8 | New Scientist | 7 September 2019
to Africa. We do know that the
caterpillars eat many vital food
crops, including rice, sugar cane,
sorghum and especially maize.
They can destroy a farmer’s entire
crop in a single night.
The alarm was soon sounded
in Africa. “We got involved quite
early on,” says Roger Day at the
Centre for Agriculture and
Bioscience International (CABI)
office in Nairobi, Kenya. CABI runs
clinics offering advice to farmers.Fall armyworm quickly became
one of the main concerns.
By August 2017, the pests had
spread to 28 countries in Africa.
In that time, Day’s team had
established that, if left unchecked,
infestations could destroy
between 21 and 53 per cent of the
annual production of maize in
Africa’s maize-growing countries.
That would result in an economic
loss of up to $6.2 billion.
Governments and NGOs began
drawing up action plans. There
are four key strategies, says TobyNormally found in the Americas, the fall armyworm has spread rapidly
across Africa and Asia over the past few years, devastating crops as it goes2016
2017
2018
2019SOURCE: FAOTHE race to get to grips with one of
the most destructive pests on the
planet is gathering pace. The fall
armyworm has ruined billions of
dollars of crops in Africa over the
past few years and is spreading
quickly. Last week, Japan agreed to
buy a huge consignment of maize
from the US, largely because of
fears its own crop will be eaten
by the pest. With the prospect of
this marauding insect reaching
Australia and even Europe before
long, scientists are now working
frantically to stop it.
The first thing you need to
know about the fall armyworm is
that it is actually a caterpillar, the
offspring of an innocuous-looking
brown moth. It was until recently
found just in South America and
southern areas of the US. The pest
is a big problem there, but natural
predators stop it from causing a
total disaster.
Its march further afield was
first noted in January 2016, when
unusual caterpillars were spotted
on maize plants in Nigeria. Over
the next six months, they were
found in three other west African
countries: São Tomé and Príncipe,
Benin and Togo. Three years on,
we still don’t know how they gotwhich are then eaten from the
inside when the eggs hatch. It is
wasps like this that control the
armyworm in the Americas.
Could those wasps be imported
to quash the pest in Africa?
“That requires a lot of safety
testing to make sure you’re not
introducing something that’s
going to cause more problems,”
says Day. His team is planning to
safety test one or two species in
Africa as soon as possible.
This approach has worked
before. In the 1970s, another
South American pest, the cassava
mealybug, was accidentally
introduced to Africa, causing
havoc. It was successfully
controlled by introducing
a parasitoid wasp from its
home range.
A less risky tactic would be to
use a parasitoid that is native to
Africa. Bruce’s colleagues have
been trying to identify such anRampage of the super pest
A crop-gobbling caterpillar known as the fall armyworm now threatens
much of the world. Can we stop it, asks Michael MarshallBruce at Keele University, UK.
The first is to identify crops
that are more resistant to the
armyworms, and grow those
in place of vulnerable ones.
The next two strategies are
linked. One is to grow flowering
plants like tick clovers alongside
the maize. “They release a smell
that repels the moths that lay
the eggs that develop into these
caterpillars,” says Bruce. The
farmer also grows “trap crops”
elsewhere that lure the moths
away from maize. Bruce’s team has
been trying this push-pull strategy
in western Kenya. Early tests
suggest it is effective against the
armyworms, reducing infestations
by an average of 83 per cent.
Finally, it should be possible to
unleash predators that will control
the fall armyworms. The main
candidates are parasitoid wasps.
These lay their eggs inside other
animals, including caterpillars,“The caterpillars eat rice,
sugar cane and maize, and
can destroy a farmer’s
entire crop in a night”AgricultureNews Special report