Pteromalus elevatus (Walker) (Hymenoptera: Pteromalidae): North American records of an immigrant parasitoid of the gall fly urophora jaceana (Diptera: Tephritidae)

6 Pages·1996·4.1 MB·

by  Hoebeke E Richard

PROC. ENTOMOL. SOC. WASH.
98(1), 1996, pp. 87-92
PTEROMALUS ELEVATUS (WALKER) (HYMENOPTERA: PTEROMALIDAE):
NORTH AMERICAN RECORDS OF AN IMMIGRANT PARASITOID OF THE
GALL FLY UROPHORA JACEANA (DIPTERA: TEPHRITIDAE)
E. RICHARD HOEBEKE AND A. G. WHEELER, JR.
(ERH) Department of Entomology, Cornell University, Ithaca, New York 14853-0901,
U.S.A.; (AGW) Bureau of Plant Industry, Pennsylvania Department of Agriculture, Har-
risburg, Pennsylvania 17110, U.S.A.
Abstract.(cid:8212)Pteromalus elevatus (Walker), a Palearctic species, is reported from several
localities in Nova Scotia as a probable parasitoid of the gall-inducing tephritid Urophora
jaceana (Hering) on black knapweed (Centaurea nigra). These records are only the third
for P. elevatus in the New World; the first such record (Newfoundland), published in the
European literature, has been overlooked by North American workers, and a collection
of specimens in New Brunswick has been briefly noted in the American literature. This
species is described and its distribution and habits in the Old World are summarized.
Key Words: Insecta, Pteromalidae, parasitism, adventive insects, biological control, Te-
phritidae
As part of continuing surveys for immi- (Burks 1979). In addition, Peschken et al.
grant insects in the Canadian Maritime (1982) reported that 3% of 580 U. cardui
Provinces, we report here the collection of (L.) larvae from galls on Canada thistle
Pteromalus elevatus (Walker) (Hymenop- (Cirsium arvense (L.) Scop.) at Sussex Cor-
tera: Pteromalidae), a species widely dis- ner, New Brunswick, were parasitized by
tributed in the western part of the Palearctic this pteromalid (as Habrocytus elevatus).
region and a known parasitoid of the knap- The two literature records and our own col-
weed gall fly Urophora jaceana (Hering) lection records for P. elevatus in Nova Sco-
tia are listed and mapped, together with a
(Diptera: Tephritidae). During the summers
short description of the parasitoid and in-
of 1993-1995, this pteromalid was taken at
formation on its geographic distribution,
numerous sites in Nova Scotia by sweeping
hosts, natural history, and possible mode of
flowerheads of black knapweed (Centaurea
introduction.
nigra L.). This plant is a principal host of
U. jaceana, also native to central and west- Pteromalus elevatus (Walker)
ern Europe and accidentally introduced into Eutelus elevatus Walker 1834: 366.
eastern Canada (Foote et al. 1993). Pteromalus elevatus: Walker 1848: 77,
Although a North American record Bouéek and Graham 1978a: 228, 1978b:
(Newfoundland) for P. elevatus was pub- 81.
lished by Graham (1969) in his monograph Habrocytus elevatus: Kurdjumov 1913: 13,
of the Pteromalidae .of Northwestern Eu- Bouéek 1965: 8, Graham 1969: 538.
rope, it was inadvertently omitted from the A complete synonymy for this species
list of pteromalids in the Catalog of Hy- can be found in Graham (1969: 538-539),
menoptera in America North of Mexico and Bouéek and Graham (1978a: 81).
88 PROCEEDINGS OF THE ENTOMOLOGICAL SOCIETY OF WASHINGTON
Fig. 1. Pteromalus elevatus, composite scanning electron photomicrograph. Propodeum, 65.
