Egg Detection and Larval Sampling
Eggs and larvae of SWD may be detected in fruit. To see the presence of eggs on the berry surface, look for breathing tubes (Figure 1) and pits on the outside of the fruit.
Figure 1. Egg breathing tubes at the surface of the berry
For larval detection, place suspected fruit in a Ziploc-type bag, slightly crush the fruit (Figure 2) and add a salt water solution (1/4 cup salt/ 4 cups water). Leave the fruit in the mixture for one hour. Dislodged larvae will float. Backlighting the bag should facilitate detection. Another method is to boil suspected berries in 150 milliliters (approx. 5-‐6 ounces) of water for one minute then gently crushing the berries over a 4 mesh screen with a spoon and then rinsing the fruit under cold water with a dark tray underneath to collect the juice and larvae. The dark tray should facilitate detection of larvae.
Figure 2: Crushed fruit
To confirm that the larvae in the fruit are SWD, first collect coloring damaged fruit and place them in a Ziploc bag and let the adults emerge. When the adults emerge, place the bag in the freezer to stun the flies. The flies can then be identified or transferred to a container with rubbing alcohol and shipped to:
Insect Diagnostic Lab
Madison, WI 53706
The monitoring of SWD adults during the growing season will ensure early detection and rapid response. Trapping is a valuable technique that should be used for detection and to monitor adult population trends. Traps are available commercially but are also simple and inexpensive to make (Figure 3). Simply use a 32 oz. clear plastic deli cup with a lid. Drill or melt 10 3/16″-3/8″ inch holes (preferably 3/16″) around the top of the cup to allow adults to enter. Larger holes will allow larger insects to enter and make counting SWD more difficult. Leave ~3-4 inches without holes to allow easy pouring of the liquid bait. Traps can be baited with either ~1 inch of apple cider vinegar, or a yeast-sugar mix (1 Tbsp. active dry yeast: 4 Tbsp. sugar: 12 oz water). Add either a couple drops of unscented soap or a yellow sticky card (hung from the inside of the lid using a paperclip) to prevent flies from escaping. The soap will break the surface tension of the liquid bait and allow the flies to drown.
Hang traps in the shaded plant canopy where fruit are present. For strawberries, this may be on the ground. Place about 1 trap/acre. Check traps weekly, record catches, and replace liquid bait on a weekly schedule. Do not pour bait out at the base of the trap as it will confuse the adults and reduce the effectiveness of the trap. You can either dispose of the bait either in a bucket or on the ground away from the monitored crop. A hand‐lens (at least 30x magnification) or a microscope will be useful for identifying male SWD and required for identifying female SWD. The best detection is expected as the fruit begin to ripen.
If fruit is ripening and SWD flies are trapped, switch to checking traps at least twice per week to assess fly distribution. Use cultural controls when possible, but registered insecticides can be used from detection until the harvest is completed.
Nets may be useful to prevent flies from attacking fruit. Apply netting before the fruit begins to ripen. Secure the netting at bottom so flies cannot enter and choose a mesh size small enough to prevent the flies from entering.
2. Minimize the buildup of SWD
Minimize the buildup of SWD by removing native wild hosts such as blackberries, plums, dogwoods, and honeysuckle. Schedule timely harvests and remove over-ripe or infested fruit from the field as soon as possible to prevent the development of eggs and larvae. When collecting fruit, one suggestion is to have 2 buckets with you, one to collect good fruit and another to collect over-ripe and infested fruit.
3. Dispose of infested fruit
You can place infested fruit inside a plastic bag, seal the bag, and solarize the bag. If you have a lot of infested fruit, you can lay them on the ground in a sunny area, cover all the fruit with a piece of clear plastic, and seal the plastic with soil around the edges. You can also bury the fruit. Important note: DO NOT compost fruit!
Use traps to determine when adults are present and treat with insecticides if the crop is at a susceptible stage. A list of insecticides, that should be effective against SWD in different crops is provided below (for insecticides for a specific crop, see recommendations below). Spray in short intervals (4-5 days) to prevent crop infestation before and during harvest. Always read and follow label instructions carefully. Make sure that the insecticide you use is registered on your crop!
Two insecticides, Pyganic and Entrust, are OMRI approved. Organic insecticides are less effective than conventional insecticides. Organic production requires intensive monitoring, more timely application, and shorter intervals between sprays. Cultural controls are even more important to help reduce overall SWD population levels.
But as already observed in the west coast states, SWD population can be controlled and managed by organic growers through more intensive monitoring, cultural controls, and shorter intervals between sprays.
No biological control is available yet for SWD. Research is on the way to identify biological control agents against SWD. Hopefully, natural enemies of other drosophila species will soon have a taste for SWD!
Management Recommendation Per Crop
Blueberry – Blueberry SWD management recommendations 2015
Raspberry – Raspberry SWD management recommendations 2015
Strawberry – Strawberry SWD management recommendations 2015