Invasive insect threatens berry crop

Monday June 3, 2013

BRATTLEBORO -- Vermont has one more invasive insect to be concerned about.

The spotted wing drosophila, an invasive insect that lays its eggs in soft fruit and can damage raspberries and blueberries, was found in New England in small numbers in 2011 and then again, in much larger numbers, last year.

Scientists are expecting the worst this year as the tiny fly continues spreading across the country.

"We had a handful of reports last year and now we're pretty confident it is going to be everywhere this year," said Vern Grubinger, University of Vermont Extension vegetable and berry specialist.

The spotted wing drosophila was first discovered in California in 2008 and by the following year it had spread all the way to Florida.

It has been traveling north ever since and was discovered across the Northeast in 2012.

The spotted wing drosophila is related to the common fruit fly, which lays its eggs in rotting fruit, but the female spotted wing drosophila has a saw-like egg laying appendage that allows it to drill into ripe soft fruit and lay its eggs in the small holes.

They soon hatch and the larvae feed in the fruit's flesh for about 10-14 days before emerging as adults.

Females can lay 300 eggs in their lifetime.

The insects are especially challenging to detect because the tiny holes are hard to see and the fruit can be harvested and then soon rot as the larvae emerge and begin feeding on the flesh of the fruit.

Grubinger said he received frantic calls from growers during the harvest last year when the fruit began to rot after the berries were picked.

And the spotted wing drosophila also has the ability to survive in a variety of plants ranging from blueberries, to wild raspberries to pokewood and Korean dogwood, so Grubinger said the Northeast is particularly susceptible due to its highly diversified landscape.

Scientists believe the insect came from northern Japan and can survive cold winters.

Grubinger was at a one-day conference in Connecticut in April with scientists from across New England and he said growers and specialists across the region are experimenting with traps and methods for repelling the flies.

"This is a new pest and we going to monitor it closely," said Grubinger. "We are still experimenting. This is not the end of our fruit growing. It just means we're going to have to learn about their behavior and find out what strategies work to help keep it down to a dull roar."

Grubinger says the best, and most environmentally sound, way to control the infestation is by draping a very fine mesh net over the blueberry or raspberry bushes, though netting can get expensive.

He also recommends picking the fruit just as it ripens and quickly freezing or refrigerating the berries.

If the fruit is left ripe on the bush, or picked and left at room temperature, the larvae have more opportunities to hatch.

He said the larvae and flies pose no risk to human health, and even if they are in the berries the tiny eggs are almost impossible to detect.

Commercial growers have been hearing about the aggressive pest for the past few years but home gardeners might be surprised by how much damage they can do.

"People don't have time to pay attention, but if you didn't know about it before you got it, you're certainly going to pay attention next year," he said.

Ann Hazelrigg, who runs the UVM Plant Diagnostic Clinic, helped organize a trapping program in Vermont last year and is getting the traps out again this season.

Hazelrigg said scientists think the fly blew north on winds during Tropical Storm Irene and have now found a whole host of plants to feed on in New England.

At this point in the season Hazelrigg says scientists are trying to learn what they can and let every grower know what they can do protect their fruit.

"This a devastating pest and we're trying to prevent the population from building up," said Hazelrigg. "We're trying to get the word out because I really don't see this problem going away."

For updated information go to Grubinger's web site at

Howard Weiss-Tisman can be reached at 802-254-2311, ext. 279, or Follow Howard on Twitter @HowardReformer.


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