186 Florida Entomologist 86(2) June 2003 
THE GENUS RHOPALOSYRPHUS (DIPTERA: SYRPHIDAE) 
HOWARD V. WEEMS, JR.1, F. CHRISTIAN THOMPSON2, GRAHAM ROTHERAY3 AND MARK A. DEYRUP4 
'(retired) Florida State Collection of Arthropods, P.O. Box 2309, Hawthorne, FL 32640-2309 
'SystematicEntomology Laboratory, USDA, NHB-168 Smithsonian Institution, Washington, DC. 20560 
^Department of Natural History, Royal Museum of Scotland, Chambers Street, Edinburgh, EH1 1JF Scotland 
'Archbold Biological Station, P.O. Box 2057, Lake Placid, FL 33862 
ABSTRACT 
The flower fly genus Rhopalosyrphus Giglio-Tos (Diptera: Syrphidae) is revised. The genus 
is redescribed; a key to species is presented; the phylogenetic relationships of the genus and 
species are hypothesized; the included species are described; with new species, R. ramu- 
lorum Weems & Deyrup, described from Florida (type) and Mexico; R. australis Thompson 
from Brazil and Paraguay (type); and the critical characters are illustrated. 
Key Words: taxonomy, identification key, neotropics, nearctic 
RESUMEN 
El genero de la mosca de la flor del genero, Rhopalosyrphus, (DIPTERA: Syrphidae) es revi- 
sada y es redescrito; se presenta una clave para las especies; la relacion filogenetica del ge- 
nero y las especies es formulada; las especies incluidas son descritas; con las nuevas 
especies, R. ramulorum Weems & Deyrup, descrita de Florida (tipo) y Mexico; R. australis 
Thompson de Brasil y Paraguay (tipo); y los caracteres criticos son ilustrados. 
Translation provided by author. 
Rhopalosyrphus Giglio-Tos is a small group of 
microdontine flower flies restricted to the New 
World subtropics and tropics, ranging from south- 
ern United States to northern Argentina. These 
flies are rarely collected, only some two dozen 
specimens are known. The adults mimic eume- 
nine vespids, such as Zethus, which nest in twigs 
(Bohart & Stange 1965). The immature stages are 
known for only one species. These were found in 
ant nests (Pseudomyrmex) in twigs and grass 
culms, where the larvae probably prey on ant 
brood. The genus contains only three species. One 
wide ranging species, R. guentherii, is found from 
southwestern United States to northern Argen- 
tina. The others are more restricted in their 
ranges; R. ramulorum, presently known from a 
few specimens from Florida and Mexico, and R. 
australis from southeastern Brazil, Peru and Par- 
aguay. The genus is here revised, with complete 
synonymies, descriptions, and distributional and 
biological data given for all taxa. Adult terminol- 
ogy follows Thompson (1999), larval terminology 
follows Hartley (1961) and Rotheray (1991). 
GENUS RHOPALOSYRPHUS GIGLIO-TOS 
Rhopalosyrphus Gilgio-Tos 1891: 3. Type spe- 
cies, Holmbergia guentherii Lynch Arribalzaga 
(subsequent monotypy, Giglio-Tos 1892a: 2). Willis- 
ton 1892: 78 (catalog citation, descriptive note); 
Giglio-Tos 1892b: 34 [journal (1893:130] (descrip- 
tion); Aldrich 1905:347 (catalog citation); Kertesz 
1910: 360 (catalog citation); Hull 1949: 312, figs, 
(description, figures of habitus, head, abdomen, 
hind leg); Capelle 1956 (review, key); Cole & 
Schlinger 1969: 307 (descriptive notes); Thomp- 
son et al. 1976: 60 (catalog citation); Vockeroth & 
Thompson 1987: 729 (key reference). 
Holmbergia Lynch Arribalzaga 1891: 195. 
Type species, guentherii Lynch Arribalzaga 
(monotypy). Synonymy by Giglio-Tos (1892a). 
Head: face convex, produced anteroventrally, 
pilose; gena small, linear, pilose; frontal promi- 
nence absent, antenna inserted above middle of 
head; frons short, about yA as long as face, as wide 
as face (?) or slightly narrowed dorsally (8), pi- 
lose; vertex broad, about 3 times as long as frons, 
as wide as frons, not swollen, pilose and punctuate; 
ocellar triangle small, equilateral, well separated 
from eye margins; occiput broad on dorsal Vr, eye 
bare, dichoptic in male. Antenna elongate, longer 
than face; scape and basoflagellomere elongate, at 
least 4 times as long as pedicel; scape about 6 
times as long as broad; arista bare, inserted baso- 
laterally on mesal surface, about as long as scape. 
Thorax: longer than broad; postpronotum pi- 
lose; meso-anepisternum with anterior portion not 
differentiated, uniformly pilose; meso-katepister- 
num completely pilose; meso-anepimeron with 
posterior portion bare; meropleuron with barrette 
Weems et al.: Genus Rhopalosyrphus (Diptera: Syrphidae) 187 
pilose; metasternum developed, pilose (although 
reduced in some species); scutum punctuate, with 
appressed pile; metatibia expanded apically; 
scutellum with or without small apical calcar, 
without distinct ventral pile fringe. Wing: brown 
on anterior 1/3, extensively microtrichious; mar- 
ginal cell broadly open; stigmatic crossvein 
present; vein Ml with apical portion straight, 
joining vein R4+5 perpendicularly; vein M2 
present or absent; vein R4+5 with spur. 
Abdomen: petiolate; 1st segment short; 2nd 
segment as broad as thorax basally, but con- 
stricted, cylindrical apically; 3rd segment cylin- 
drical; 4th and 5th segments forming a compact 
club; aedeagus bifid. 
