Raspberries: Spotted Wing Drosophila

The spotted wing drosophila is a vinegar or fruit fly of East Asian origin. Unlike other fruit and vinegar flies, which lay their eggs on past ripe or rotting fruit, they lay their eggs inside fresh fruit, often before harvest. Aside from the superficial scars left by the female’s ovipositor (their egg-laying device), most damage is done by the larvae feeding inside the fruit.

After only a few days, the fruit skin becomes dimpled or wrinkled, forming craters in the fruit, and making it susceptible to decays and rots. It is possible, however, for early-stage larvae or eggs to leave no visible impact on the fruit.

Fresh raspberries sitting in sugar syrup. There are small, white larva floating near the surface of the syrup, approximately as long as 1-2 raspberry drupelets.
Spotted wing drosophila larvae rise to the top of the water when fruit are macerated.
Raspberry on bush, with two small flies sitting on fruit surface. The fly on the left is viewed from the side. It has big red eyes and a humpback appearance. The fly on the right is viewed from above and appears slightly smaller. Two spots are present on the lowest point of the wings of the right insect, one at each wing bottom.
Adult female (left) and adult male (right) on
raspberry. Photo: Hannah Burrack, NC State Univ.
Close-up of inside of raspberry fruit. There is a small, squiggly, white larva curled up amongst the drupelets.
Larva inside raspberry. Photo: Hannah Burrack,
North Carolina State University
Raspberry bush with three ripe fruits. One of the raspberries is barely hanging on to its receptacle. The upper drupelets appear to be liquefying and becoming soft, causing the berry to detach from the receptacle.
Infested raspberry

More information:

Male SWD have one dark spot on the distal upper section of each wing, and two dark comb-like structures on each foreleg. Female SWD have no dark spots on wings, and have saw-like serrations on ovipositor. Male SWD can be identified without a microscope because of the distinctive spot on each wing.
A guide to visual identification and gendering of spotted wing drosophila, courtesy of M. Hauer