5 October 2019 | New Scientist | 21D
EADLY ‘super mosquitoes
that are even tougher’
accidentally created
by scientists after bungled
experiment,” shouted The Sun
in the UK. “Plan to kill off
mosquitoes backfires, spawning
mutant hybrid insects,” screamed
the New York Post in the US.
These headlines appeared last
month, in response to a critical
study of a trial carried out in Brazil
from 2013 to 2015. It released
millions of genetically modified
male Aedes aegypti mosquitoes,
which transmit serious diseases
such as dengue, yellow fever, Zika
and chikungunya. The mosquitoes
carried an added gene meant to
kill their offspring and thus wipe
out wild mosquitoes.
The shocking headlines aren’t
true, but do contain an element
of truth. We have created mutant
mosquitoes, but not because of
any genetic engineering mishap.
That story begins in West
African forests a few thousand
years ago. There, female A. aegypti
drank the blood of many species.
Over time, these mosquitoes
evolved a separate subspecies
that fed on humans. In the
15th century, slave ships carried
them to the Americas. From there,
they reached every tropical region,
allowing diseases like yellow fever
to spread to these places too. Now,
these mosquitoes are developing
resistance to the pesticides we rely
on to control them.
Such is the backdrop for the
Brazil trial, led by a company
JOScalled Oxitec. It is true that theIE^ FORDComment
Michael Le Page is an
environment reporter for
New Scientist @mjflepageViews
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The tale of the vaquita
is tense and tragic,
says Simon Ings p32“lethal” gene fails to kill up to 5 per
cent of the offspring of released
males and wild females. Oxitec
says regulators in Brazil knew this
before the trial got the go-ahead.
It is also true that the males
derive from Cuba and Mexico, so
the survival of a small percentage
of their offspring creates a mix of
three closely related strains of the
same A. aegypti subspecies. Yet
calling these hybrids is a stretch,
and there is no reason to think
they pose a greater threat, as
some have claimed.
The trial also didn’t fail: itreduced numbers of A. aegypti
in the city of Jacobina by at least
70 per cent. When the releases
stopped, the wild mosquitoes
began to rebound, as predicted.
The story of A. aegypti is no
one-off. Alter the environment
and you alter the DNA of the
creatures that live in it. The
massive changes we are making to
the planet are causing all sorts of
mutant monsters to evolve – from
antibiotic-resistant superbugs to
poison-resistant rats and bedbugs.
Genetic engineering is one of
our best hopes of controlling thesemutants we are inadvertently
creating. There are, of course, risks.
In the US, pollen from trial plots
of glyphosate-resistant GM
bentgrass for use on golf courses
spread to wild bentgrass in 2003.
Earlier this year, it emerged that
dairy cattle supposed to have only
a tiny DNA change to make them
hornless had also gained a gene
for antibiotic resistance.
But herbicide-resistant wild
grass is only a problem for those
who rely on herbicides to kill grass.
Hundreds of wild plants have
already evolved resistance without
added genes. And cows with
an antibiotic-resistance gene
wouldn’t be a major issue, even if
regulators hadn’t detected them
in time: antibiotic resistance stems
mainly from antibiotic overuse
for both people and animals.
The key question is whether the
benefits of genetic engineering
outweigh the risks. I am not
convinced that making it easier
to maintain golf courses is a good
enough reason, but hornless cattle
would make the painful methods
used to dehorn calves redundant.
As for controlling mosquitoes,
it is unclear whether Oxitec’s
approach and others like it are
practical. But surely it is worth
trying them to prevent diseases
like Zika – which can cause serious
birth defects – and judging the
results objectively rather than
spreading scare stories. ❚Mutant super-mosquitoes
Scare stories about genetic engineering are impeding genuine
advances – and masking legitimate concerns, says Michael Le Page“