The large and diverse genus Pteromalus lum slightly less than width of head; prox-
Swederus (including Habrocytus Thomson, imal segments of funicle quadrate, the first
see Boucéek and Graham 1978a) contains usually at least very slightly shorter than
about 100 species in the western Palearctic pedicellus; scape reaching at most to level
region (Bouéek and Rasplus 1993), and an- of lower edge of median ocellus. Head
other 40 species in the Nearctic region hardly wider than mesonotum. Scutellum
(Burks 1979). Pteromalus elevatus is a discally finely to very finely reticulate.
member of the albipennis group, which in- Forewing with row of hairs on lower sur-
cludes about 30 Palearctic species (sensu face of costal cell complete; postmarginal
Graham 1969). vein of forewing as long as or slightly lon-
The female of P. elevatus, which is il- ger than marginal vein. Propodeum (Fig. 1)
lustrated by Varley (1947: 165) and Red- without a costula; panels of median area
fern (1983: Pl. 7, Fig. 2), can be readily quite strongly sculptured, for the most part
distinguished from those of native Nearctic very finely reticulate; median carina raised
species of the genus by the combination of to form a tooth subbasally. Gaster 1.1(cid:8212)1.6
its larger body size (2.5(cid:8212)5.5 mm), its host times as long as head plus thorax; at least
preferences (gall-forming tephritids in flow- 2.5 times as long as broad.
erheads of composites), and its unique pro- Distribution.(cid:8212)In the Palearctic region,
podeal structure (Fig. 1). P. elevatus is widely distributed throughout
Females (Fig. 2) (and males) of this ad- most of western Europe, including Great
ventive species are characterized as fol- Britain, Sweden, Czechoslovakia, and por-
lows: Head, thorax, and abdomen dark me- tions of the former Soviet Union (Molda-
tallic green; coxae and all, except apices of, via) (Graham 1969).
femora metallic green; tibiae and apices of In North America (Map 1), P. elevatus is
femora brown, tibiae centrally infuscate; currently known only from the following
tarsi yellowish, last segment dark brown. localities in New Brunswick (from a North
Anterior margin of clypeus at most mod- American literature record), Newfoundland
erately deeply emarginate. Antenna with (from a European literature record), and
combined length of pedicellus and flagel- Nova Scotia (from our own collecting):
VOLUME 98, NUMBER 1 89
Fig. 2. Pteromalus elevatus, composite scanning electron photomicrograph. Female habitus, lateral aspect,
35X.
New Brunswick: (cid:8220)(cid:8216)Sussex Corner, IV- ture records are deposited in the Canadian
1979, ex Urophora cardui galls on Canada National Collection of Insects (CNCI, Ot-
thistle shoots(cid:8217)? (see Peschken et al. 1982: tawa). All Nova Scotian specimens were
353). Newfoundland: (cid:8220)St. John(cid:8217)s, 12-V- collected or observed by the authors on
1958, R. E Morris, ex knapweed seed pod(cid:8221)(cid:8217) flowerheads of black knapweed (Centaurea
(see Graham 1969: 540). Nova Scotia: nigra); voucher specimens are deposited in
Cape Breton Co., Cape Breton Isl., Louis- the Cornell University Insect Collection
bourg, 24-VII-1995; North Sydney, 24-VII- (CUIC, Ithaca, NY) and the U.S. National
1995; Sydney, 23-VII-1995. Colchester Museum of Natural History (USNM, Wash-
Co., Truro, 22-VII-1995. Digby Co., Digby, ington, DC). |
20-VII-1994. Halifax Co., Halifax, 26-VI- Hosts and natural history.(cid:8212)In western
1993, 20-21-VII-1995. Inverness Co., Cape Europe, P. elevatus is a parasitoid of seed-
Breton Isl., Port Hawkesbury, 23-VII-1995. head tephritids on certain Asteraceae (=
Kings Co., Kentville, 21-VII-1994. Lunen- Compositae). Its natural history has been
burg Co., Lunenburg, 19-VII-1994, 21-VII- studied by Varley (1947) in Great Britain
1995. Shelburne Co., Shelburne, nr. marine (as Habrocytus trypetae Thomson), who re-
terminal, 19-VII-1994. Yarmouth Co., Yar- corded it as an ectoparasitoid of Urophora
mouth, 20-VII-1994. jaceana in galled florets of black knapweed
Specimens that served as the basis for the (cited as Centaurea nemoralis Jord.), and
Newfoundland and New Brunswick litera- by Redfern (1983), also in the British Isles,
90 PROCEEDINGS OF THE ENTOMOLOGICAL SOCIETY OF WASHINGTON
Map 1. Known distribution of Pteromalus elevatus in eastern North America. A, literature record from
Graham (1969: 540); B, literature record from Peschken et al. (1982: 353); all other records from authors(cid:8217)
collecting.
