Spotted Wing Drosophila Spotted Again


Curtis Young reported that the spotted wing drosophila (Drosophila suzukii) (SWD) is back again in Van Wert County.  At the original location where the first detection of SWD in Ohio was made in 2011, it is again damaging fall red raspberries on the cane.  It is also attacking grapes, blackberries, peaches and other fruit grown on the property.  Tim Malinich in Erie County is awaiting confirmation of the insect's presence there as well.  Reports of SWD being in several other counties in the central Ohio area have also been registered.

At the original find location, attention to SWD's presence came when ripening raspberries turned to mush on the cane.  And that's one of the big problems with SWD, it attacks fruit before it is ripe and those fruits will be ruined before they can be picked or will quickly spoil shortly after being picked (i.e. produce has no shelf-life).  Close inspection of damaged/spoiled fruit reveals numerous small, white maggots in the flesh of the fruit.  The fruits that can be damaged in this manner produce a long list.  Obviously, raspberries and blackberries are high on this list, but so are grapes, both wine and table grapes.  There are also some reports that fresh market tomatoes are under attack.  Suspicions that SWD may be in many other Ohio counties are arising especially where produce in farmers' markets and roadside fruit stands are deteriorating uncommonly fast. 

The reason SWD can attack fruit while it is still ripening is the female's ovipositor (egg laying device) is very large in comparison to other fruit (vinegar) flies and serrated (it has rows of sharp, hard teeth).  With her ovipositor, she is able to penetrate the skin of soft-skinned fruit and lay eggs just under the skin, creating a small depression ("sting") on the fruit surface.  Each clutch of eggs is from 1-3, and the female will oviposit into many fruits.  Multiples of larvae (maggots) within a single fruit are quite possible because many females may visit the same fruit to oviposit.  Once fruit begins to deteriorate, it can be attacked by other common fruit (vinegar) flies (i.e., Drosophila melanogaster).  Additionally, the damage from SWD can provide an entry site for infection by secondary fungal and bacterial pathogens, but this is not always the case.