Australia doesn’t exactly have the best track record for pest control (unleashing myxomatosis on rabbits was a terrible idea). But we have learned a lot over the years, and it’s time to trial a new approach to deal with problem species: genetic modification.
Announced yesterday, Western Australia’s Department of Agriculture and Food will commence a trial on engineered Mediterranean fruit flies produced by British biotech company Oxitec. Due to begin next year, the study will investigate the feasibility of eventually using these agents to stamp out those that ravage the country’s crops.
The Mediterranean fruit fly, or medfly (Ceratitis capitata) is an extremely invasive species that originated in sub-Saharan Africa and subsequently spread across the globe, establishing itself as a pest in the Americas and Australasia. It’s one of the most destructive fruit pests in existence, but its taste for crops goes much further than that: more than 260 species of fruits, nuts, and vegetables have been targeted by the insect. It is thanks to this extensive range that the medfly is a year-round pest, able to flit between species that flower and fruit during different times of the year.
“One of the biggest challenges with this pest is that several key insecticides have been withdrawn in Australia over safety and environmental concerns,” Oxitec Communications Manager Dr Chris Creese told IFLScience. “Now as a result growers are having to try and control this pest year-round with fewer tools. With a finite amount of arable land, this has led to motivation to look for sustainable ways to control [medfly] and other pests.”
One such method is the sterile insect technique (SIT) which involves blasting male pest or disease-carrying insects with radiation to sterilize them. The irradiated insects are then released into target areas where they compete with native males for females. Since no offspring are produced, this can reduce the population over multiple releases. But the problem with this technique is that it weakens some insects and renders them unable to compete with the wild males.
This is where Oxitec’s solution comes in: Male insects are engineered to possess a lethal gene which, in this case, results in mated females producing no viable offspring. The idea is that if a sufficient number of females in the wild mate with these engineered males, the population will collapse. The insects are also given a fluorescent gene so that they can be tracked in the wild. A similar technique is already being employed with mosquitoes in an attempt to battle dengue fever, and trials in numerous countries are seeing successful population reductions.
Modified medflies showing presence of fluorescent marker. Oxitec.
Unlike insecticides, which can produce off-target effects, such as sickening important pollinators like bees, this method has negligible environmental impacts. The gene is non-toxic, non-allergenic and won’t be able to simply hop into other species. Creese also said that rigorous independent risk assessments are required before any of these insects are allowed to be released, which must be assured that there are no negative consequences on people or the environment.
“There have been feeding studies in which predatory species have been fed a diet consisting of 100 percent of these insects, and there have been no adverse effects,” said Creese. “That’s not representative of the situation in the wild, but it’s reassuring.”
The first phase of the multi-stage Australian trial involves so-called “glasshouse trials” in which Oxitec males are released in a tent alongside female medflies to look at their mating performance. The study will then be repeated so that competitiveness against normal and SIT males can be compared. The results of this will then dictate possible progression to larger, more informative trials.