Content uploaded by P. J. Johnson
Author content
All content in this area was uploaded by P. J. Johnson on Jan 27, 2016
Content may be subject to copyright.
Proceedings of the South Dakota Academy of Science, Vol. 94 (2015) 297
MORPHOLOGICAL AND ECOLOGICAL
DISCRIMINATION OF TWO STENODIPLOSIS
(DIPTERA: CECIDOMYIIDAE) ON
ALOPECURUS ARUNDINACEUS, A. PRATENSIS
AND BROMUS INERMIS (POALES: POACEAE)
IN EASTERN SOUTH DAKOTA
J. Manuel Perilla López, Paul J. Johnson*, and Arvid Boe
Insect Biodiversity Lab., Dept. of Plant Science,
Box 2207A, South Dakota State University,
Brookings, SD 57007
*Corresponding author email: paul.johnson@sdstate.edu
ABSTRACT
Two of four species of Stenodiplosis (Diptera: Cecidomyiidae) known in eastern
South Dakota are non-native introductions occurring on introduced grasses:
Stenodiplosis bromicola is associated with Bromus inermis and S. geniculati as-
sociated with Alopecurus arundinaceus and A. pratensis. Stenodiplosis bromicola
is newly reported from South Dakota. Inorescences of the host grasses were
observed, and gall midges and parasitoids were found ovipositing. Morphological
dierences between the gall midges were found in the circumla, distribution of
posterior setae on tergites, width to length ratio of female cerci, and gonostylus
shape in males. A key is presented to separate these species from each other and
the two native species, S. spartinae and S. wattsi. Both introduced Stenodiplosis
species are parasitized by species of Eulophidae (Hymenoptera). Stenodiplosis
bromicola and S. geniculati both host an apparently undescribed Aprostocetus sp.
1. Aprostocetus, a Quadrastichus sp., and Tetrastichus bromi were found parasit-
izing only S. bromicola, Aprostocetus sp. 3 and an undetermined Aphelinidae
hyperparasitoid emerged from S. geniculati. Evaluation of morphological and
ecological traits supports the recognition of two sympatric species in space and
time, with a mostly similar parasitoid guild diering by one species.
INTRODUCTION
Gall midge species of the genus Stenodiplosis Reuter are dened in part by
their larval feeding habits on ovules and developing caryopses of grasses. Gagné
and Jaschhof (2014) listed 6 species in the genus for North America, three be-
ing native to North America (S. albescentis Gagné, S. phragmicola Sinclair and
Ahee, S. wattsi Gagné), and additional undescribed species known, and another
three introduced to North America (S. bromicola Marikovskij and Agafonova, S.
geniculati Reuter, S. sorghicola Coquillett). e two species of interest here are in
this second group of introduced species, S. bromicola and S. geniculati.
298 Proceedings of the South Dakota Academy of Science, Vol. 94 (2015)
Stenodiplosis species are separated most reliably from those in Contarinia Ron-
dani, by the lack of lateral setae on the adult abdominal tergites, reduced size
of larval papillae, and lack of a larval instar spatula (Gagné 1994). Stenodiplosis
bromicola and S. geniculati were recently discovered in South Dakota and were
found to be dicult to separate without their previously associated host plants.
Stenodiplosis bromicola is associated with Bromus inermis Leyss. (smooth brome-
grass) and S. geniculati is associated with Alopecurus arundinaceus Poir. and A.
pratensis L. (foxtail grasses). e published descriptions of S. bromicola and S.
geniculati do not provide direct comparisons of these species and there is no
morphology-based review of the species of Stenodiplosis, thus making adult dif-
ferentiation dicult.
Few ecological details are known of these gall midges other than recorded
host plants (Reuter 1895, Barnes 1946) and larval feeding. Most available in-
formation is for S. bromicola on B. inermis in agronomic circumstances (e.g.,
Agafonova 1962; Neiman and Manglitz 1972). e feeding on grass ovules and
developing caryopses is apparently a generalized habit for all Stenodiplosis spe-
cies (Coquillett 1899; Agafonova 1962; Neiman and Manglitz 1972; Boe 1991;
Ahee et al. 2013). Summer-developing larvae overwinter and pupate in orets on
the plant or in soil (Neiman and Manglitz 1972; Gagné 1989). Parasitoid wasps
of the genus Aprostocetus Westwood (Hymenoptera: Eulophidae) were reared
from several Stenodiplosis species (Coquillett 1899 [as “Apostrocetrus”]; Boe and
McDaniel 1990; Johnson et al. 2015). Although Agafonova (1962), Neiman and
Manglitz (1972), Vogel and Manglitz (1989) and others reported a “Tetrastichus
sp.” as a parasitoid of S. bromicola and S. wattsi, we believe those refer to one or
more Aprostocetus spp. (Z. Yefremova, in litt.).
