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Invasive fly a threat to Mid-South fruit, vegetables

Spotted wing drosophila confirmed in Arkansas.  Invasive species can cause 100 percent losses in fruit, vegetables. Details on upcoming workshops on the new pest provided.

In 2008, yet another invasive species was found to have reached U.S. shores when California officials confirmed the tiny spotted wing drosophila was a threat to the state’s fruit crops. After spreading along both coasts and causing millions of dollars worth of damage, the pest moved inland and has now been confirmed in Arkansas.

“Basically the spotted wing drosophila (SWD) is a very small fly” says Donn Johnson, University of Arkansas professor and research/Extension entomologist. “It’s also known as a vinegar or cherry fly. It looks like and is related to the fruit fly – the type that frequent ripened bananas in your house.

“Most of the fruit flies you see in the house aren’t pests. They aren’t really causing damage to those bananas.

“However the SWD is a pest because it lays eggs in, and the larvae feed on, ripening fruit. There’s a chance the larvae can be in the fruit when harvesting.”

Among Johnson’s other comments:

Suspicions of how it reached Arkansas…

“We’re not really sure about how it’s spreading or even how it got to the United States. Originally, it came out of eastern Asia, the area around Japan. We have so much intercontinental transportation now it’s hard to stop some of these really tiny pests. People may have brought in some fruit that was infested.

“This fly is only about one-sixteenth of an inch in size. The males have a dark spot of their wings. That’s one of the distinguishing characteristics along with big, bright red eyes.

“It just showed up in the United States in 2008 so we’ve only had a short time to figure out how to monitor for it and manage it.”

Have you been expecting this pest to show up here?

“We’ve been monitoring it for the last two years in seven locations where we know there are susceptible, small fruit.

“So far, we’ve found it in three counties: Johnson, Washington and White. We use an apple cider vinegar-baited trap with a small, yellow sticky card inside. It really just looks like a beverage cup with a cap and some three-sixteenth (inch) diameter holes in the sides and lid. That allows the flies to get into the trap.

“They’re attracted to the fermenting odors that come off apple cider vinegar. We’ve also used some concord grape/vinegar and ethanol combination baits, as well.

“The traps were put near blackberry plantings and that’s where we caught the flies. None of the growers have complained of any damage to their berries, yet. So, the pest numbers are still at low numbers.

“Every state that started reporting low numbers has, in subsequent years, experienced economic damage to their small fruits. That usually takes about two years. They’re especially bad on blackberries, raspberries, blueberries and, somewhat in strawberries.”

Have the fruit industries in those states been hard hit?

“It varies. There are reports from North Carolina to Maine where growers have experienced around an average of 20 percent damage. The same is true on the West Coast from California to British Columbia.

“However, damage to crops can reach 80 to 100 percent if growers don’t act.

“Hopefully, this won’t become as big a pest here as it is on the East Coast and West Coast. But there’s certainly potential for it to become as bad.”

On management…

“Right now, the only management technique is to apply insecticides as soon as the fly is found in a trap and the fruit is ripening. Once that ripening begins, you must protect it. Usually an insecticide is applied every seven days, or reapplied after a rain.

“It’s a very new pest for this country although we’re at the point where several insecticides have been found to be useful. That’s required going through special registrations for some of the products. We’re trying to use insecticides with different modes of action so no resistance is developed in the fly populations.

“Currently, most of the damage seems to be to late-season fruits. The population of flies builds up during the growing season so most of the problem shows up after late July. The fall crops are hardest hit.

“There is no sterile insect technique to employ like typically is used against Mediterranean fruit fly.”

What about melons or tomatoes?

“We haven’t had reports on either of those. In other states they have trapped the flies in those crops but not seen larvae in the fruit itself.

“I don’t think the melons will be attacked unless they’re cracked. The same is probably true of tomatoes, even though they’re soft-skinned.”

On several other pests Johnson and colleagues are watching out for…

“We’re also monitoring for brown marmorated stink bug and kudzu bug, both invasive species.

“The brown marmorated is already causing problems on the East Coast in many fruit crops and corn. They overwinter in large numbers in homes.

“Our Extension personnel did some sampling for the kudzu bug from southern Arkansas to the east. It’s expected it will be more of a soybean pest, although it feeds on kudzu.”

Will you expand the fruit fly trapping range this year?

“We’re hoping to. We’re searching for funding to pay for three workshops to train county Extension agents and also fruit growers about SWD and how to monitor for it, what to do if they find it and to report back to me. That will allow me to put pins on the map when it’s located.”

On upcoming workshops…

“The first workshop (for growers) will be held March 13 in Hope, Ark., at the Southwest Research and Extension Center. It should begin around noon and last for two or three hours, which is the same for the other workshops.”

Note: Extension agents will be trained during morning sessions at the workshops.

“The second meeting with be April 3 in Conway at the Faulkner County Extension office. The third will be April 10 in Fayetteville at the Pauline Whittaker Animal Science Center.”

To register for the workshops, e-mail or read more about the spotted wing drosophila online here.

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