Monitoring for Spotted Wing Drosophila Print E-mail
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Basic instructions for ‘Wet Traps’:

Bait is needed to attract the flies to the trap. Apple cider vinegar (sometimes called just ‘cider vinegar’) is easy and cheap, but yeast-based bait solutions may catch more SWD flies. Both baits will catch other vinegar/fruit fly species as well. Yeast recipe: 2 teaspoons baker’s yeast, 4 teaspoons sugar, 2 cups water; mix this up the night before it is used; it will fill 4-5 traps. A small yellow sticky card can be hung or wedged in the trap container to catch flies.

Place traps when temperature is consistently over 10oC (50oF), and/or when fruit starts to form. Hang traps in plant canopy, or set firmly in the ground within the plant row, in a shady location. Put one trap in a sunny location, just in case.

Check traps at least once per week. Look for the spotted wing males in the bait solution, and on the sticky cards. Use a hand lens, or a jeweller’s lens, or an optivisor, or a magnifying glass for better viewing if desired. Count and record the number of male flies on a data sheet. Replace the bait solution and sticky card at least each week. Dump the old solution away from crop plants.

Basic instructions for ‘Sweep Netting’:

Basic instructions for ‘Fruit Collection’:

Near or during harvest, collect about 1 cup (250 ml) of ripe fruit from field or harvest bins from an area of interest. Raising flies: In the lab, lay fruit out one layer deep in a flat container, cover with mesh or loosely with a lid. Air circulation is important, as larvae will suffocate if the container is sealed. Keep containers at room temperature (22oC) for up to two weeks, or until all the flies have emerged. Container and flies can then be put in the freezer. Frozen flies can be viewed for spotted wings. If you wish to keep the flies, put in 70% ethanol (alcohol). *Note that male flies do not get their spots until several hours after emergence. Floating out larvae: larvae can be ‘floated out’ of mushed berries in sugar water (see info in Oregon State links).


Each method has its benefits and drawbacks as discussed in the table below. Monitoring Tool

Pro

Con

Sweep Net

Give a quick answer: can identify if SWD flies are present right in the field

Need to be selective in the areas that you sweep (i.e. You need to see the flies or choose a risky place, like over the cull piles or on overripe hanging fruit. May not be good for detecting the ‘first fly’ of the year.

Wet Traps

Can keep track of changes in fly numbers over the season. Can more likely detect the ‘first fly’ of the year. Easy to use systematically (i.e. Check once per week).

Takes a several days (~1 week) to find out if SWD are present (or as long as your interval between trap-checking is).

Fruit Collection

Best way to confirm if SWD is infesting fruit

Cannot detect SWD presence before harvest. Takes up to two weeks to raise flies for identification.

Fruit Collection

Quickly confirms if larvae are in fruit.

Cannot identify to species from larvae only, but most vinegar/fruit flies in sound fruit will be SWD (however, if fruit is damaged, other species could be present).

Sweep where flies are seen within plant rows, over cull piles, dropped fruit, or in the plant canopy where there is ripe/over-ripe hanging fruit. Make 10 passes with the sweep net for one sample. Net contents can be shaken into soapy water to disable flies, or bag flies directly (some may escape). Other vinegar/fruit fly species will be caught in addition to SWD. Male SWD flies can be identified and counted in the field, or taken to the lab or central collection site to be counted. Traps can be made of any 250-750 ml plastic container that has a tight fitting lid. About four holes 0.5 cm in diameter need to be made in the top or side of the container to allow flies to enter (holes shouldn’t be too big or predatory beetles and other large insects and slugs can get in). Containers that already have holes, like commercial vinegar/fruit fly traps, or large spice containers will work. Holes are best placed in the side of the container so that rain doesn’t get in.

 

 

 

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