Our goal in this report is to provide a morphology-based key for dierentia-
tion of the introduced S. bromicola and S. geniculati from two native regional
species, and provide additional ecological observations on phenology and parasit-
oids. is information is combined with host associations to further demonstrate
species segregation and provide recognition of two species as taxonomic and
ecological entities in our local populations.
METHODS
Adults were reared or collected by aspirator from inorescences of Alopecurus
arundinaceus, A. pratensis and Bromus inermis during the growing season of 2014
and May-Jun of 2015. Samples were taken at twelve sites in Brookings County,
South Dakota. Larvae were dissected from orets where adult females perched
and oviposition was observed, or larvae were reared using the methodology
described by Perilla López et al. (2015). Gall midge and parasitoid specimens
were stored in 100% alcohol. Eight males and females of each species were slide
mounted for morphological analysis, generally following the method in Gagné
(1989), except that potassium hydroxide was used as a clearing reagent instead of
sodium hydroxide. Identications were made using published literature and con-
rmed by R.J. Gagné, USDA-ARS-SEL, Washington, D.C. Specimen vouchers
were deposited in the Severin-McDaniel Insect Research Collection (SDSUC),
Proceedings of the South Dakota Academy of Science, Vol. 94 (2015) 299
South Dakota State University Brookings, South Dakota. Plant names used are
from Barkworth et al. (2007).
RESULTS
A Key to the Adult Stenodiplosis of Eastern South Dakota
1. Sternites 2-7 with trichoid sensilla absent ............................................... 2
1’. Sternites 2-7 with trichoid sensilla present.............................................. 3
2. Palpus 1-2 segmented; Aedeagus as long as hypoproct or slightly longer;
associated with Spartina pectinata .............................. S. spartinae Gagné
2’. Palpus 4 segmented; aedeagus clearly longer than hypoproct; associated
with Andropogon girardii, A. hallii, Schizochyrium scoparium and Sorghastrum
nutans ..............................................................................S. wattsi Gagné
3. Female agellomeres with circumla as irregular threads and sinuous
(Figure 1a); cerci 2.2-2.7 times longer than wide, gradually tapered with
1 long seta near base, 2-4 setae gathered on the last third of it, and several
setae with similar size along length (Figure 1c). Males with gonostylus in
lateral view gradually tapering from broad base to narrowed apex with
distal part approximately half of the width of the base; rst through
seventh tergites with latero-posterior 5 to 14 setae, having more (close to
11) in the third to fth tergites, in two medially discontinuous rows that
are not equally separated, with few setae in one irregular row; tergites,
second through seventh sternites and the area surrounding each seta
lightly pigmented; associated with Bromus inermis and B. riparius ............
.............................................. S. bromicola Marikovskij and Agafonova
3’. Female agellomeres with looped circumla (Figure 1b); cerci 3.3-4.0
times longer than wide, base narrower than S. bromicola with 1 long seta
near base, several shorter setae gathered toward the distant half (Figure 1d).
Males with gonostylus in lateral view wide and of nearly equal width
throughout; rst through seventh tergites with 3 to 7 posterior setae,
sometimes having fewer on the third to fth tergites, mainly in one row
medially discontinuous equally distant between them. Tergites, second
through seventh sternites and the area surrounding each seta is as
pigmented as the thoracic areas; associated with Alopecurus arundinaceus,
A. geniculati, A. pratensis ........................................... S. geniculati Reuter
Phenology—In 2014 the emergence of the rst spring generation of adults of
both species of gall midges coincided with the appearance of A. arundinaceus and
B. inermis inorescences during the rst week of June. However A. arundinaceus
inorescences started their emergence in late May. Due to a delayed growing sea-
son, the rst inorescences were also available on the second week of June, caus-
ing simultaneous availability of A. arundinaceus and B. inermis inorescences.
300 Proceedings of the South Dakota Academy of Science, Vol. 94 (2015)
e S. bromicola adult emergence and activity period was extended by two weeks
(3-18 July) due to the longer developmental time of B. inermis inorescences.
In 2015, adults of S. geniculati were active as soon the A. arundinaceus and A.
pratensis inorescences began exertion from the leaf sheath during the rst week
of May. Females were observed laying eggs in inorescences when at least 20%
of the inorescence became exerted and through the pre-anthesis period. Bromus
inermis inorescences developed later, with the rst oviposition by S. bromicola
recorded on May 26. In both years, inorescences of B. japonicus and B. tectorum
were taken to the laboratory, however no midges emerged from these two annual
bromes. e lack of gall midge association with annual bromes was also reported
by Neiman and Manglitz (1972).
Eggs of both species were laid in unfertilized owers before the stamens were
exerted from the oret. For S. geniculati, only one egg was found in most of the
orets dissected, with only 1% of infested orets having two larvae. In this lat-
ter case it appeared that internecine competition may prevent at least one larva
reaching full development.
