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Friday, October 8, 2010

A different story at the Sandhills

After yesterday's visit to the Upper Mountain Research Station, I was eager to check my spotted wing drosophila (SWD) traps at the Sandhills Research Station today.  My first stop at the station was the caneberry breeding plots.

Caneberry seedling plots at Sandhills Research Station.  Photo: HJB
Raspberries are grown at Sandhills not because they do well here but because most raspberries cannot tolerate high heat.  The plots here are intended to screen breeding material for heat tolerance traits that will be used to develop raspberries that can be grown in hot summers.  In other words, most raspberries are not happy at the Sandhills.

We began catching SWD adults at the Sandhills on 11 August 2010 and trap captures peaked on 18 August.  See trapping data here.  Dates are in ordinal days; see here to convert ordinal days into calendar dates.  There were no blackberries present at this time, few peaches were remaining, and no larvae were found in fruit.  No flies were captured during the month of September, and one fly was caught last week.

SWD and raspberries have a lot in common in terms of temperature tolerance.  Both like mild weather and, at least according to current literature for SWD, do not reproduce in hot weather.  I suspect that the record heat this summer may have limited SWD's initial spread through North Carolina, but now as fall temperatures cool, we may see more flies and more maggots.

There were a few raspberry plants with fruit, and most of what I observed did not contain visible larvae.  I did find one, otherwise perfectly sound fruit, that contained one early instar larva.

Early instar maggot (center of image), likely spotted wing drosophila, in a red ripe raspberry at the Sandhills Research Station, Jackson Springs, NC. Photo: HJB
Because this larva was so small, I collected a sample of other raspberries from the field and will be holding these to determine if any others contain SWD larvae.

Ripe and overripe raspberries collected to determine the presence of SWD larvae at the Sandhills Research Station. Photo: HJB
 So, why do we have a large amount of infested fruit at Upper Mountain and very little (apparently) infested fruit at Sandhills?  Fruit availability differs between these two site this time of year; Upper Mountain has strawberries, caneberries, and grapes ripe and open to infestation while Sandhills only has a few remaining raspberries.  But why did the Sandhills infestation not take off when the hundreds of peach trees at the station were loaded with fruit?  The flies were not present in high numbers at the height of peach season, but I also think climate played an important role.  The Sandhills are in the hottest part of North Carolina, and peach season is during the hottest part of the year.  This may have limited the spread of SWD into the Sandhills this summer.  Now that the fly is present and reproducing, it will be interesting to see what next summer holds.  We will be there to find out.

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

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