DROSOPHILA SUZUKII, OR SPOTTED WING
DROSOPHILA, RECORDED IN
SOUTHEASTERN PENNSYLVANIA, U.S.A.1
P. J. Freda2and J. M. Braverman3
ABSTRACT: Collections of Drosophila and their relatives were performed using bait traps on the
campus of Saint Joseph’s University, in Philadelphia and Lower Merion, Pennsylvania, between July
and December 2011 and continuing in March of 2012. In the 2011 collection season, more than 200
specimens of Drosophila suzukii (Matsumura), or spotted wing Drosophila, were collected. In 2012,
specimens started to appear in June and were collected until December. The appearance of D. suzukii
in the Philadelphia and surrounding area has severe, negative implications for local agriculture. D.
su zukii, unlike most other Drosophila species, is an agricultural pest that lays its eggs in soft-skinned,
unspoiled fruits like cherries, grapes, and berries (Bolda et al., 2009).
KEY WORDS: Drosophila, suzukii, non-native, invasive, agriculture, agricultural, pest, Philadel -
phia, Pennsylvania, U.S.A.
The goal of this study was to survey Drosophila biodiversity in the Phila del -
phia area over time. Previous work in this field discovered a number of species
inhabiting the local area including D. simulans, D. robusta,D. affinis,D. busckii,
D. putrida, D. tripunctata, and D. melanogaster, with D. simulans being the most
prevalent (Roy 2009). The collection data from 2011 and 2012 is in concordance
with the previous study but with the addition of a new, invasive species: D. su -
zukii (Matsumura), or spotted wing Drosophila. The purpose of this report is to
inform local fruit growers, researchers, and other interested parties of the pres-
ence of D. suzukii in the Philadelphia area and Northeastern U.S.
Most species of the genus Drosophila lay eggs in rotten, spoiled fruits and veg-
etables and thus do not affect growing crops. D. suzukii, however, lays its eggs
in unspoiled, soft-skinned fruits including berries, cherries, and grapes (Bolda et
al., 2009). Due to the egg-laying method of D. suzukii, the potential for substan-
tial crop loss may be great. Yield loss estimates vary widely, with negligible loss-
es in some areas and close to 80% loss in others, depending on the crop and loca-
tion (Caprile et al., 2011).
Female D. suzukii have a large, hardened, serrated ovipositor with dark teeth
that is used to cut through the skin of fruit (Vlach 2010). Fruit with oviposition
scars may be indicative of D. suzukii larvae present. Male D. suzukii are easily
identified by the presence of wing spots centered on the first major wing vein
(Vlach 2010). Additionally, male D. suzukii have a pair of sex combs on each
Volume 123, Number 1, May and June 2013 71
1Received on July 3, 2012. Accepted on December 28, 2012.
2Department of Biology, Saint Joseph’s University, 5600 City Avenue, Philadelphia, Pennsylvania
19131, U.S.A. Email: firstname.lastname@example.org
3Department of Biology, Saint Joseph’s University, 5600 City Avenue, Philadelphia, Pennsylvania
19131, U.S.A. Email: email@example.com
Mailed on July 18, 2013
front leg and unbroken bands at the end of each abdominal segment (Vlach
2010). Females lack wing spots but also have unbroken bands at the end of each
abdominal segment. The main distinguishing feature of the female is the ovipos-
itor. Both male and female adult D. suzukii are approximately 2-3 mm in length
and have light yellow or brown bodies with red eyes (Vlach 2010).
Damage to fruit is caused by both the oviposition of the female and by the lar-
vae feeding. The initial oviposition site begins to take on a sunken appearance
and is subject to decay and secondary infection. After the larvae become larger,
breathing holes are cut into the side of the fruit which further exacerbates decay
(Beers et al., 2010).
The geographical range of D. suzukii has increased dramatically. The species
was first described by Matsumura in 1931 and was widely observed in Japan,
Korea, and China in the early 1930s (Kanzawa 1939). By the 1980s, D. suzukii
was observed throughout Hawaii and first appeared in North America in Cali -
fornia in 2008 (Walsh 2009). D. suzukii has been moving east, being ob served as
far east as Florida (Steck et al., 2009) and the Carolinas in 2010 (Bur rack 2010).
Bait traps were crafted from clear 20-oz or 2-L soda bottles (modified from
Medeiros and Klaczko 1999). A curved slit was cut into the bottom portion of the
trap as an opening through which bait could be added. The slit was covered with
tape in spring and summer to inhibit wasps and bees from entering the trap.
Small holes were punctured into the bottle at random locations for fly entry. The
cap of the bottle was then removed and replaced with a standard shell vial that
was attached onto the top with tape. The bait was comprised of mashed rotten
banana, apple juice, and yeast. Traps were hung at two different locations on the
campus of Saint Joseph’s University in Philadelphia and Lower Merion, Penn -
Traps were maintained from July 2011 to December of 2011 and then again
from March to December 2012. Collections were performed multiple times per
week. Replacement traps were made at least once a week to ensure that emerg-
ing adults were not collected. Specimens were anesthetized with carbon dioxide,
sorted, sexed, classified, and placed in 95% ethanol for later study.
