Worm Resurgence Troubles Apple Farmers

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Organic apple farmers keep their fruit free of worms by spraying their trees with a naturally occuring virus. But insects in some orchards in Germany have developed resistance to this biological insecticide and farmers are concerned.


If you bite into an organic apple…

(Soundbite of chewing)

SIMON: …like this one and it doesn't have any worms, chances are some farmers sprayed it with a virus. But don't worry the virus won't hurt you, that only infects an insect pest, the codling moth. Now in a few orchards in Germany though, these insects are surviving doses of the virus and apple growers are scared.

NPR's Dan Charles has more.

DAN CHARLES: Wherever a codling moth finds an apple, it lays its eggs, worms hatch and dig right in, distressing farmers and disgusting consumers.

Dr. LARRY HALL (Entomologist, Pen State University): Obviously, no one likes to bite into an apple and see a worm staring him in the face.

CHARLES: Larry Hall is an entomologist with Penn State University. He studies insects that afflict fruit trees including the codling moth.

Dr. HALL: It's become a pretty severe pest and has developed resistance to a lot of the insecticides that growers commonly or use at least they used to use.

CHARLES: But the codling moth has a natural enemy, the codling moth granular virus. Scientists found it first in sick moths collected in Mexico. Companies now grow lots of the virus by infecting swarms of the insects. They mash up the dead moths, package the resulting liquid and sell it to farmers to spray on apple trees. This biological insecticide caught on first among Germany's many organic farmers almost 20 years ago.

Johannes Pfeil(ph) works for the agricultural service center in the German state of Rheinland Platenhof(ph).

Mr. JOHANNES PFEIL (Agricultural Service Center, Rheinland, Platenhof): It's much more important for the organic because they don't have any chemicals. But actually its the key product in the organic production of apple to control the codling moth.

CHARLES: In the last two or three years, apple growers in the U.S., mostly organic growers, have started using it too. But in Germany, in a few orchards wormy apples recently reappeared.

Farmers called in a team of scientists to figure out why. And in this week's issue of Science Magazine, the researchers announced their answer: codling moths have evolved resistance to the virus. In 13 orchards in Southern Germany, moths can survive on average a dose of the virus a thousand times higher than what would kill a typical moth. This was little bit shocking.

David Heckel from the Max Planck Institute for chemical ecology in Jena, Germany, says many people didn't believe insects could become resistant to a virus.

Dr. DAVID HECKEL (Director, Max Planck Institute of Chemical Ecology): Even though viruses have been used in agriculture and forestry for a long time. There has never really been reported any problems of the insects developing resistance to it.

CHARLES: This resistance emerged and spread very fast. For apple growers who rely on the virus, it's an alarming development. But there is some good news. The moths have evolved resistance only to one strain of the codling moth granular virus, the one that's sold commercially. But there are other strains collected from sick moths in other parts of the world. Those strains of the virus still work. So there is still hope. You can avoid that unpleasant encounter with an apple worm.

Dan Charles, NPR News, Washington.

(Soundbite of chewing)

SIMON: This is NPR News.

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