Genetically engineered flies could save fruit crops

13 August 2014 by Harriet Jarlett

Fruit crops ravaged by the Mediterranean fruit fly could be saved by genetic engineering, say scientists who have altered the genes of some male flies so they can only produce sons.

Two fruit flies matingMediterranean fruit flies are global pests that have serious consequences for agriculture. Their numbers are currently controlled by a combination of insecticides, baited traps, biological control and the Sterile Insect Technique (SIT) - where male flies are treated with radiation to make them sterile before they're released into the wild.

SIT is the most commonly-used method to control the flies and considered the most environmentally friendly because the technique simply interrupts the insects breeding cycle. But males which have been treated to make them sterile don't tend to mate as well in the wild because the irradiation method used for sterilisation weakens them.

This new NERC-supported study, published in Proceedings of the Royal Society B, found that genetically engineered flies from Oxitec Ltd are healthier than the flies used for SIT programs, which also means that females are no less likely to mate with them compared to wild males.

If the males are healthier and more attractive you don't need to release as many - it brings down costs.

- Dr Leftwich, University of East Anglia

"SIT is a great idea as it's completely species specific, and it massively reduces the amount of insecticide used, but because females prefer healthier males you need to try and introduce more sterile males than will be in the wild," explains Dr Philip Leftwich of the University of East Anglia, lead researcher on the project. "The idea with genetically engineering the flies is that you get much healthier flies which haven't been damaged by irradiation. If the males are healthier and more attractive you don't need to release as many - it brings down costs."

"The genetically engineered males aren't sterile, just incapable of producing daughters, so when we release them into the population and they find females, unlike SIT males, they're actually fertile, so they use up the females' eggs, whereas in SIT females can and do simply re-mate with a wild male. The sons carry the gene too so they help with the process, as they'll only have half as many daughters. Eventually it causes a sex bias in the population and it will collapse," he explains.

The team simulated a wild environment using large greenhouses at the University of Crete filled with lemon trees. They compared genetically engineered flies against the wild type fly population they were created from and the flies which have been bred to take part in SIT.

To test their health they observed them to see how well they survived in a variety of conditions, such as with little or no food and water. They also tested the flies to see if there was any bias during mating to choose genetically engineered or wild males.

"One problem with traditional SIT is that females in the wild would rather mate with a wild male than an SIT male, probably because they're less healthy. But in our tests we found females would mate with either a wild or a genetically engineered type of male, they didn't seem to care," Leftwich says.

Leftwich believes that the genetically engineered flies could provide a better alternative to SIT for controlling this pest.

"SIT is quite limited as you can only have facilities in places that are regulated to handle radiation materials," he says. "Using genetic engineering instead would make it easier for more facilities to use the technology."

"I think the most important point is just how much better the while process should work. The flies are healthier, still fertile, so it overcomes the problem of females remating and ultimately should prove more cost effective. Which in turn leads to a reduced need for insecticides and means a more environmentally friendly approach," Leftwich concludes.

The team now hope to be able to get approval for open-field studies.

PT Leftwich et al, 'Genetic elimination of field-cage populations of Mediterranean fruit flies'. Proceedings of the Royal Society B 20141372.

This work was funded in part through a NERC open CASE PhD studentship to Tracey Chapman and to Oxitec Ltd. Philip Leftwich received financial support from Oxitec through the NERC open CASE studentship scheme.