D. suzukii was identified using morphological characters (Vlach 2010) and
DNA sequencing. DNA was extracted (following a modified version of Gloor
and Engels, 1992) from a male specimen collected on 18 October 2011. A Nano
Drop spectrophotometer was used to estimate the DNA concentration (10.9
ng/μL). A vouch er sequence (Sample ID and GenBank accession number
GQ365213) of cytochrome oxidase subunit I (COI) was obtained from Barcode
of Life Data Systems v. 2.5 (Ratnasingham and Hebert 2007). Two sets of
primers were used for amplification with the polymerase chain reaction (PCR).
The first were universal primers obtained from Folmer et al. (2004):
72 ENTOMOLOGICAL NEWS
A second set of primers was designed to match the voucher sequence of
D. suzukii without mismatches:
COI was amplified using the DNA isolated from the D. suzukii male as tem-
plate (2 μL). The remaining components were: 1 μL (100 ng) of each primer (for-
ward and reverse). 11.4 μL of sterile deionized H2O, 4 μL of 5X buffer, 0.4 μL
of nucleotide mix, and 0.2 μL of Phusion High Fidelity Polymerase Enzyme
(New England Biolabs) for a total reaction volume of 20 μL. PCR protocol began
with an initialization step at 98°C for five minutes. The following steps were
repeated 35 times and included a denaturation step at 98°C for thirty seconds, an
annealing step at 50°C for thirty seconds, and an extension step at 72°C for forty-
five seconds. A final elongation step was then performed at 72°C for seven min-
utes. Amplifications were confirmed by gel electrophoresis using 1% agarose
stained with SYBR Safe DNA gel stain (Invitrogen).
The PCR product was amplified using the universal primers and purified with
the Qiagen PCR Clean-up kit. Sequencing was conducted using each of the uni-
versal primers by Genewiz, Inc. Sequences from both strands were aligned using
Geneious Pro (Drummond et al. 2011) software to the voucher sequence provid-
ed by Barcode of Life Databases v. 2.5 to determine the identity of the specimen.
RESULTS AND DISCUSSION
After performing both morphological and genetic identification of the speci-
men, it was concluded that the flies captured are D. suzukii. Allen L. Norrbom,
Systematic Entomology Laboratory, Agricultural Research Service, US Depart -
ment of Agriculture, confirmed the identification of both male and female Dro -
so phila suzukii specimens (Reference #1301082). Males are very distinctive
when compared to other specimens of the genus because of the dark wing spots.
Females, on the other hand, are not as easily detectable. The body coloration and
structure resembles that of both D. simulans and D. mela no gaster. The best
course to take when attempting to identify D. suzukii females in the presence of
other species in the Sophophora subgenus, is to use a dissecting microscope to
locate the large, saw-like ovipositor. Voucher specimens will be deposited at the
Academy of Natural Sciences in Philadelphia.
The genetic identification also confirms the taxonomy of the specimen. When
compared to the voucher sequence provided, the 619 base pair COI fragment
sequence obtained (GenBank JX272633) through extraction, amplification, and
sequencing is identical (100% identity). This sequence is also nearly identical to
those from Carvajal’s (2010) five sequences from flies from the San Diego, CA,
area, differing from their consensus at only one site. More specimens need to be
sequenced to determine how much variability exists in the natural population for
this portion of the COI gene.
Volume 123, Number 1, May and June 2013 73
In the 2011 collection season, 160 male and 44 female D. suzukii flies were
identified. In the 2012 collection season, the first D. suzukii fly captured was a
male in June. More D. suzukii flies were captured in 2012, perhaps because of
the mild winter of 2011-2012. Capturing D. suzukii in both 2011 and now in 2012
in the Philadelphia area implies that a breeding population is now established in
the area. This could have drastic implications for local fruit growers. Cini et al.
(2012) hypothesized that introduction and re-infestation in Europe is due to inter-
national/national trade and undetected infested fruits. This is probably also true
in the U.S.
It is unclear why the first D. suzukii flies were captured so late in 2011 com-
pared to those first caught in 2012. Perhaps this is when D. suzukii was intro-
duced to the area. The introduction could have been due to produce transporta-
tion or natural migration from the Carolinas to Pennsylvania. It would be valu-
able to focus future research on D. suzukii local adaptation and life-cycle as well
as the impact D. suzukii will have on local biodiversity.
We thank Dr. Denise Ratterman for assistance and supplies. The Systematic Entomology Labor -
atory of the USDA confirmed the species identification. Funds for this research were provided by the
Saint Joseph’s University Department of Biology and a Howard Hughes Medical Institute Student
Research Grant to P.F.
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