Spotted-Wing Drosophila, Drosophila suzukii (Matsumura)

I. Introduction: Spotted-wing drosophila (SWD), Drosophila suzukii (Matsumura), was introduced into Hawaii several years ago (Lehnert 2010).  It was found in California in 2008, infesting strawberries and caneberries (Bolda et al. 2009, Lehnert 2010).  In 2009 it spread up the Pacific Coast to infest fruit in Oregon, Washington, and the Fraser Valley of British Columbia.  Furthermore, in 2009, it was found in Florida (Acheampong 2010, Lehnert 2010), where it was found in feeding lure traps 3 miles apart, and in 2010 it was found in South Carolina, North Carolina (Burrack unpubl.) and Michigan (Milkovich 2010).  In 2011, it was found in several locations in Virginia (Pfeiffer and Maxey, unpubl.) and in New Jersey and Pennsylvania. It is now considered generally distributed in Virginia; see the distribution map for Virginia linked here Recent trapping data are reflected in the Spotted Wing Drosophila Volunteer Monitoring Network, organized by North Carolina State University, and in the map linked here.  It has been found north into Ontario.  Infestations have been associated with sour rot in French vineyards.

II. Hosts: Hosts include apples, blackberries, blueberries, cherries, nectarines, peaches, pears, plums, grapes, raspberries, and strawberries (Bolda et al. 2009, Acheampong 2010).  While cherries are a preferred early season host, caneberries are at high risk, and grapes at moderate risk.  Grapes may be ulsed as a late season host.  Berry crops, grapes and cherries are at greatest risk.

III. Description:  Females have a large serrated ovipositor, unusual among the drosophilids.  This atypical ovipositor is illustrated in several fact sheets (Acheampong 2010, Walsh et al. 2010).  In females of native drosophilids, the teeth on the ovipositor are apparent, but the structure appears less developed and overall sclerotization is less pronounced.  In some images, the ovipositor is shown exerted, but at rest it is nestled beneath the tip of the abdomen.   Males have a characteristic black spot near the ends of the wingsSeveral traits useful for identification of SWD, and several similar-looking species, are shown in a factsheet from Michigan State University.  Larvae are translucent maggots 2-3 mm long, with black mouth hooks visible at the anterior end.  Silvery white tracheal tubes may be visible through the dorsal cuticle with magnification.  Respiratory projections are present on the posterior end.

Images of SWD life stages:
    Adult female
    Adult male

IV. Biology: In eastern Asia, there are up to 13 generations.  A life cycle can be completed in 8-14 days, but adults can live up to 9 weeks.  Females use the atypically large ovipositor to lay eggs in fruits as they are ripening, earlier than other drosophila species.  Eggs are inserted under the skin of ripening fruit; each female lays 7-16 eggs/day. (See YouTube video showing oviposition behavior)  Long respiratory horns project from one end of the egg.  These horns may be found projecting from oviposition sites with magnification.  Eggs hatch in 1-3 days, and larval feeding on the flesh causes a collapse of localized tissue after another 2 days, followed by growth of fungal or bacterial organisms; yeasts may be carried on the ovipositor (Walsh et al. 2010).  Larvae are slender white maggots; pupae are brown, about 3 mm long, with two small respiratory horns protruding from one end.  A circle of bristles surrounds the tip of the pupal respiratory projection.

V. Injury: Cherries were reported to have 70-80% injury by SWD, with eggs laid in sound fruit (Demerc (1965)).  Crop losses of blueberries, caneberries and cherries have been reported ranging from 33-100% (Lehnert 2010).  SWD has been found attacking wine grapes following veraison (see photo by Christine Vrooman).  Berries may take on a shriveled, shrunken appearance, with small maggots feeding in the interior.  The respiratory horns typical of drosophilid eggs may be seen in grapes as they approach harvest; see photos by Meredith Shrader of oviposition sites in Petit verdot and Viognier.

VI. Monitoring: Trap using bait of either yeast or apple cider vinegar may be used for monitoring.  Traps using apple cider vinegar alone are attractive and less odorous to work with than with yeast added; traps with added yeast may be somewhat more sensitive, but fluid should be replaced with each service of the traps..  Instructions for construction of simple plastic cup traps are presented by Walsh et al. 2010.  A trapping guide has been posted by Oregon State University.  Traps should be checked at least weekly.  Most of the Drosophila flies collected will not be SWD, so the flies collected must be checked carefully.  Male SWD have a characteristic black spot at the tip of the wings.  Females lack this spot, but are slightly larger than other females, and have the large ovipositor mentioned above. These markers are shown in the MSU factsheet.

