Spotted Wing Drosophila in Cranberry: Is this an Issue?

Here is an article from the Wisconsin State Cranberry Growers’ Association newsletter about recent research in the Steffan lab:

Cranberries and spotted wing Drosophila (SWD) in Wisconsin

Shawn Steffan (USDA-ARS Madison, WI), Jana Lee (USDA-ARS Corvallis, OR), Laura Lavine (Washington State University), Doug Walsh (Washington State University), Chase Metzger (Washington State University), Juan Zalapa (USDA-ARS Madison, WI), Christelle Guédot (University of Wisconsin-Madison), and Phil Pellitteri (University of Wisconsin-Madison).

This holiday season, there will be one demographic that won’t want to eat fresh cranberries: spotted wing Drosophila maggots. Drosophila suzukii, commonly known as SWD, does not appear to like cranberries very much. Following multiple replicated trials using ripe, under-ripe, and over-ripe organic Wisconsin cranberries, SWD females would not (or could not) insert eggs into under-ripe or ripe cranberries. This suggests that healthy, current-year fruit should be safe from attack.

Scaptomyza (Drosophilid)

Among the over-ripe, decaying cranberries (harvested, frozen, thawed, refrigerated) just two eggs were found among many berries, but no mature larvae were detected, and no adults emerged. Fortunately, rotting fruit don’t make it into the harvest because they generally don’t float. Decaying fruit get devoured every spring and summer by other drosophilid flies (see photograph above), various beetles, and countless hordes of mites and springtails.

While none of the SWD larvae successfully developed within the highly acidic flesh of fresh cranberries, studies using physically damaged cranberries showed that SWD could develop to adulthood. Again, these berries represented wounded, decaying fruit, not the sort of berries that would get harvested. That said, SWD populations could build within cranberry beds and potentially play a role in regional source-sink dynamics.

Unfortunately, SWD females love blueberries and raspberries—this we learned early. The good news for cranberry growers is that SWD adults have only rarely been trapped in/near cranberry beds, and in these cases, a blueberry or raspberry patch was nearby.

So, the take-home message: current-year cranberries (that aren’t damaged and/or rotting) appear to be safe from SWD attack. Conversely, last-year’s decaying bounty of unharvested cranberries may be vulnerable. SWD populations will likely be found each spring and summer in fruit-growing regions, but the risk to cranberry production seems minimal.

If you are suspicious of any infested fruit, contact your local Extension agent.

For other fruit crops, here is a list of resources that may be helpful:

University of Wisconsin Extension has released an article on Spotted Wing Drosophila, Drosophila suzukii, with several suggestions for scouting and trapping the fruit flies.

University of Wisconsin-Madison has a website about the Spotted Wing Drosophila in Wisconsin.

The University of Minnesota and Michigan State University have web pages with extensive lists of resources including a map of counties with SWD in Minnesota and Wisconsin.

North Carolina State University’s Small Fruit and Specialty Crop IPM blog

Pacific Northwest Insect Management Handbook SWD page

–Liz Bosak