In eastern South Dakota, generational life cycles for S. bromicola and S. genicu-
lati were similar in duration from 10 to 15 days, and similar to that described by
Agafonova (1962) for S. bromicola in the Kursk Province of Russia. No evident
symptoms or malformations were observed in the tissues of infested orets. is
same observation was made on inorescences of Andropogon gerardii, Schizachy-
rium scoparium and Sorgahstrum nutans with larvae of S. wattsi, and larvae of
Stenodiplosis spartinae on Spartina pectinata.
Contemporaneous with and following adult activity of S. bromicola and S. ge-
niculati, adults of Aprostocetus wasps were observed walking on the inorescence
and ovipositing in the orets of A. arundinaceus and B. inermis. Examination of
Stenodiplosis larvae in situ revealed the presence of ectoparasitoid larvae. Adult
Aprostocetus were reared from all gall midge infested inorescences of both A.
arundinaceus and B. inermis
Parasitoids--Totals of 823 S. geniculati and 689 parasitoids were reared from
A. arundinaceus, and 129 S. bromicola and 315 parasitoids from B. inermis dur-
ing the 2014 growing season. e sex ratios for both species were similar: 43-
44% male and 56-57% female.
Tetrastichis bromi Kostyukov was found as the dominant species of parasitoid
in S. bromicola. Originally from Ukraine and Russia, T. bromi was probably in-
troduced to North America during the late 19th century in imported B. inermis
seed infested with S. bromicola (Newell and Keim 1943; Newell 1973; Dunn
1985). is wasp was only recently recognized as part of our fauna, appar-
ently previously confounded with A. nebraskensis (Girault). Tetrastichis bromi
was reared from S. bromicola at an infestation at a rate of 29.5% throughout the
emergence period in 2014. is is a low infestation rate compared to the pro-
portions given by Agafonova (1962) who found that parasitism rates increased
through each sequential gall midge generation.
ree additional eulophid parasitoid species were also reared from S. bromi-
cola, two apparently undescribed Aprostocetus species designated morphospecies
1 and 2, and a Quadrasticus sp. Aprostocetus sp. 1 occurred at a 38% infestation
Proceedings of the South Dakota Academy of Science, Vol. 94 (2015) 301
rate, and was also reared from S. geniculati. is is the only parasitoid reared
from both species. At this time it is not is clear if this wasp is native or intro-
duced. e total parasitism rate for S. bromicola was 71%. is occurrence of
multiple species of parasitoids suggests inter-specic competition among S. bro-
micola parasitoids and could be a reason for dierences between this rate and the
T. bromi parasitism rates observed by Agafonova (1962).
e parasitism rate for S. geniculati by Aprostocetus sp. 1 was 44.8%. is
was the most prevalent parasitoid and is shared with S. bromicola. A third ap-
parently undescribed Aprostocetus species is Aprostocetus sp. 3. Additionally an
undetermined species of Diapriidae (Hymenoptera) was reared once from this
gall midge. e total parasitism rate for S. geniculati was 45.6%. During 2015,
an undetermined species of Aphelinidae was reared from A. arundinaceus samples
with S. geniculati.
Seed Production—e damage by these gall midges to grass seed production
varies considerably from very low and undetectable to 100% infestation rates on
B. inermis by S. bromicola (Agafonova 1962; Neiman and Manglitz 1972), and
from 20-80% in A. arundinaceus by S. geniculati. ese rates are signicant for
seed production and impact the commercial production of these grasses used
as forage crops (Barnes 1946). Whether seed loss from gall midge predation
impacts the biological control of unwanted B. inermis remains for evaluation.
SUMMARY
Previously unrecognized morphological dierences were found in gonostylus
shape, female circumla and width-length proportions in the female cerci, dis-
tinguishing S. bromicola and S. geniculati. Phenologically, the two species have
similar life cycles, seasonality, and they commonly co-occur in anthropogenic
habitats, including their introduced host plants. e parasitoid T. bromi seems
restricted to S. bromicola, with apparently undescribed species of Aprostocetus
recovered from both gall midges species S. bromicola and S. geniculati. Steno-
diplosis bromicola is host specic to B. inermis, and S. geniculati is restricted to
at least two species of Alopecurus, i.e. A. arundinaceus and A. pratensis. e data
analyzed and interpretations support the species distinction of S. bromicola and
S. geniculati.
ACKNOWLEDGMENTS
We thank Raymond J. Gagné, USDA-ARS-SEL (retired) for technical assis-
tance with gall midge systematics and review of the manuscript; Zoya Yefremova,
Tel Aviv University, for Aprostocetus determinations and advice; Gary E. Larson,
SDSU Professor and Curator of the C.A. Taylor Herbarium (retired) for review
of the manuscript; and the North-Central Sun Grant Initiative through USDA-
NIFA award number 2010-38502-2186.
