Science and Technology

A Threat to European Corn

Unwelcome American: The western corn rootworm beetle appeared in Serbia in 1992 and has spread to Western Europe (Photo: USDA).

“Unfortunately, it’s already progressed so far that we can’t wipe it out,” says Sylvie Derridj, a specialist on the Diabrotica virgifera virgifera. She’s worried that this beetle [known as the western corn rootworm beetle] will now become entrenched in Europe after having ravaged America’s corn crops.

Derridj is a scientist in the pesticide and chemical agent research lab of the National Agronomic Research Institute in Versailles. She is one of the few people in France working to stem the advance of this Chrysomelidae-family beetle, which, after having attacked plants of the Cucurbitaceae family (gourds and pumpkins), turned into a devourer of corn in the Corn Belt, in North America’s Midwest. The battle against this nuisance and the resulting loss of production—up to 80 percent in some fields—are costing between US$650 million and $1 billion a year.

The Diabrotica is a fiercely determined traveler. In Europe, it was detected for the first time around the Belgrade International Airport in 1992, near the hangar where American
fighter planes were cleaned and maintained. It seems the insect had arrived there a couple of years earlier. Since then, its march has been unstoppable: Hungary and Croatia in 1995; Romania in 1996; Bosnia in 1997; Bulgaria, Montenegro, and Italy in 1998; Slovakia and Switzerland in 2000; Ukraine in 2001; Austria in August of this year. It was also in August that the first chrysomelids were found in France, around the Paris-area airports at Roissy, Orly, and Le Bourget, where the authorities had installed pheromone traps.

Pheromones are natural chemicals that act as sexual markers—to attract the male Diabrotica. Since August, eradication measures have been put in place. But the mobilization comes very late. The authorities fear that the infestation is already quite advanced, judging from the fact that they’ve trapped very large numbers of adult insects—as many as 135 adults in a single trap at Roissy, despite the fact that the traps’ attraction zone extends just 10 meters. Emergency chemical treatments have been done, and they may take care of the adults, but they won’t touch the eggs and larvae in the ground, which will hatch in spring.

Derridj believes that the 300 or so traps that have been set out this year (compared with just 15 before) won’t be enough to gauge accurately the scale of the infestation. “We have got to put them out in all the corn-growing areas and among other crops,” she says.

It appears that Diabrotica hops on modern transportation—the insects have also been discovered around the airports in Italy and Switzerland—and is thus able to make great bounds across the landscape, to the astonishment of some of those who study it. In any case, even without taking the plane, invading Diabrotica will advance naturally by 20 to 40 kilometers [12.5 24.8 miles] per year. The beetle may already be in Beauce, France’s great grain basket southwest of Paris, without anyone’s being the wiser. Until traps are placed in the area, it will be difficult to know.

To judge by the American experience, Europe’s struggle against Diabrotica is likely to be long and hard. Diabrotica’s salad days began about 50 years ago, when single-crop corn cultivation developed into large-scale business. American farmers initially battled the bug with insecticides, but Diabrotica became resistant to these, necessitating ever more powerful products that would remain in the ground where they are supposed to kill the larvae.

A “green” counterattack was also developed, which consists of rotating the corn crop with soybeans. Because the larvae feed on the roots of the corn plant, when the field is planted with another crop, they find nothing to eat and die of hunger shortly after hatching. But Diabrotica’s behavior makes things difficult even when crops are rotated. Some females lay their eggs in the soy field in the fall, allowing their offspring to be born in a cornfield the following spring. Other females lay eggs whose diapause, or hibernation period, may last two or three winters, again allowing the larvae to hatch in a field newly seeded with corn. So American farmers have had to return to chemicals to battle the beetles.

A European program to study milder methods of fighting Diabrotica hasn’t met encouraging results, either. Test crop rotations conducted in Hungary have shown that the insect can lay its eggs in places other than cornfields. Genetic analysis should be able to determine by the end of October whether this species of Diabrotica is the same one that appeared in Illinois in 1987 and is able to beat farmers at the rotation game. French scientists still don’t know whether the insects trapped in this country are of that same variety, Derridj notes.

Research on natural predators in Europe has been fruitless. A team of Swiss scientists went to Mexico and found a parasite that sucks the larvae. But before the Europeans introduce this biological weapon, they’ll have to be certain it won’t attack other species of beetles, a process that could take years. Tests on “disorienting” the females have taken place in Hungary, where both pheromones and cheromones—natural botanical agents—have been sprayed on fields to discourage the insects from mating.

It is too early, however, to say whether this will work. Derridj doesn’t believe that genetic engineering is a panacea against these determined pests. She thinks the battle will have to employ a number of different weapons. But already, Monsanto and Pioneer, two agrochemical corporations, are developing corn whose genes have been altered by the introduction of a natural insecticide of Bacillus thuringiensis, which renders the grain resistant to Diabrotica. In the United States, Monsanto is seeking government permission to sell seed from its corn variety MON 863. In France, Monsanto cited Diabrotica when it asked the biomolecular engineering committee for permission to test its product in 1999. Pioneer carried out tests of genetically altered corn in several villages in the Charente and Haute-Garonne departments [in southwestern France] in 2000 and 2001.

According to the Committee for Research and Independent Information on Genetic Engineering (CRII-GEN), an activist movement against genetically modified (GM) organisms led by Corinne Lepage (one of the dozen-plus candidates in France’s recent presidential elections), the ability of the multinational agrochemical companies to react so rapidly to the Diabrotica invasion is suspicious.

The chairman of CRII-GEN’s scientific committee, Gilles-Eric Séralini, speculated in his recent book, GM Foods: The Real Debate, on the coincidence of Diabrotica’s introduction to Europe by American armed forces and the American companies’ putting forward genetic engineering as a way to fight the pest. Séralini denounces “a policy that would introduce GM through a sort of ecological blackmail whose origins ought to be carefully investigated.” He mentions evidence supporting his speculation, but doesn’t produce it.

The companies deny this theory. The Diabrotica beetle has been a major pest in the United States for decades, and the adaptation of genetically altered varieties capable of resisting it can be done rapidly, Monsanto officials say. Nonetheless, Monsanto isn’t researching this kind of adaptation for Europe at present, because of the European moratorium on genetically modified organisms.

For its part, CRII-GEN asserts that Diabrotica mustn’t become a Trojan horse that would bring about a lifting of the moratorium.