Germany
July 28, 2008
Source: PULS-CE, Newsletter of
the Max Planck Institute for
Chemical Ecology, Issue 11
http://www.ice.mpg.de/newsletter/Newsletter11_en.pdf
In 2005, the results of a fruitful
cooperation between the University of Neuchatel, Switzerland,
and our institute resulted in a
Nature paper.
The scientists reported that maize roots damaged by corn
rootworm (Diabrotica virgifera virgifera) recruit
entomopathogenic nematodes as an indirect defense by emission of
(E)-beta-caryophyllene1. So the ecological principle of indirect
defense - “The enemy of my enemy is my friend” - works
underground as well! This harmful insect species was
unfortunately already well known as a pest of maize in the USA,
where farmers combat it using crop rotation, insecticides, and
increasingly by growing preferred transgenic Bt-maize varieties.
Because of its devastations in the USA, Bernd Dörries from the
German Süddeutsche Zeitung (SZ) called the corn rootworm the
“one-billion-dollar bug”: the pest can cause harvest losses of
up to 80% (SZ, 15/16.9.2007).
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Corn rootworm
Diabrotica virgifera virgifera
Picture: Baufeld, Julius Kühn Institute |
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Corn rootworm was accidentally
introduced into Serbia in 1992 and has rapidly spread through
southern Europe. Last year, adults made their debut in pheromone
traps in southern Germany, and only two days later, on July 25,
2007, the BBA in Braunschweig (now the Federal Research Centre
for Cultivated Plants) reported that all necessary and mandatory
measures against the pest had been taken. Facing this serious
new threat
to maize production, the agricultural minister of
Baden-Württemberg Peter Hauk strongly recommended that farmers
should not grow genetically modified maize to fight the insect
pest (Stuttgarter Nachrichten, 16.8.2007) - such plants are
still not approved in the EU anyway. A few days later, the first
action taken was to treat an area of about 3000 hectare with
agrochemicals, according to the newspaper. This was despite the
warning made by the environmental protection organization BUND
(Bund Umwelt und Naturschutz) against the use of any
insecticides to fight the corn rootworm, because not enough
tests on the effects on humans and the environment had been
carried out.
For further control, the Federal Office of Consumer Protection
and Food Safety (BVL) ordered maize seeds to be treated with the
insecticide Clothianidin (SZ, 18.6.2008). This broad-spectrum
active ingredient is known to be harmful to bees and is
therefore approved only for direct application to seeds. After
planting, Clothianidin protects the plant against corn rootworm
from underground, away from the bees. But then something
unexpected happened: During planting, dust from certain types of
sowing machines was emitted from abraded maize seeds. The BBA
quickly found out that the Clothianidin-contaminated dust was
responsible for the loss of 330,000,000 bees (about 11,500
colonies) in Baden-Württemberg in spring 2008 (SZ, 24.7.2008).
Again, Minister Hauk made a public statement and immediately
offered financial compensation for the beekeepers.
Conclusion: What lessons can we learn from the corn rootworm? As
well as providing a new example of a growing
paradigm in chemical ecology, it reminds us that plant
protection is an increasing challenge for mankind. Just as
scientific collaboration sheds light on hidden, underground
interactions, global co-operation will be required to protect
nutrition, harvests, and food supplies from insects that are
rapidly becoming global pests. For this purpose all available
methods and technologies should be considered, including
rootworm-resistant transgenic
maize as successfully developed and used in the USA. Premature
ministerial pronouncements can illustrate the
dangers of failing to evaluate whether the use of genetically
modified maize on certain acreages may or may not
be safer than agrochemistry or special cultivation practices.
And finally, the “enemies of the enemies” of the
“Pesticide Treadmill” could learn from the “German bee accident”
that they do have some goals in common:
a reduction of dependency on chemical insecticides, whether by
biological control, transgenic crops, or both.
Update: The corn rootworm keeps coming - in late July this year,
34 corn rootworm imagos were trapped in Baden-Württemberg and
two in Bavaria.
1 Rasmann S; Köllner TG;
Degenhardt J; Hiltpold I; Toepfer S; Kuhlmann U; Gershenzon J;
Turlings TCJ (2005): Recruitment of entomopathogenic nematodes
by insectdamaged maize roots. NATURE 434, 732-737. |
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