302 Proceedings of the South Dakota Academy of Science, Vol. 94 (2015)
LITERATURE CITED
Agafonova, Z.Y. 1962. Development of the midge Stenodiplosis bromicola Mar. et
Ag. (Diptera: Itonididae), in relation to peculiarities of brome biology (Bro-
mus inermis Leyss. and riparius Rehm.). Entomological Review 41:11-21.
Ahee, J.E., B.J. Sinclair, and M.E. Dorken. 2013. A new species of Stenodiplosis
(Diptera: Cecidomyiidae) on orets of the invasive common reed (Phrag-
mites australis) and its eects on seed production. e Canadian Entomolo-
gist 145:235-246.
Barkworth, M.E., L.K. Anderton, K.M. Capels, S. Long, and M.B. Piep. 2007.
Manual of Grasses for North America. Utah State University Press, Logan,
UT.
Barnes, H.F. 1946. Gall midges of economic importance. Vol. II: Gall midges of
Fodder Crops. Crosby Lockwood & Son LTD, London.
Boe, A. 1991. A new host record for Contarinia geniculati (Reuter) (Diptera:
Cecidomyiidae). Proceedings of the Entomological Society of Washington
93(3):789.
Boe, A., and B. McDaniel 1990. Conioscinella nuda (Adams) and Tetrastichus
nebraskensis (Girault) reared from big bluestem inorescences in South Da-
kota. Prairie Naturalist 22:207-210.
Coquillett, D.W. 1899. A cecidomyiid injurious to seeds of sorghum. U.S. De-
partment of Agriculture, Division of Entomology, Bulletin 18:81-82.
Dunn, P.H. 1985. Origins of leafy spurge in North America. Pages 7-13 in
A.K.Watson, editor. Leafy Spurge, Monograph series of the Weed Science
Society of America No. 3.
Gagné, R.J. 1989. e Plant-Feeding Gall Midges of North America. Cornell
University Press, Ithaca and London.
Gagné, R.J. 1994. e gall midges of the Neotropical region. Cornell University
Press, Ithaca and London.
Gagné, R.J., and M. Jaschhof. 2014. A Catalog of the Cecidomyiidae (Diptera)
of the World, 3rd Edition. Digital version 2. Available at: http://www.
ars.usda.gov/SP2UserFiles/Place/80420580/Gagne_2014_World_Cecido-
myiidae_Catalog_3rd_Edition.pdf [last accessed 02 July 2015]
Perilla López, J.M., P.J. Johnson, R.J. Gagné, and A. Boe. 2015. A new species of
Stenodiplosis (Diptera: Cecidomyiidae) on Spartina pectinata (Poaceae) with
notes on its biology and parasitism by Tetrastichus bromi (Hymenoptera:
Eulophidae). Zootaxa. In press.
Neiman, E.L., and G.R. Manglitz. 1972. e biology and ecology of the brome-
grass seed midge in Nebraska. Nebraska Agricultural Experiment Station
Research Bulletin 252.
Newell, L.C. 1973. Smooth Bromegrass, Pages 254-262 in M.E. Heath, D.S.
Metcalfe, and R.F. Barnes, R.F. editors. Forages: e Science of Grassland
Agriculture, 3rd. edition. Iowa State University Press, Ames, IA.
Newell, L.C., and F.D. Keim. 1943. Field performance of bromegrass strains
from dierent regional seed sources. Journal of the American Society of
Agronomy 35:420-434.
Proceedings of the South Dakota Academy of Science, Vol. 94 (2015) 303
Reuter, E. 1895. Zwei neue Cecidomynen. Acta Societatis pro Fauna et Flora
Fennica 11: 1-18.
Vogel, K.P., and G.R. Manglitz. 1989. Bluestem seed midge inuence on sexual
reproduction of big bluestem: a review. Pages 267-270 in T.B. Bragg and J.
Stubbendieck, editors. Prairie Pioneers: Ecology, History and Culture: Pro-
ceedings of the Eleventh North American Prairie Conference, August 7-11,
Lincoln, Nebraska. University of Nebraska Printing, Lincoln, NE.
Figure 1. a. Stenodiplosis bromicola, first female flagellomere (anterior). b.
Stenodiplosis geniculati, first female flagellomere (anterior).c. Stenodiplosis bromicola,
female cerci (dorsal). d.Stenodiplosis geniculati, female cerci (dorsal). Scale bar = 0.02
mm.
c
a
d
b
Figure 1. a. Stenodiplosis bromicola, first female flagellomere (anterior). b. Stenodiplosis ge-
niculati, first female flagellomere (anterior). c. Stenodiplosis bromicola, female cerci (dorsal). d.
Stenodiplosis geniculati, female cerci (dorsal). Scale bar = 0.02 mm.
