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Improving maize protection thanks to quicker beneficial microscopic worms

press release of June 25, 2010

In the USA, the western corn rootworm (WCR) Diabrotica virgifera virgifera is responsible for damages evaluated at one billion USD each year. In Europe, where the WCR first appeared at the beginning of the 1990's, this amount may eventually reach half a billion Euros annually. However, an injured maize plant can defend itself by emitting a specific odorous signal that attracts the pest's natural enemies: tiny worms called nematodes. In order to improve this pest control method, researchers at the University of Neuchâtel have succeeded, by a selection process, in speeding up the reaction time of these beneficial worms. This new success of the National Centre of Competence in Research Plant Survival is published today in the Journal of Experimental Biology.

Up until now, the group of Ted Turlings focused on caryophyllene, the chemical distress signal released by wounded maize roots to attract the insect-killing nematode Heterorhabditis megidis. The nematodes infect the root-eating larva and indirectly ensure a protection for the plant. Ivan Hiltpold, one of the main authors of this study, is interested in improving the other partner in the defence process: the nematodes. In the newly published experiments he figured a way to increase the efficiency by selecting individuals that reacted to the root signal the quickest. 

To achieve this, the biologist measured in the lab the time it took for nematodes in a labyrinth filled with sand to reach a synthetic source of caryophyllene. The fastest 500 individuals were used to produce the next generations, thus the 500 that reached the signal first were selected to reproduce. By repeating this process six times, Ivan Hiltpold was able to form a "dream team" whose travel time for 500 worms went from twelve to five hours!  The selection process was performed on the nematode Heterorhabditis bateriophora, a species that is very effective against corn rootworm, but until now did not react very strongly to caryophyllene.

The selected nematodes, however, still needed to prove their worth in the field. In Hungary, a region in Europe that is particularly affected by Diabrotica, researchers of CABI-Europe-Switzerland run a field station in Hungary and provided fields sowed with two maize varieties: one that produces the caryophyllene and the other that does not. In these maize fields, Marianne Baroni, a master's student supervised by Ted Turlings and Ivan Hiltpold, was able to show that after a treatment with nematodes the maize varieties that emit caryophyllene received less root damage than those that did not. Indeed, the selected nematodes had killed more pest larvae than their counterparts that did not undergo the selection process.

Because of this study, Ted Turlings' team was able to show that manipulating natural enemies is a realistic approach with great potential for improving biological control methods. The scientists had already demonstrated that plant manipulation with the aim of improving the distress signal is feasible. The weak link that remains in this system is the costly and inefficient application of the nematodes. Ted Turlings obtained a federal grant that promotes the collaboration between industry and the academic world. This grant will allow Ivan Hiltpold the development of new technologies that optimize the application of these promising biological control agents.

contacts

University of Neuchâtel
FARCE Lab
(Fundamental and Applied Research in Chemical Ecology)

Prof. Ted Turlings
ted.turlings@unine.ch
Tél. +41 32 718 31 58

Dr. Ivan Hiltpold
ivan.hiltpold@unine.ch
Tél. +41 32 718 31 43

Scanning electron microscope image of nematodes Heterorhabditis bacteriophora.
© Ivan Hiltpold & Michèle Vlimant, Université de Neuchâtel