SWD Trapping: Week 1

Spotted wing drosophila trap kits were sent to volunteers on Tuesday last week (April 27th) and should be placed in the field by this coming Tuesday (May 4th).  I placed our first SWD at the Horticulture Crops Research Station Ideal Track, near Castle Hayne, NC on April 23rd in my recently planted blueberry block.  Our plants are sizing up nicely, and this block is situated in 1.25 total acres of blueberries.

A yeast-sugar lure baited SWD trap at the Ideal Track.  Note the yellow sticky card suspended in the trap.  I forget to include these last week when I placed the traps, and I am interested to see if I will catch many more flies with their addition.  Oregon researchers have found the addition of sticky cards very effective.

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An apple cider vinegar baited trap at Ideal.  We are comparing these 2 lure types to see which is the most efficient at initially detecting SWD in the southeast and which is better for monitoring active populations (once the fly is detected).

Today, I checked these traps for the first time, and I was pleased to find no SWD in any of the traps.  I did, however, find several insects which could be confused with SWD when our 18 other locations begin to collect samples.  The traps contained fewer non-target insects than I feared they may, but this may be a function of the trapping location.  North Carolina's blueberry plantings are primarily in acidic soil, often surrounded by pine forests, and these areas may not be the most diverse habitat for fruit feeding insects.  I suspect that as the summer progresses, however, we will catch more non target insects, particularly muscid and calliphorid flies, which in my past experience really like yeast lures. (An olive fruit fly (Bactrocera oleae) trap in California I was maintaining near a horse pasture completely filled up with face flies in 1 week...so much that I couldn't tell there was liquid remaining in the trap!)

So, if I didn't find any SWD, what did I find?  I found what appears to be 2 species of native Drosophila and one species of Tephritid, or a "true" fruit fly.  Both of these groups have characteristics that may result in confusion with SWD, so I took a few photos to help trappers and other interested parties distinguish them.  I have not keyed these other flies out to species yet, but I will update this blog post with that information once I do.

The image below shows the 3 types of flies together.  On either outer side are the female tephritids.  These flies are much larger than SWD and have clearly visible, syringe-like ovipositors (egg-laying devises).  There were no males of this species in the traps this week.  The tephritids could be confused with SWD due to the prominent spots on the ends of their wings.  Remember, however, that female SWD do not have spots on their wings (only the males have spots), so an ovipositor and spots do not go together. 

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Flies found in monitoring traps on May 3, 2010.  

The 2 other Drosophila species captured included both male and female flies.  These flies were closer in size to potential SWD, but upon observation of the females under the microscope (at about 10x magnification), it was clear that they lacked the large, serrated blade-like ovipositor of female SWD.  Volunteer trappers, your SWD voucher specimens are an invaluable comparison tool for identifying females.  Use them!

A non-SWD female from monitoring trap (top) and a voucher SWD female (below).  Note the difference in ovipositor size and appearance, even at this low magnification (about 5x).

A few other helpful hints for volunteer trappers:

1. 12 oz appears to be sufficient liquid for 1 week.  I did have to refill all of my traps today (water added to the yeast-sugar lure and more apple cider vinegar added).  We will change lures every 4 weeks, so just refill for the first 3 trap checkings.  This means you will all likely need more vinegar sooner rather than later.  Contact me for refills.
2. Remember to use 2 different filter containers, one for each lure.  We do not want to cross contaminate.
3. If non-target insect numbers remain low, in-field trap check time is about 20 minutes for 6 traps.
4. I suggest changing your sticky card last--after filtering your lure and placing your insects of interest in alcohol.
5. There's no need to save beetles or moths in alcohol for ID in the lab...we know they are not SWD.

Finally, once all of our trappers have a week of data in, we will be posting live updated graphs of trap captures.  I will link these graphs through this blog.  Look for them the week of May 10th!



Sponsored by the Southern Region Small Fruit Consortium, Project 2010 E-01.