Spotted Wing Drosophila
Posted: October 10, 2011
Spotted Wing Drosophila (SWD) is a small vinegar fly that is damaging tree fruit and berry crops in the eastern United States, and can potentially attack many fruit species such as cherries, plums, peaches, some apple varieties and Asian pears, says Dr. David Biddinger, entomologist at the Pennsylvania State University Fruit Research and Extension Center. The greatest potential for damage, however, is probably to the many types of berry crops, especially strawberries, cranberries and grapes.
Native to Southeast Asia, the fly was first detected in the western United States in 2008. Recently, Biddinger was scouting in a five-acre site of late season yellow and red raspberries in southern PA and discovered that between 30 and 50 percent of the fruit was infested with SWD larvae. Unlike other vinegar flies that target damaged or overripe fruit, SWD females will attack any soft-skinned healthy fruit to lay its eggs, Biddinger explains. He reported it appeared the fruit was being infested with larvae just before the fruit ripened.
A grower from Berks County reports significant losses in blackberries, raspberries and white peaches, but the damage has not been confirmed as all coming from SWD since damage from stink bugs look similar. In addition to Pennsylvania, entomologists in Connecticut, North Carolina, Virginia, West Virginia and New Jersey are reporting SWD in vinegar traps, and some report significant fruit loss. The sustained, cool, wet weather in the eastern part of the country this season has delayed harvest of many late season crops leading to more over-ripe fruit than usual and consequently more fruit flies of all types. With over 180 species of vinegar flies in the US, it is difficult to determine if the larvae are from SWD unless they are reared to adults or traps are used to monitor SWD populations, says Biddinger.
Biddinger explains it is important for growers to be able to identify the pest and to learn about monitoring and management of SWD. Identification is key, but because of its small size and because of several similar fruit flies in our region look very similar, it can be difficult. Over a thousand fruit flies may come to a single vinegar trap with only a small percentage being SWD since many types of flies are attracted to vinegar.