A New Threat to North American Fruit: Spotted Wing Drosophila
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If you grow or are considering growing cherries, strawberries, mulberry, plums, peaches, apricots, nectarines, Asian pears, currants, blackberries, loganberries, raspberries, marionberries, blueberries, grapes (both table and wine), kiwi (regular and hardy), persimmons, loquats, figs or any other soft-bodied fruits please read the following information.
THREAT AND DISTRIBUTION Spotted Wing drosophila (SWD) is a new pest in North America that has been imported from the far east and most experts put the region of origin as China or possibly Japan. It was first confirmed in California in 2008 and by 2011 has been confirmed up and down the entire west coast. It next appeared in Florida in 2009 and by the end of 2011 SWD presence has been confirmed in Washington, Oregon, California, Wisconsin, Michigan, Ohio, Pennsylvania, Maryland, Hew Hampshire, Vermont, Connecticut, New York, Virginia, North Carolina, South Carolina, Louisiana, Florida and Utah, in Canada British Columbia, Alberta, Ontario and Quebec In 2012 SWD is expected to be found in wider distribution in the states listed above as well as surrounding states.
GENERAL DISCUSSION SWD is classifie d as a vinegar fruit fly and is in the family of drosophila of which there are about 175 different flies. Of this number SWD is basically the only one that infest, by choice, sound and healthy fruit. It will attack ripe fruit but will also infest most fruits just as they enter the first stages of ripening through completely ripe and beyond. The potential for damaged crops in areas where SWD is present is high and this past year damage has been reported to have ranged from insignificant in new infestation areas and 20% to 80% or more loss in moderate to high infestation areas. In many areas the SWD presence was unknown until harvest and by then the larvae were in the fruit; once that happens, the infected fruit is lost..
Part of the problem with SWD is simply a lack of education on this threat. In the fall of 2011 I attended a field day conducted by NCSU on small fruits. With about 100 growers from commercial to backyard gardeners present. Fewer than 10% had heard of SWD and North Carolina is one states in which SWD has a moderate presence. Many infestations has simply been misidentified
SWD is a severe infestation risk. In controlled studies one female can in one month produce a population of 10,000+ females and a comparable number of males flies. The time from egg to adult can be as short as 9 days!
IDENTIFICATION AND CONTROL SWD looks, at first, like just about any other drosophila but, can be distinguished readily by identifying the male which has a black spot near the tip of each wing.
The males are almost always found in traps with females, which are harder to identify, and can be used as a measure of the presence of SWD.
Traps can be baited with cider vinegar with one or two drops of non-fragrance dish soap on top which will help to drown the flies, or you can use one tablespoon yeast, four teaspoons of sugar and 12 ounces of water as the attractant. Once identified, use your developed spray program and stick with it and do not miss or skip by even one day. SWD has in many ways caught this country off-guard and many states have issued emergency acceptance of insecticides that have shown the ability to control SWD. For the home gardener these include Pyrethrins like Pyganic, Spinosad like Entrust or Success, and Malathion. It is of vital importance that you follow established application rates, pre-harvest intervals(PHI), and re-entry intervals(RHI). It is also of great importance that you use more than one insecticide in rotation to prevent SWD from immune to the effects of any one class of material. SWD has been shown in lab studies to quickly gain resistance and immunity to insecticides like pyrethrins.
ADDITIONAL INFORMATION More information can be found by typing "Spotted Wing Drosophila" into any web browser. Please be aware that there is a lot of information that has been translated from Japanese and that many of the practices and materials that are successful there are not bearing out as true in North America. This is causing some contradictory information on the web. Your best source of information for local conditions and status will be your local Cooperative Extension Agent. Your Extension Agent will have access to local university information and will be an invaluable resource for you. If you are asked to be part of a monitoring network, please allow them to do so on your property.
FINALLY SWD is here to stay and will, in general, get worse in many areas. The wild fruit we have enjoyed for hundreds of years is now at risk and in many parts of the country will now be lost due to high infestation rates of SWD. If you want to enjoy home raised fruits from now on you MUST get educated on SWD and protect you crops. SWD has already adapted to temperatures and conditions that should have slowed it down and it has only been here 3-4 years so, we must be vigilant for it's continued adaptations.
Image of male drosophila courtesy of John Davis
Life cycle chart courtesy of Colleen Burrows, Agriculture Special Projects coordinator, Washington State University, Whatcom County Extension and Beverly S. Gerdeman, Ph.D. Washington State University Research Associate, Entomology International Programs Project Associate, USAID IPM CRSP WSU Mount Vernon Northwestern Washington Research and Extension Center and used with their permissions.