Dial 100

AT ANY time, maize plants are in dangerof being dismembered by the viciouswestern corn rootworm larvae. Whenunder attack, the plants call the emergencyservice for help. This service isprovided by beneficial nematode wormsthat are specialized in killing the enemy.The plant secretes a volatile compoundto call for their help.

The larvae of the western corn rootworm(Diabrotica virgifera virgifera) aredestructive maize crop pests. They gofeed on the plant's root hairs and boredeeper devouring the roots inside out.The plant does not stand a chance as itloses its nutrients supplier.So far crop rotation, pesticides andgenetically modified maize crops havebeen used to keep the enemy at bay. Fora farmer who specializes in maize, rotatingcrops is not an exciting option.Pesticides come with their side-effects.Chlothianidine has been used for thesepests; it has also caused large-scalehoneybee deaths in Germany. As forgenetically modified crops, scientistspredict that the worm will develop resistanceto them sooner or later.

"The best way is to figure out howthey protect themselves. We found thatplants use chemicals that call bugs forhelp," said Eric Schmelz from the USDepartment of Agriculture.

The European maize varieties emitthe compound trans-beta-caryophyllene(EC) to beckon for help. But theNorth American varieties have lost theirability to make the call--an unfortunateevent since the rootworm is infamousfor causing the most destruction in theUS. A team led by Max Planck Institutefor Chemical Ecology, Germany, introducedan EC-generating gene fromoregano into the US varieties.

Bruce Hibbard from the UnitedStates Department of Agricultureassessed the plants' response to thegenetic addition in a maize field. Theplants effectively summoned the protectivenematode Heterorhabditis megidis.In rows of EC-producing maize plants,60 per cent fewerrootworm beetlescould be sighted; most of the larvae werekilled and eaten.

The experiment was successful. Butthe plants turned into continuous emittersof the compound. This mightreduce the gene's efficacy. False callsoften leave one without help at the timeof need. The gene needs modification."We need to make sure that the compoundis produced when the plant isattacked by the pest," said Ted Turlingsfrom the University of Neuchtel,Switzerland.