To: Grape Growers
From: Doug Pfeiffer, Fruit Entomologist
Sent: July 1, 2011
A new invasive fruit insect pest has been detected in Virginia. I am presenting some general information here, with a link to further information.
Spotted wing drosophila: Spotted wing drosophila (SWD) is quite different from the familiar vinegar flies, other Drosophila species, that are attracted to overripe or rotting fruit material. Drosophila suzukii prefers to lay eggs in ripening fruit – the ability to do this results from the presence of a long, serrated and hardened ovipositor, unlike the small, weak ovipositor in other Drosophila spp. SWD was introduced into Hawaii several years ago and was found in California in 2008, infesting strawberries and caneberries. In 2009 it spread up the Pacific Coast to infest fruit in Oregon, Washington, and British Columbia. In 2009, it was found in Florida. In 2010, we took part in a regional trapping study (SC, NC and VA); at that time it was found in both Carolinas, but not Virginia. However, yesterday, we received confirmation of a collection in central Virginia, collected in late June. Presence will likely be determined elsewhere in the state as well, as this insect continues to extend its geographic range.
The host range includes a wide range of fruit crops: berry crops such as grapes, raspberries, blackberries, blueberries, and strawberries, but also tree fruits – apples, cherries, nectarines, peaches, pears, and plums. While cherries are a preferred early season host, grapes are a preferred late season host.
Larvae are similar to larvae of other Drosophila vinegar flies, tiny maggots about 3 mm long. Larvae feed beneath the skin of the fruit, causing a collapse of tissue near the site, followed by invasion of molds. Losses ranging from 33-100% of the fruit have been reported. An important management problem has been that this species attacks the fruit during final ripening, and can escape detection as grower think they have ended their spray season. Fortunately, this insect is not as difficult to kill as our other important invasive pest, brown marmorated stink bug. However, diligence is needed to determine the need to spray.
Apple cider vinegar traps can be used to determine presence of the fly. Other Drosophila spp may look very similar, and care is needed to make a proper identification. Inspect fruit frequently during ripening for small oviposition scars and presence of larvae beneath the skin. Rotate materials of different modes of action, to delay the development or resistance. Harvest fruit promptly, and prevent continuing presence of overripe fruit.
I have posted a SWD page in the Virginia Fruit web site, in each of the fruit crop sections (http://www.virginiafruit.ento.vt.edu/SWD.html). Further updates on this new invasive pest will be posted here.