed. Scientists and administrators at Cornell are poised to be leaders in ensuring research on these new technologies is conducted in a safe, transparent and properly regulated matter.
Who funds this work?
Oxitec, the company that developed GE DBM, is paying the cost to conduct this research project. However, as with all outside-funded projects at Cornell, Oxitec has no influence over the outcome of the trials or publication of results. This is clearly stated in Cornell’s Faculty Handbook. Neither Professor Shelton nor anyone in his program will receive financial benefits from this work. Upon completion of this study, a report of the study will be submitted to a peer-reviewed journal and made available to the general public.
Where can I get additional information?
- Cornell site: http://shelton.entomology.cornell.edu
- Oxitec site: www.oxitec.com/dbm and email: firstname.lastname@example.org
- Final Environmental Assessment issued by USDA as part of permit for 2015 trials (http://www.aphis.usda.gov/brs/aphisdocs/13_297102r_fea.pdf)
- Finding Of No Significant Impact issued by USDA as part of permit for 2015 trials (http://www.aphis.usda.gov/brs/aphisdocs/13_297102r_fonsi.pdf)
- Nordin et al. 2013. Oral ingestion of transgenic RIDL Ae. aegypti larvae has no negative effect on two predator Toxorhynchites species. PLoS One 8: e58805 http://www.ncbi.nlm.nih.gov/pubmed/23527029
- More information on diamondback moth can be seen at http://web.entomology.cornell.edu/shelton/diamondback-moth/index.html
- Carvalho et al. (2015). Suppression of a field population of Aedes aegypti in Brazil by sustained release of transgenic male mosquitoes. PLoS Negl Trop Dis 9(7) DOI.org/10.1371/journal.pntd.0003864
- Harris et al. (2011). Field performance of engineered male mosquitoes. Nature Biotechnology, 29, 1034-1037. DOI 10.1038/nbt.2019
- Harris et al. (2012). Successful suppression of a field mosquito population by sustained release of engineered male mosquitoes. Nature Biotechnology, 30, 828-830. DOI 10.1038/nbt.2350
- Gorman et al. (2015). Short-term suppression of Aedes aegypti using genetic control does not facilitate Aedes albopictus. Pest Management Science, 72, 618-628. DOI 10.1002/ps.4151
- Talekar, N.S. & Shelton, A.M. 1993. Biology, ecology and management of the diamondback moth. Annual Reviews of Entomology, 38, 275-301.
- Sterile Insect Techniques: Principles and Practices in Area-Wide Integrated Pest Management (2005). V.A. Dyck, J. Henrichs and A.S. Robinson. Springer. http://www-naweb.iaea.org/Nafa/ipc/public/Sterile_Insect_Technique_book.pdf#page=14