Spotted Wing Drosophila Update

Spotted wing drosophila (SWD) caused serious damage to fall raspberries and blackberries, as well as some damage to certain grape varieties across the state in 2013. The adult female of this fly is able to lay eggs under the skin of otherwise undamaged fruit just before harvest. The result is fruit that have little shelf life and contain small white larvae inside. While many soft-skinned small fruit are potentially susceptible, fruits like June strawberries have escaped due to the timing of fly activity.

UK Trap Report

There have been a large number of traps sent out to growers this year to trap for spotted wing drosophila. Patty Lucas (Princeton) and I (Lexington) have been looking through samples for SWD. The good news is that we have not found any to date, but at this time last year we had not found any either. In 2013, we recorded our first detections in mid-June.

There was a report of a fly in Central Kentucky earlier this spring, but we did not see the specimen. There has also been a report of damage to black raspberries from eastern Kentucky, but no sample was sent either. We don’t know when SWD will show up or even if it will, which is why we need to use traps in our susceptible small fruit crops. As soon as we find SWD in a sample, an alert will be sent out.

Placing Traps

My advice to growers who have crops that will be ripening is to begin trapping. Traps should be placed in crops about 2 weeks in advance of harvest so you can make a decision to spray or not spray 1 week in advance of harvest. If no flies are found, there is no reason to spray for SWD during harvest. If you decide to use insecticides during the harvest period, be careful to read and follow the label and observe Pre-harvest Intervals (PHIs) carefully.

Figure 1. A 1-quart spotted wing drosophila trap is placed inside the canopy of vines. (Photo: Ric Bessin, UK)

Figure 1. A 1-quart spotted wing drosophila trap is placed inside the canopy of vines. (Photo: Ric Bessin, UK)

Trap Bait, Processing, and Identification

The bait we are using this year is 2 tablespoons sugar and 1 tablespoon baking yeast (I use Red Star to be consistent) in 1 cup of water. Each trap gets ½  cup of bait and the bait is changed each week. You must also add one drop of dish soap to the bait to capture the flies. Pour the used bait into another container then refill the trap.

To process the samples, pour the murky trap contents through a reusable coffee filter. Adding clean water helps to flush the yeast out of the sample. Float the insects in water to check for SWD.

You are welcome to send me samples for identification, but you need to include your e-mail for a response.

More Information

There are several fact sheets on the UK Entomology Web site that discuss spotted wing drosophila:


By Ric Bessin, Extension Entomologist

Posted in Fruit
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