AT ANY time, maize plants are in danger
of being dismembered by the vicious
western corn rootworm larvae. When
under attack, the plants call the emergency
service for help. This service is
provided by beneficial nematode worms
that are specialized in killing the enemy.
The plant secretes a volatile compound
to call for their help.
The larvae of the western corn rootworm
(Diabrotica virgifera virgifera) are
destructive maize crop pests. They go
feed on the plant's root hairs and bore
deeper devouring the roots inside out.
The plant does not stand a chance as it
loses its nutrients supplier.
So far crop rotation, pesticides and
genetically modified maize crops have
been used to keep the enemy at bay. For
a farmer who specializes in maize, rotating
crops is not an exciting option.
Pesticides come with their side-effects.
Chlothianidine has been used for these
pests; it has also caused large-scale
honeybee deaths in Germany. As for
genetically modified crops, scientists
predict that the worm will develop resistance
to them sooner or later.
"The best way is to figure out how
they protect themselves. We found that
plants use chemicals that call bugs for
help," said Eric Schmelz from the US
Department of Agriculture.
The European maize varieties emit
the compound trans-beta-caryophyllene
(EC) to beckon for help. But the
North American varieties have lost their
ability to make the call--an unfortunate
event since the rootworm is infamous
for causing the most destruction in the
US. A team led by Max Planck Institute
for Chemical Ecology, Germany, introduced
an EC-generating gene from
oregano into the US varieties.
Bruce Hibbard from the United
States Department of Agriculture
assessed the plants' response to the
genetic addition in a maize field. The
plants effectively summoned the protective
nematode Heterorhabditis megidis.
In rows of EC-producing maize plants,
60 per cent fewerrootworm beetles
could be sighted; most of the larvae were
killed and eaten.
The experiment was successful. But
the plants turned into continuous emitters
of the compound. This might
reduce the gene's efficacy. False calls
often leave one without help at the time
of need. The gene needs modification.
"We need to make sure that the compound
is produced when the plant is
attacked by the pest," said Ted Turlings
from the University of Neuchtel,
Switzerland.
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