Mutant animal armies

(Image: David Scharf/Science Faction/Getty)

Here's a fascinating article from New Scientist:

In the urban jungle of Juazeiro in Brazil, an army is being unleashed. It is an army like no other: the soldiers' mission is to copulate rather than fight. But they are harbingers of death, not love. Their children appear healthy at first but die just before they reach adulthood, struck down by the killer genes their fathers passed on to them.

These soldiers are the first of a new kind of creature - "autocidal" maniacs genetically modified to wipe out their own kind without harming other creatures. The first animals being targeted with these "living pesticides" are disease-carrying mosquitoes and crop-munching caterpillars, but the approach should work with just about any animal - from invasive fish and frogs to rats and rabbits. If it is successful, it could transform the way we think about genetically engineered animals. ...

In theory, unlike zapping animals with radiation or chemosterilisation, the genetic approach should work well with just about any species. Besides the pink bollworm, Oxitec is targeting the mosquito Aedes aegypti, the single most important carrier of dengue, a viral disease that affects 50 to 100 million people in tropical regions every year,...

[Luke] Alphey and his colleagues have created a strain of A. aegypti with two copies of a gene that disrupts the development of offspring. The gene is switched off in the presence of the antibiotic tetracycline, allowing large numbers of perfectly fit mosquitoes to be bred for release. "With our system, the mosquitoes are fundamentally sterile and we're keeping them alive by giving them an artificial antidote," says Alphey. The insects also have the DsRed marker gene, to enable them to be easily monitored.

When these mosquitoes mate with wild females, the eggs hatch and the larvae develop normally until they reach the pupae stage, when the killer genes kick in. Delaying death like this is actually a cunning trick: the doomed larvae compete with wild larvae for resources, further reducing their numbers. ...

Transporting adults is not feasible. "Adult mosquitoes are all spindly and if you pack them into any kind of space, you end up with legs tangled up with wings and a lot of physical damage," says Alphey.

Instead, his team has created a strain in which the females cannot fly. The work was based on the discovery that female mosquitoes have a unique flight muscle protein that males lack, perhaps because females have to fly after a blood meal and so must fly with a much heavier load. Flightless females cannot find people to feed on and cannot mate either, so there is no need to separate the sexes. Envelopes containing millions of eggs could simply be mailed to wherever they are needed. "Just add water and you get instant mosquitoes," says Alphey.

The males that hatch from the eggs will appear normal and can pass the flightless gene to their daughters. Their sons will also inherit a single copy, so they too will produce some flightless daughters. "The construct will persist in the population for several generations but not for long due to its high fitness cost," says Alphey.

Neat, isn't it? Yet some Luddites are so opposed to genetic engineering that they have a knee-jerk response even to this. Nothing, I suppose, is 100% safe, but this seems to be about as close as you can get.

And doing nothing is certainly not safe.

[I]f autocidal technology lives up to its promise, it could be about as environmentally friendly as pest control can get. It could largely or entirely replace pesticides, and it affects only the target species. Last but not least, it is hard to see what could go wrong.

Many engineered plants, for instance, are being given advantageous traits such as disease resistance, so these genes could well spread among wild relatives. Autocidal traits, by contrast, are a great disadvantage and should disappear from the wild within a few generations after releases stop. "We are putting genes with huge, huge fitness penalties like death into something that's undesirable in the first place," says Alphey.

In theory, wild insects might be able to evolve resistance, for instance, by somehow learning to recognise and avoid insects with lethal genes. But this is much less likely to develop than pesticide resistance, and could be overcome by altering the release strain.

Needless to say, those opposed to genetic engineering are not convinced. "Genetic modification leads to both intended and unintended effects," says Ricarda Steinbrecher of EcoNexus, which describes itself as "a not-for-profit, public interest research organization". "There are potential knock-on effects on many other organisms," she claims.

Most biologists, though, agree the risks are minimal. "It is true that some of the regulations are being put together as the programmes are moving along, but the risks are really very, very small," says Mark Benedict, an entomologist at the University of Perugia in Italy.