Females can start laying eggs as soon as you see adults. Once the adult flies are discovered, management decisions should be made. Adult flies are tan with red eyes and a tiny 2-3mm-long (up to a one-eighth of an inch). Males have characteristic dark spots on their wings that can easily be seen with a magnifying glass. Adults live for up to 2 weeks, and females can lay up to 300 eggs. Development from egg to adult can occur in as little as eight days, and 10 or more generations may occur within a season. Illinois Natural History Survey offers more information on identification.
Hosts: raspberry, tart cherry, strawberry (after harvest), blueberry, blackberry, grape (when already damaged). As you can see, there is a wide range of commercially important, soft-bodied fruits that are impacted by the spotted wing drosophila. A compounding factor on the fly's spread is that more than 40 wild hosts have been identified, meaning the spotted wing drosophila can reproduce and spread outside commercial production.
The long list of wild hosts includes many common plants such as our native dogwood, mulberry, persimmon, pawpaw, viburnum species, as well as non-native or invasive species such as autumn olive, honeysuckle, and burning bush. For more on non-crop host plants, see Oregon State University's article on non-crop host plants.
"Spotted wing drosophila is suspected to be present in much of the state," says Kelly Estes of the Illinois Natural History Survey. Estes is the State Survey Coordinator for the Illinois Cooperative Agriculture Pest Survey Program, which monitors SWD populations throughout Illinois.
Given the widespread distribution in Illinois and the anticipation of a statewide presence, what are the implications of this pest for home gardeners? In the future, we can expect damage on all soft-bodied fruits listed above and other common garden crops with soft skins, such as tomatoes.
- Place yellow insect sticky card traps in an empty yogurt container with holes at top and apple cider vinegar at the bottom to attract the adult flies. There are professional spotted-wing drosophila traps with lures that can be to set out in large crop areas. For more information to construct traps visit see Michigan State University Extension's trap model.
- To test the fruit for larvae, leave a small portion of fruit at room temperature for a few days. Small white worm-like larvae may be seen as they turn the fruit to mush. A cup of salt in one gallon of water is an alternate way to draw the larvae out of the fruit.
Once flies are detected, use exclusion netting. Netting with 1-millimeter (0.03125 inch) mesh can be employed to help protect fruits from SWD. To be effective, netting must completely cover the plants and be sealed to the surface of the ground.
A variety of cultural practices can be used to reduce the damage from crop infestation, including removal of alternate host plants like pokeweed and wild grape, timely harvest, and removing overripe fruit.
Fruit should be refrigerated immediately after harvest. This practice will limit the growth of any eggs already laid in the harvested fruit, likely preventing the hatching of larva.
Keeping shrubs well pruned and the use of drip irrigation can limit infestation as the spotted wing drosophila prefers a humid environment.
There are effective spray treatments that can be employed if the above cultural practices are not enough. Use a spray program to reduce the chance of crop failure and inedible berries. Chemical sprays containing Spinosad and pyrethrin have been the most effective. As always, spray when bees are not out visiting the flowers and only use according to the label.