Spotted Wing Drosophila Detected – Jim Jasinski, OSU Extension IPM Program, Celeste Welty, Dept. of Entomology.
Spotted wing drosophila (SWD) flies were detected in apple cider vinegar baited traps at two berry farms on July 3rd, in Clinton and Greene counties. This new species and its relatives are commonly called fruit flies or vinegar flies. This new invasive pest was first found in OH in September 2011 and was found at several Ohio sites in August 2012. Unlike the common fruit fly that is found on over-ripe fruit, the new species attacks ripening fruit ofmost berry crops such as raspberries, blueberries, blackberries, grapes, cherries, strawberries, as well as peaches and apples. Berries infested with SWD will begin to break down and mold within a few days.
To detect this fly we have deployed a network of apple cider vinegar baited traps in seven locations across the state in berry crops. To date these are the first SWD reported in 2013.
The threshold for SWD is one fly, meaning once a SWD is confirmed at a location, all susceptible ripening crops should be protected using an insecticide spray weekly through final harvest. Various insecticide options are listed on page 2 of the general Ohio SWD fact sheet posted at this link on the internet. Other management options are sanitation by trying to remove old or dropped berries and mechanical control by row covers or screening. Because the threshold is so low, early detection is essential. There are two methods to detect SWD: using an apple cider vinegar baited trap to detect the adults, and using a salt test to detect the larvae (maggots) in the fruit itself. Methods are outlined at the links posted here for assembling the baited traps to detect adults and here for using the salt test to detect larvae. If growers want to determine if SWD larvae are in the fruit, then using of the salt test is the easiest way to detect this pest, as the tiny maggots will leave the fruit and float to the top of the bag or tray.
Growers should be aware that if an apple cider vinegar trap is put up on a farm, it will catch various kinds of fruit flies; this means that the samples will have to be sorted to properly identify WHETHER OR NOT the SWD is in the sample or not. These flies are very small and must be examined carefully to identify them. The males can readily be detected by the “spot” on their wing which is visible to the naked eye, but it takes a very high power hand lens(30x) or a dissecting microscope to identify the female SWD with her heavily serrated ovipositor; the female does not have spots on the wings. In other words, just because fruit flies or vinegar flies are in the trap does not mean you should begin spraying!