CO-Horts Blog

Monday, August 11, 2014

August 11, 2014
Posted by: Mary Small, Jefferson County Extension

Got Mushy Raspberries?

They’re here and they’re gross. I’m talking about the spotted wing drosophila (SWD) in our Research and Demonstration garden’s raspberry planting.
SWD ovipositor, serrated and sclerotized

Of course, these little gems have to be different than other fruit flies. The females have a sclerotized (hardened) serrated ovipositor, (egg-laying structure) just right for laying eggs in intact, still-ripening fruit. They couldn’t be like their relatives who are more interested in fallen or overripe fruit, no!

What’s so disgusting about the whole thing is that the larvae rapidly turn raspberries into a liquid mess. One morning, a staff member collected a small bag for a snack later in the day. When she went to eat them, the now liquefied fruit was infested with tiny white maggots.

Liquified raspberries with maggot (just above center)

While they will damage many types of small fruit, peaches and cherries, they prefer the volatiles of raspberries. To add insult to injury the insects feed on other soft- fleshed fruit found in our landscape – elderberries, chokecherries, mahonia and honeysuckle. So there’s plenty of food to keep them hanging around, even if it’s not their favorite!

We first found SWD late last summer and began a sanitation program: keeping fruit regularly picked and collecting fallen fruit from the ground. We started a trapping program in July using a yeast-sugar water bait placed in red-lidded empty peanut butter jars. (Thanks to my dedicated family for eating all the peanut butter!)  While we’ve collected mostly male and female SWDs, it is interesting to see who else likes the bait. So far, we’ve also collected sap bugs, earwigs and other fruit flies. 
Trap for SWD 

This year we’re using sanitation and trapping to monitor the population and sort-of manage it. Being a garden on public property that can be accessed virtually any time of day, we’re a bit reluctant to introduce pesticides.

One of the benefits of the infestation is that we have a living laboratory for training our volunteers.  The clinicians will also be able to identify the adults after an upcoming workshop, so they can better assist customers.

And frankly, when I check the raspberry fruit I am amazed at how many thrips are wandering around in them. I wonder how many I've consumed over the years.  Maybe I should just view SWD in the same way – extra protein, anyone?


  1. Please give the recipe for the yeast-sugar water trap and how did you prepare the lid? Thanks.

  2. Great article Mary! Eat them immediately... or refrigerate... or freeze and eat later. Yes, it's probably not a good idea to think about how many thrips and other insects one eats with produce (without harm, by the way).

  3. Here is the recipe from Cornell Extension:

    Fermenting Dough Bait recipe
    – enough for one specimen container
    1/2 tsp Sugar (2 g)
    1/8 tsp dry active bread yeast (0.325 g)
    2 TBsp whole wheat flour (17.25 g)
    1/5 tsp apple cider vinegar* (1 mL)
    1 fl oz water* (25 mL)

    Use a lid that the drosophila cannot get a No-See-Um fabric or other very fine mesh. If there's a lid that comes with your cup, that will work too (think of a fast food cup). Link to Cornell Extension's publication: