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, grapes are a preferred late season host. Berry crops, grapes and cherries are at greatest risk.
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 wings. Several 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
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
insecticides. Insecticide 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 2014 Virginia
Management Guide for Commercial Small fruit, on page 2-6
(strawberry), 2-9 (caneberry), and 2-13 (blueberry). SWD is
also covered in the Commercial
Vineyard PMG (p 3-10). 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
Three materials of
differing modes of action are spinetoram, malathion and
Max). 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 and pyrethrin. Use
cultural controls to help minimize the need for insecticides.
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)
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.
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
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.