Last year was difficult enough for vintners in many of Europe's leading wine regions, thanks to a gray, wet summer that slowed grape ripening and encouraged mildew. But they also had to grapple with a new pest during the 2014 harvest: a foreign fruit fly. Drosophila suzukii, commonly known as the spotted wing drosophila, was first spotted in Europe in 2008. And last year's weather encouraged a population swell that left grapegrowers wrestling with an unfamiliar pest. They're worried this year could bring more flies—and trouble.
The fly is native to southeast Asia but was discovered in western countries in 2008 with three simultaneous outbreaks in California, Spain and Italy. The flies were first found near ports, suggesting they had traveled in shipped fruits from Asia. In 2009, the fly was found all over Europe and North America.
Drosophila suzukii is a close relative of Drosophila melanogaster, the common fruit fly or vinegar fly native to Europe and North America. Fruit flies are a scourge in vineyards, but they only feed on damaged or rotten fruit. Spotted wing drosophila, in contrast, target healthy, ripening fruit—female flies puncture the skin of fruit so that they can lay their eggs just underneath the surface. The larvae then hatch and eat the fruit from within.
What made 2014 such a banner year for the new pest was the weather. “Mild winters and summers as well as wet weather are conducive to rapid population increase," said Vaughn Walton, an associate professor in entomology at Oregon State University. "Spotted wing drosophila population [growth] reaches a peak during wine harvest.” In 2014, temperatures never got low or high enough in Europe to stave the frequent reproduction cycle of the fly, and humid weather around harvest exacerbated the infestation.
The weather was especially favorable for the pest in Alsace and Germany. “All the conditions were there, so we expected problems [from native fruit flies],” said Olivier Humbrecht, of Domaine Zind-Humbrecht. “What we didn't expect was the importance of the Asian drosophila. I estimate that we lost about 15 percent of the crop" after damaged fruit was discarded.
Growers across Europe reported fruit flies as a problem during the harvest, but other regions were slower to single out the Asian fly as the culprit. “On the Côte-Rôtie sector, out of the 14 samples of grapes taken by the agricultural chamber there was no presence of Drosophila suzukii, only the Drosophila melanogaster,” said Philippe Guigal of E. Guigal.
The Asian fly was widely reported in Italy. Renzo Cotarella, CEO and chief winemaker at Antinori in Tuscany, said their workers avoided the problem with “a lot of leaf removal, enhancing the aeration of the fruit.” But he noted that, “some of the producers, especially the ones under organic management, had some problems in the last period of the harvest.”
Luca Currado of Vietti in Barolo, who practices organic farming, said he experienced problems with almost the entire harvest. “First damage we saw was in Moscato in late August, then we saw them in all the other varieties, one by one, as they arrived to maturity,” he said.
Whether organic or "conventional" growing techniques affect the pest is unclear. Back in Tuscany, Giovanni Manetti of Fontodi believed that a combination of organic growing and the high altitude of his Chianti Classico vineyards kept the new fly away from his grapes. Humbrecht, who also grows organically, believes that it has no effect—the fly population swells close to harvest when insecticides are outlawed.
Although Currado had difficulties, he was quick to point out, “[the consumer] should see a loss in production, not in quality. Much slower harvest time, much higher cost.” Veronique Muré of Alsace's Domaine Muré hired twice the usual number of pickers than normal. All producers, whether they singled out the spotted wing drosophila as a problem or not, said that the 2014 harvest was one of the hardest they had experienced.
The pest may be a growing problem going forward. There are not many insect competitors for the fresh fruit, they are resilient in a wide range of conditions, they can travel long distances in a wide range of hosts and they reproduce extremely rapidly compared to their Western cousin.
Oregon State University's Walton said that biological control agents are showing a lot of promise. He hopes that by releasing another insect—a successful biological competitor—the fly population can be controlled before and during harvest. Humbrecht thinks that a natural predator could take care of the problem. But, he conceded, “It could take a really long time.”