who recorded it as one of two common ec- is able to locate numerous gall fly larvae at
toparasitoids of U. stylata in galled shoots a stage suitable for parasitism. Newly
of bull (= spear) thistle (Cirsium vulgare emerged sexually immature females first
(Savi) Tenore). feed on the host without laying eggs. The
Eggs are laid in gall cells containing lar- Ovipositor is pushed down through the neck
vae and pupae of the gall fly, or in gall cells of the flask-shaped gall until it stabs a host,
already containing other parasitoids. Nu- which is stung and paralyzed. A secretion
merous eggs may be laid on a single host, hardens around the ovipositor to form a
but usually only one larva matures because tube through which the hemolymph of the
newly emerging larvae destroy any other host exudes; the female parasitoid then
eggs or larvae they encounter. The parasit- feeds on the hemolymph. Females generally
oid is not host specific and may attack lar- do not attack the nongall-forming tephritids
vae of the eurytomid Eurytoma curta Walk- in knapweed. Adults are found in the field
er and other parasitoids. Depending on cli- from May until August or occasionally Sep-
matic conditions, 2(cid:8212)3 generations are pro- tember.
duced annually. Pteromalus elevatus Pteromalus elevatus has also been re-
typically emerges in May and August, and corded as a parasitoid of the tephritid gall
VOLUME 98, NUMBER 1 91
flies Terellia serratulae (L.), Urophora car- in western North America (e.g. Harris and
dui (L.), U. stylata (FE), Noeeta pupillata Cranston 1979, Harris 1980). As a natural
(Fallén), and the tortricid moth Sparganoth- enemy of the unintentionally introduced U.
is pilleriana Schiffermiiller. This parasitoid jJaceana, P. elevatus poses little or no threat
has been reared from flowerheads of spe- to biological control of weed projects in
cies in the composite genera Centaurea, North America except for possible minor
Carduus, Cirsium, Arctium, and Hieracium. effects on U. cardui, a tephritid that has
Because of the difficulty in accurately iden- placed little stress on populations of Canada
tifying species of Pteromalus, some of thistle (Peschken et al. 1982).
these rearing records are probably doubtful
(Varley 1947, Peschken et al. 1982, Redfern ACKNOWLEDGMENTS
1983). We thank E. Eric Grissell (Systematic
Mode of introduction.(cid:8212)North American Entomology Laboratory, ARS, USDA,
populations of P. elevatus may have origi- Washington, DC) for confirming our iden-
nated from the accidental introduction of tification of Pteromalus elevatus and for
the gall fly U. jaceana, one of its principal critically reading and commenting on a
hosts, or with the intentional releases of U. draft of this paper, John Huber (Biological
cardui in eastern Canada. Larvae of U. ja- Resources Division, Agriculture Canada,
ceana live in the flowerheads of black Ottawa) for providing data for the known
knapweed (C. nigra), a species also intro- New Brunswick and Newfoundland speci-
duced from Europe and now widespread in mens of P. elevatus, and James K. Liebherr
the Maritime provinces, the Gaspé, Ontario, and Kip Will (Cornell University) for pro-
British Columbia, and the eastern United viding the scanning electron photomicro-
States. No doubt the gall fly was acciden- graphs in Figs. 1 and 2.
tally introduced with its host plant; it was
first collected in North America in 1923 at LITERATURE CITED
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