Spotted Wing Drosophila: Monitoring and Management

Published: July 6, 2015

Why is Spotted Wing Drosophila (SWD) such a concern?
This invasive insect primarily attacks blueberries, blackberries, raspberries, cherries, strawberries, elderberries, and peaches. Less preferred fruits include grapes and wine grapes, figs, boysenberries, plums, nectarines, and persimmon. Unlike other vinegar flies, SWD attacks sound ripening fruit and once eggs are laid inside fruit, insecticides will provide no control. Thus, it is imperative to control SWD before females lay eggs. Its short lifecycle and overlapping generations make spray timing difficult. An added problem is that for successful control farmers need to spray near harvest time and multiple sprays using the same insecticide class can lead to pesticide resistance. Thus, it is important to rotate insecticide classes.

2014 evaluation of commercial and home-made lures for SWD.
From late July to late October 2014 the LU IPM program conducted a field study aimed at comparing the attractiveness of a new synthetic lure (trade name: SWD Pherocon, by Trece Inc.) versus that of the standard yeast / sugar bait (home-made lure) to male and female SWD. The study took place in an unsprayed elderberry plot at the Lincoln University Carver farm (Jefferson City, MO). Traps were deployed in pairs (n= 4), about 10 ft. apart, on fruiting plants. Traps were inspected once a week and all insects captured were taken to the lab for identification. Every week, the one-week old traps were replaced with traps having new baits / lures.

Key findings:
As shown in the graphs below, the active dry yeast + sugar bait consistently out-competed the new commercial lure.

The table on the right summarizes captures across the entire season. It reveals that the standard sugar / yeast bait was on average 4.8 and 20.3 times more attractive to males and females, respectively, than the new lure. Thus, the home-made lure seems to be the most effective at this moment at detecting SWD.

Monitoring for SWD in 2015.
The first adult Spotted Wing Drosophila was captured by a monitoring trap in the Jefferson City area on May 27th, 2015. This trap was hung from a mulberry tree that has ripening fruit. Since then, SWD has been found in most locations where SWD monitoring traps have been setup by the LU / MU IPM programs. Consequently, farmers are encouraged to monitor for this insect pest Ideally, monitoring traps should be deployed starting 3-4 weeks before berry ripening and throughout the harvest season. Place one monitoring trap baited with active dry yeast (1/2 tablespoon), sugar (2 tablespoons) and water (6 ounces) per acre. The trap needs to be hang on a plant, stake, or trellis 3–5 feet above the ground on the most shaded / cooler side of the plant canopy. Because SWD reproduces so quickly under warm weather conditions, the first SWD trapping data are vital to activate pest management programs to prevent rapid population increases and potential infestations on a farm.

The process of identifying SWD: (a) view of trap with many small insects on the sticky card and in the sugar/yeast bait; (b) view of container with insects floating on clean water after sieving them from the old bait(on the right); (c) after spreading out insects onto a tray, use a paint brush or similar to split them into smaller groups, and then systematically look for small flies that have either spots on wings (male SWD, see red circle) or flies that have the egg-laying structure (shown enlarged in [d]).

For 2015, the LU / MU IPM programs will be monitoring the presence and abundance of SWD in selected locations throughout Missouri. Information will be posted weekly at the MU IPM Pest Monitoring Network website: https://ipm.missouri.edu/pestmonitoring.

SWD Management for the 2015 season.
Farmers are advised to apply an insecticide as soon as SWD is detected and fruit is at susceptible stage. Cultural controls such as sanitation (i.e., clean up and destroy over-ripe fruit) and pruning to reduce amount of foliage can help reduce breeding sites and can also improve insecticide coverage. Articles discussing the importance of SWD monitoring, how to make your own monitoring trap, management options including organic tools can be found at: http://www.LU-IPM.net. Note that the Spotted Wing Drosophila tab has a scroll down menu. Fact Sheets and Guide Sheets listing the most effective organic and reduced-risk insecticides that can be applied against SWD are available the LU IPM program website http://www.lincolnu.edu/web/programs-and-projects/ipm.