VII. Control:  Chemical control:  Control measures are directed against the adults; there are no effective controls for larvae in the fruit.  As vulnerable fruit approach ripeness, weekly spray applications should be made.  When using organic materials, shorter spray intervals will be needed because of the shorter residual life of botanical insecticidesInsecticide with different mode of actions should be rotated in order to delay the development of pesticide resistance.  Organophosphates (malathion and phosmet) are effective (check labels for registrations on specific crops), as are pyrethroids (be wary of induction of secondary pests).   Spinosyns offer an additional mode of action class, with spinetoram having greater efficacy than spinosad.  See the linked table for a selection of materials available on the most vulnerable crops.  Included are the maximum number of applications (or amounts of material) allowed per season.   This is important in designing rotations - it will be helpful to conserve materials effective against SWD until properly timed for that pest.  Recommendations are included in the 2017 Virginia Tech Pest Management Guide for Commercial Small fruit, on page 2-9 (strawberry), 2-17 (caneberry), and 2-23 (blueberry).  SWD is also covered in the Commercial Vineyard PMG  (p 3-9).  If SWD needs to be controlled in a vineyard setting, it will helpful to make an application just before berries close in clusters, since many oviposition points are in the protected inner surfaces of the cluster.  So far, Surround has been used for this purpose experimentally; research is planned on additional options.  When designing a chemical control program for SWD, it will be critical to rotate among different mode of action classes, but also to consider the maximum number of applications per season of each insecticides.  The latter issue includes applications applied before SWD becomes active or the host fruit become susceptible.  See this table for available SWD materials with preharvest, mode of action, and maximum allowed applications.   Organically approved treatments are included in the links provided; the number of organic tools is limited however, and management in organic berries will be a challenge.

Three materials of differing modes of action are spinetoram (Delegate and Radiant), malathion and zeta-cypermethrin (Mustang Maxx).  Malathion is registered on grape, caneberries, peach and nectarine, but not on cherry or apple.  The flowable formulation of malathion is safer than the EC formulation, but the flowable formulation may be in shorter supply.  When using the EC (oi-based) formulation, use caution if also applying the fungicide captan.  The oil can act as a penetrant, potentially causing harm to te vine (see Rutgers fact sheet on captan and oil).

In 2011, apparent tolerance to pyrethrin developed after repeated application in Oregon.  It will be important to rotate insecticides of differing modes of action in controlling this insect.  The two main organic options are spinosad, pyrethrin and kaolin.  Use cultural controls to help minimize the need for insecticides, such as open pruning to improve air circulation, and prompt and thorough harvesting.

The following links may be used for chemical control recommendations:
Spray Bulletin for Commercial Tree Fruit Growers (html)
Pest Management Guide for Commercial Vineyards (html)
Pest Management Guide for Commercial Small Fruit (html)
Pest Management Guide for Home Fruit (html)

Cultural control: Harvest fruit promptly to eliminate breeding sites.  This issue should be kept in mind once SWD established in an area, since at times grape growers may leave berries in the vine to allow greater development of some harvest parameters.   Any overripe or rotten fruit nearby should be destroyed.  In vineyards, pomace produced during the crushing process should not be dumped near the producing vineyard block.  This can become a source for many SWD.

VIII.  Larvae in your berries or cherries?
With head capsule:
    With legs: Caterpillar - cherry fruit worm, cranberry fruitworm, or oriental fruit moth
    Lacking legs:  Plum curculio

Lacking head capsule:
    With respiratory projection on hind end, tapering at both ends, 2-3 mm long: Spotted wing drosophila
    Lacking respiratory horns, tapering at front end, broad at rear end, 5-6 mm long: Cherry fruit fly, blueberry maggot

IX.  An additional exotic drosophilid!
In September 2012, an additional exotic drosophilid was found to be common in some vineyard blocks.  The African fig fly, Zaprionus indianus is originally from Africa but in recent years has been expanding its range.  From Brazil it moved northward, and was found in Florida in 2005 and South Carolina in 2007.  When present, concurrent infestation with SWD generally existed.  However in one block, Zaprionus was far more common than SWD.  At present it is unclear whether fig fruit fly can successfully oviposit in intact grape berries.  This fly is red-brown in color, with longitudinal white body stripes, thinly bordered by black.  See adult flies in dorsal and oblique view.  This fly is also described in a recorded presentation linked here.

X.  Additional reading:

Updated 4 January 2018
Maintained by: Douglas G. Pfeiffer
Department of Entomology
Virginia Tech
, Virginia
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