Spotted wing drosophila monitoring recommendations for 2013

Spotted wing drosophila traps in strawberry plots at the Horticultural Crops Research Station, Clayton, NC. Photo: HJB

Strawberries are just beginning to ripen in central North Carolina, so last week, we placed spotted wing drosophila (SWD, Drosophila suzukii) traps in our research plots at the Horticultural Crops Research Station in Clayton, NC.  Eagle eyed observers will noticed some differences in the traps in the photo above and those we placed in our SWD plots a few years ago.

Shading traps placed in strawberries

What's easily visible above is that our traps have "hats".  We added these hats because work from other labs suggested that SWD like shade and that leaving traps uncovered in strawberry plantings may catch fewer flies.  In a multistate comparison of SWD traps conducted in 2011, a trap with a "hat", referred to as the Haviland trap, caught more flies than other trap types in a range of different crops.  Hats are likely not necessarily in crops with shaded areas or where traps can be hung directly from host plants, like blueberries, cherries, and caneberries.

A Haviland-type SWD trap with a "hat".  In this case, the hat is meant to keep rain out. The Haviland trap performed well in a comparison of SWD traps during 2011.Photo: HJB

Bait recommendations

In previous years, we have used apple cider vinegar (ACV) as the primary bait in our SWD traps and for the SWD*VMN because early experiences suggested that it was easier to work with compared to a yeast & sugar slurry (the other bait we tested).  However, these early experiences were based on changing the baits less frequently than every week.  When baits are changed weekly, yeast & sugar lures appear to catch more flies and may catch flies earlier than ACV.  Therefore, for 2013, we're suggesting that SWD trappers consider using yeast & sugar lures rather than ACV.

In order to make the yeast & sugar bait, follow the steps below:

Ingredients for yeast & sugar slurry: yeast & sugar! Photo: HJB

1. Collect the bait ingredients, active yeast and plain sugar.

2. Combine 4 Tbsp sugar with 2 Tbsp yeast.

3. Add 32 fl oz of water to the dry ingredients and stir till the mixture is suspended. Do not store premixed bait in a sealed container.  It is actively fermenting (which is what attracts flies) and can explode.  It's easiest to mix bait as it's needed rather than premixing.

4. Fill traps with 150 ml of bait (or just over 5 fl oz) each.  Traps should be check and baits changed weekly.  The odors associated with these non preserved baits change over time, and after one week, they are likely less attractive to SWD.

A few other helpful hits for using yeast traps:

• Many other insects find fermenting yeasts attractive. Traps should have small entry holes, no more than 3/16 large.  Otherwise, larger insects such as beetles, filth flies, and moths will clog traps.
• Trap contents can be poured into a container for transport back to the office or lab rather than counted in the field.
• Do not discard used bait in the field.  We do not want to make our fields any more attractive to SWD than they already are!
• Kitchen sieves can be used to filter flies, but flies in yeast baits might need be rinsed after filtering to see wings, legs, and ovipositors (key ID characteristics) clearly. 

It's very likely that our bait recommendations will change for next year, based on experiments that are planned or already underway. SWD is an invasive species, meaning it's new to North Carolina, and many other areas. Therefore, many of our monitoring and management recommendations are subject to change.  We are all learning a lot of new information, as quickly as we can!

For the time being, we have not changed our trap recommendations. We are still suggesting using 32 oz plastic containers for 2013, although this recommendation is also subject to change, especially if commercially available traps become available that out perform homemade traps.

More information
Plan to monitor insects in 2013 - NC Small Fruit & Specialty Crop IPM