The Mediterranean fruit fly (Ceratitis capitata), or medfly, is one of the world’s most destructive agricultural pests.
Western Australia’s Department of Agriculture and Food (DAFWA) have announced they will trial the Oxitec medfly in glasshouse studies slated to begin next year. For more information on their trial go to www.agric.wa.gov.au/fruit-fly-trial-western-australia
Why we need a solution to the Mediterranean fruit fly pest
The Mediterranean fruit fly (Medfly, Ceratitis capitata) is a major problem for commercial orchards and householders alike, attacking more than 250 types of fruits, including citrus, apricots, nectarines, peaches, mangoes, apples and pears. The female medfly ‘stings’ fruits as she lays her eggs, making them vulnerable to infection and rot. Medfly’s versatility in the variety of crops it targets means that it is a pervasive threat all year round that requires intense insecticide control to prevent infestation. In Australia and the Americas it is also an invasive pest.
The medfly is difficult to control by conventional methods, so new methods of pest control are needed that are both effective and environmentally friendly.
Challenges with current control methods
Traditionally medfly has been controlled by the application of insecticides. – In some places this has been achieved through orchard hygeine and by spraying orchards and treating fruit post-harvest with insecticides. Recently two key insecticides for medfly management – dimethoate and fenthion – were suspended by Australian authorities. This has left growers with fewer tools to protect their fruit crops against the medfly pest, so new options are needed, especially those that can be part of an Intergrated Pest Manamgent (IPM) approach for more environmentally friendly and sustainable agriculture.
The Department of Agriculture and Food in Western Australia (DAFWA) are currently investigating options for new and improved control of medfly. One such approach is the Sterile Insect Technique (SIT) where insects are sterilised by radiation prior to release over orchards. By mating with pest females, they reduce the number of pest flies in the next generation. Oxitec’s approach is a type of SIT that uses a self-limiting gene instead of radiation to reduce the number of pest offspring.
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 laboratory and greenhouse cages have shown that Oxitec medfly can be very effective at reducing pest medfly populations. For example, in cage studies the pest populations were effectively controlled within 12 weeks.1
The approach is toxin-free and does not harm beneficial predators or insects.
The male flies only mate with their own species so other species are not directly affected. Also as this approach is based on preventing reproduction it is self-limiting in the environment
Reducing reliance on insecticides will support more sustainable agriculture and help beneficial insects, like bees, to thrive.
How the Oxitec Medfly (OX3864A) works
Oxitec male flies are released to mate with female flies of their own species. They pass on a ‘self-limiting’ gene that prevents the female offspring from reaching adulthood so they cannot ‘sting’ fruit crops or reproduce. This shrinks the pest population in the release area. The Oxitec medflies also have a fluorescent marker (DsRed2) to distinguish the Oxitec flies from the pests. This colour marker is used to monitor control of the pest population.
The Oxitec Medfly has been evaluated in laboratory and greenhouse studies in the UK, Austria, Greece and Brazil.
Oxitec medfly has also been approved for outdoor trials in Brazil.
In Australia, DAFWA are planning a glasshouse evaluation of Oxitec medfly to evaluate how easily they can be produced and how well Australian female pest medflies mate with Oxitec males. For more information on this trial see www.agric.wa.gov.au/fruit-fly-trial-western-australia
What is the Mediterranean fruit fly (medfly)?
The Mediterranean fruit fly (Ceratitis capitata), or medfly, is one of the world’s most destructive agricultural pests. The female medfly injects her eggs into ripening fruit so that the larvae can feed on the soft pulp. Bacteria and fungi enter through the hole and cause the fruit to rot. The medfly originated in sub-Saharan Africa and is invasive, spreading to almost all tropical and subtropical areas of the world. It can infest over 250 different hosts.
The life-cycle of these flies (egg-to-reproducing adult) can be as short as 21 days in ideal conditions and adult medflies typically survive three months.
Why is medfly a problem?
Medfly is one of the world’s most devastating insect pests for growers.
This pest fruit fly originates in part of Sub-Saharan Africa, and is a non-native species in most of its range in tropical and sub-tropical parts of the World.
Growers currently use several tools to try to minimise damage by Medfly, including insecticides and the sterile insect technique (SIT). There is also growing public concern about insecticide residues on crops, worker safety, and potential hazards to the environment. Alternative methods of control are urgently needed to ensure safe and sustainable fruit production globally.
What are the potential solutions?
To help growers control medfly, new tools are needed as pesticides are being phased out. Twin goals for scientists and growers are to find new pest control methods that are both effective and environmentally friendly.
Genetically engineered (GE) medfly is one potential solution, which has been developed by Oxitec.
For more information on current control measures in Western Australia see DAFWA’s medfly control website http://agspsrv34.agric.wa.gov.au/Ento/medfly.htm
Who is Oxitec?
Oxitec is a spinout company from Oxford University and subsidiary of Intrexon (NYSE: XON), 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 about 60 people. Oxitec harnesses the natural reproductive instincts of male insects to find pest females to mate.
The Oxitec male insects 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 the food-chain are not affected, and it is self-limiting so the insects and their genes do not stay in the environment.
How does genetically engineered insect control work?
Oxitec medfly is genetically engineered so their female offspring die before they can reproduce on crops. It is 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 SIT approach is also used against the medfly, but this method faces a number of challenges. For instance, sterilising flies with radiation can weaken them so they are less successful at mating pest females and this can require higher numbers of released flies. Facilities for production and radiation can also be expensive, and marking released flies for monitoring in the field can be difficult and unreliable.
The Oxitec medfly is an update of the conventional SIT approach, but does not rely on radiation sterilisation. Instead, Oxitec uses a highly targeted genetic approach. The pest flies have a self-limiting gene and so cannot reproduce effectively, and a fluorescent marker gene is used for monitoring the results. Like SIT, this approach requires successive releases during which the medfly population is controlled.
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 Oxitec mosquitoes have been taking place since 2009, to control Aedes aegypti, a non-native mosquito species that spreads serious diseases such as Dengue, Chikungunya and Zika virus. In every suppression trial, Oxitec has reduced the dengue mosquito population by more than 90%, which is an unprecedented level of control. Field trials have taken place in Cayman, Brazil, and Panama and more are being planned.
What research has been completed to date on Oxitec medfly?
For Oxitec medfly, laboratory studies have already been completed in the UK, Austria and Greece. Following those studies, GE medfly were evaluated in contained glasshouses. The results demonstrated that the GE medfly performed as expected and successfully reduced the population of the pest flies. Now Oxitec medfly has gained regulatory approvals for glasshouse studies in Australia and for outdoor trials in Brazil.
What are the safety considerations?
Before any genetically engineered insect is imported or evaluated in a laboratory or other environment a detailed and independent regulatory process takes place. – Indoor or outdoor evaluations can only proceed following review by independent experts as part of the regulatory approval process.
Apart from the inability to reproduce effectively, the Oxitec medflies are no different to wild ones except that they have a fluorescent marker to identify them in the environment. This distinguishes them from the pest flies and provides a unique monitoring capability.
The proteins produced by the colour marker gene and self-limiting gene, are non-toxic and non-allergenic.
This system is similar to the Oxitec mosquito where more than 100 million Oxitec mosquitoes have been released worldwide, using the same self-limiting approach, with no reports of adverse effects on people or the environment.
What are the environmental considerations?
Potential environmental impact is a key part of regulatory assessments that must be carried out prior to any regulatory approval.
Unlike insecticides which can affect a broad variety of insect life including bees and other pollinators, this approach is entirely species-specific, affecting only the targeted pest population.
The self-limiting gene is also non-toxic, so the Oxitec flies can be eaten by birds or other animals with no adverse effects. Predator feeding studies using genetically engineered insects showed there was no impact on insect predators that ingested the GE insects, even when they were fed an artificially high diet of 100% GE insects (e.g. Nordin et al. 2013). Oxitec has conducted or commissioned feeding additional feeding studies in a variety of non-target organisms such as spiders, rove beetles, fish and specific parasitoids, all using fruit flies carrying the same genes as the medfly, and in all cases no adverse effects were observed.
The self-limiting approach also means that Oxitec medflies and their offspring do not persist in the environment.
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 to support sustainable agriculture.
Who is regulating the Western Australia indoor evaluation of Oxitec medfly?
Evaluations will be conducted in DAFWA’s approved facilities. The import and use of the medfly are controlled in Australia through the Office of the Gene Technology Regulator (OGTR), the Department of Environment and the Australian Department of Agriculture and Water Resources Quarantine and Inspection Service (AQIS). As of November 2015, the Oxitec medflies were cleared from quarantine to progress into the rearing facility, with glasshouse studies slated to begin next year. For more information about DAFWA’s trial: www.agric.wa.gov.au/fruit-fly-trial-western-australia
What is the impact on organic growers?
There should be no impact on organic growers as the medflies will be evaluated in contained premises in accordance with the regulatory permits obtained. In the longer term, how GM insects will be viewed regarding organic certification will be determined by the national legislations and regulators in each country.
In the broader context, coexistence of a variety of interventions will be a consideration for both conventional and organic farmers to determine how best to support eco-agriculture and feed the growing world population in a way that is sustainable and environmentally friendly.
Who benefits from this research?
Nearly 40% of our global food supply is lost to insect pests. With a limited amount of arable land, and a growing world population, growers are under more pressure to reduce crop losses, but are faced with a reducing number of control options. In Western Australia for instance, concerns about chemical residues on crops and potential impacts on the environment have led to key insecticides being withdrawn from use.
This research is still at an early indoor evaluation stage. But if it proceeded to be used, then growers and consumers should benefit directly from more cost efficient and sustainable agriculture that protects the quality and range of fruit crops we depend on and enjoy. Protecting crop yields from devastating insect pests also improves food security to help feed the growing global population. Reducing reliance on pest control methods for which there are food safety and environmental concerns is also of global benefit.
Where can I get additional information?
You can get in touch directly firstname.lastname@example.org
DAFWA medfly website www.agric.wa.gov.au/fruit-fly-trial-western-australia
1 Leftwich, P. T., Koukidou, M., Rempoulakis, P., Gong, H., Zacharopoulou, A., Fu, G., Chapman, T., Economopoulos, A., Vontas, J., Alphey, L. (2014) Genetic elimination of field-cage populations of Mediterranean fruit flies. Proceedings of the Royal Society Biological Sciences, 281. http://rspb.royalsocietypublishing.org/content/281/1792/20141372