Fall armyworms with offspring-killing gene tested on farms in Brazil

Male fall armyworms carrying a gene that kills female offspring were released on farms in Brazil as a possible way to control wild populations of a major pest

By Michael Le Page

Fall armyworms genetically modified to wipe out wild populations of the pests have been released in corn fields in São Paulo State in Brazil in the first farm trial of the new technology. The test was a success and is now being expanded, says Oxitec, the UK-based company that created the modified armyworms.

Fall armyworms (Spodoptera frugiperda) are in fact moth caterpillars. They get their name from the fact that they multiply very fast and feed on many plants. Swarms of armyworms can devastate everything from lawns to crops in just days.

They are native to the Americas, but in recent years have spread across Africa, Asia and Australia, reducing harvests of some crops by up to half. Conventional control methods aren’t working well because some strains have evolved resistance to many pesticides.

“There is a lot of interest in new solutions to this pest,” says Neil Morrison at Oxitec. “Growers are struggling to control it through insecticidal means.”

For its method of control, Oxitec took a strain of fall armyworm that is still susceptible to pesticides and modified males so that their female offspring can survive only in the presence of a specific chemical. In other words, the males carry a gene that kills all their female offspring in the wild.

When the modified fall armyworms are released, they mate with wild females. Only male offspring survive, and they can mate and spread the female-killing gene to another generation. Unlike with pesticides, no other species are harmed.

If no more “Friendly™ fall armyworms”, as Oxitec calls them, are released, the female-killing genes rapidly disappear from the wild population. If large enough numbers of modified males are released, wild armyworms can be wiped out locally.

That is the theory, at least. Future trials will evaluate effectiveness, says Morrison. The initial farm trial was only intended to test whether the released males behave as expected.

“For instance, after we stop releasing, does the self-limiting gene disappear from the environment? Yes, it does,” he says.

The approach has already been approved in Brazil. “We can deploy those Friendly males anywhere in Brazil without restriction,” says Morrison.

Oxitec is already selling “Friendly™ Aedes aegypti” mosquitoes in Brazil to prevent the spread of diseases such as Zika and dengue. On 8 March, it got the go-ahead for their use in pilot projects in California and Florida.