by Marilyn Odneal, Horticulture Adviser
(Mountain Grove) – The spotted wing drosophila (SWD), Drosophila suzukii, is a small fruit fly that is a big threat to many of our fruit crops. SWD was first discovered in the western United States in 2008 and was first detected in the Eastern U. S. in Michigan in late September of 2010. Researchers in Arkansas have found this pest in traps this summer.
Vickie Baumer, a graduate student intern, has trapped this pest at the Missouri State Fruit Experiment Station at Mountain Grove this year using a yeast-baited trap with a vinegar and white wine drowning solution. Specimens have been identified in our blackberry and primocane raspberry plantings. There is also a trap in the blueberry planting. Once the grapes begin to ripen, we will put some traps in our vineyards as well.
The spotted wing drosophila can damage blueberries, raspberries, blackberries, strawberries, cherries, grapes and other soft skinned fruit. Unfortunately, the SWD actually damages perfectly healthy fruit when the female flies cut a slit and lay eggs under the skin. Regular fruit or vinegar flies only lay eggs in damaged, overripe or fermenting fruit.
The flies are small, so we identify them under a binocular microscope. One of the key characteristics of the male is the spots on the wings and one of the key characteristics of the female is the saw-like ovipositor or egg layer.
The larvae that hatch from the SWD eggs look like short white worms and can be in ripe fruit after harvest. The egg-laying slit allows sour rot and other fungal diseases to enter the fruit, further damaging fruit quality.
The adult SWD lives for about two weeks and can lay more than 300 eggs. There can be many generations of this pest in a season. Infested fruit do not show obvious symptoms at first, but the fruit will begin to break down within a few days. By this point, the white larvae can be relatively easy to detect.
Since this is a new pest, a lot of research is being conducted to determine how to manage it in our small fruit and grape plantings. Keeping your plantings at home well picked – both good fruit and damaged fruit – is important. In our primocane bearing raspberries, we will pick the overripe and damaged fruit and put it in a plastic bag, seal it and put in the sun in order to kill the larvae. We will harvest the sound fruit and check a sample of it for larvae by putting 70 berries in one quart of water with one cup of sugar and a little dish detergent. The larvae should float to the top in about a half an hour.
For further information on this pest, check the University of Arkansas Bulletin “Biology, Identification and Management of Spotted Wing Drosophila” here.
Please direct comments or questions concerning this column to Marilyn Odneal via email at MarilynOdneal@missouristate.edu; write to Missouri State Fruit Experiment Station, 9740 Red Spring Road, Mountain Grove, Mo. 65711; or call (417) 547-7500. Visit our website.