Puparium: elongate with broader ventral than 
dorsal surface; marginal band of variously-sized 
setae; dorsal surface flat; ventral surface convex; 
marginal band notched anteriorly; prothorax and 
mesothorax hidden beneath metathorax; mandi- 
ble with serrate ventral margin. 
Rhopalosyrphus belongs to the subfamily Micro- 
dontinae and is the sister group of Ceriomicrodon 
Hull, together these taxa are the sister group of 
Microdon Meigen, sensu lato. Rhopalosyrphus is 
defined (synapomorphy) by its 1) abdominal struc- 
ture and 2) pilose meropleuron. Other diagnostic 
characters are 3) antenna elongate, longer than 
face, usually about twice as long; 4) scape and ba- 
soflagellomere elongate; 5) face produced ven- 
trally; 6) occiput greatly developed on dorsal 1/3; 7) 
metasternum developed, not reduced; and 8) 
metatibia flared apically. The relationship to Micr- 
odon, sensu lato is unresolved: Rhopalosyrphus 
shares with the Microdon clade the bifid aedeagus 
and appears closely related to Ceriomicrodon. Ce- 
riomicrodon shares characters 3, 4, 5, 6, 7, 8 and 
its abdominal shape could be considered derived 
from that of Rhopalosyrphus. The two differ only 
by the presence of pile on the meropleuron. 
Microdon aurcinctus, described by Sack (1921: 
138) in Rhopalosyrphus, belongs to the Pseudomi- 
crodon group of Microdon. The species of this 
group differ from Rhopalosyrphus in the charac- 
ters listed above and in having the vertex swollen 
and shiny. 
Based on puparial characters, the immature 
stages of Rhopalosyrphus closely resemble Micro- 
don. They both have the anterior end consisting of 
the metathorax, with the prothorax and mesotho- 
rax hidden beneath it, a marginal band of setae 
which surrounds the puparium except for a notch 
at the anterior end, sharply-pointed antennomax- 
illary organs and mandibles with a serrated ven- 
tral margin. 
The very distinctive shape of the puparium of 
Rhopalosyrphus separates it from that of Micro- 
don: it has a curved ventral surface that is 
broader than the narrow, fiat dorsal surface. Also, 
the whole structure is elongate rather than oval 
in outline. The reverse appears in Microdon, with 
the dorsal surface being broader and curved and 
the ventral surface narrower and flat. These dif- 
ferences in shape suit the larva to life in hollow 
twigs and grass culms in which its prey, larvae 
and pupae of the ant, Pseudomyrmex, live. 
2. 
KEY TO SPECIES OF RHOPALOSYRPHUS 
3rd tergum short, about 1/3 as long as 2nd; 2nd tergum elongate (Fig. 9); eye with an area of enlarged ran- 
matidia medially and posterior to antenna australis 
3rd tergum elongate, as long as 2nd; 2nd tergum not greatly elongate posteriorly (Fig. 10); eye without en- 
larged ommatidia 2 
Alula completely microtrichose; cell R extensively microtrichose, bare only on basoposterior 1/4 or less; 
metasternum appearing bare, with pile greatly reduced; face and anepisternum partially black pilose 
ramulorum 
Alula bare basomedially; cell R completely bare behind spurious vein; metasternum with long, distinct pile, 
not reduced; face and anepisternum entirely white pilose guentherii 
Rhopalosyrphus guentherii Lynch Arribalzaga 
Figs. 10-13 
Holmbergia giintherii Lynch Arribalzaga 
1891: 198, Fig. 3 (habitus) Argentina, Buenos 
Aires (T 2 MACN lost?). Giglio-Tos 1892a: 2 
(notes), 1893: 131 [sep. 35], pi. 1, Figs. 10, lOa-b 
(description, figures of abdomen, wing); Aldrich 
1905: 347 (catalog citation); Kertesz 1910: 360 
(catalog citation); Fluke 1957: 36 (catalog cita- 
tion); Capelle 1956: 172, Fig. 2 (description, syn- 
onymy, key reference, figure of head); Thompson 
et al. 1976: 60 (catalog citation). 
Rhopalosyrphus carolae Capelle 1956: 174 A* 
6 2 Arizona, Huachuca Mts., Sunnyside Canyon 
(HT 2 UKaL). Byers et al. 1962: 168 (HT UKaL); 
Wirth et al. 1965: 599 (catalog citation); Cole & 
Schlinger 1969: 307 (descr. note, distr. western 
N.A.); Thompson et al. 1976:60. NEW SYNONYM 
Wing length: 8.8 mm (<J)-10.5 mm (9). Head: 
brownish black, yellowish white pilose; occiput 
grayish white pollinose on ventral 2/3, shiny dor- 
sally; eye with ommatidia of more or less equal 
size; antenna brownish black except orange basal 
1/3 of scape, about twice as long as face; antennal 
ratio 5: 1: 8. 
188 Florida Entomologist 86(2) June 2003 
Thorax: brownish black; pleuron silvery-white 
pilose; scutum brown pilose medially, silvery 
white pilose anteriorly, along transverse suture, 
laterally and posteriorly; scutellum silvery white 
pilose; calypter white, with brown margin and 
fringe; halter orange; wing brown anteriorly, hya- 
line posteriorly, microtrichose except bare cell R 
& BM, anterobasal 1/2 of cell CuP and basomedi- 
ally on alula; legs reddish brown except yellow 
basal 1/2 of metafemur; pro- and mesofemora 
black pilose anteriorly, yellow pilose posteriorly; 
pro- and mesotibia yellow pilose; tarsi black pi- 
lose; metafemur black pilose with a few yellow 
pili intermixed; metatibia yellow pilose has ally, 
black pilose apically. 
Abdomen: brownish black except yellow basal 
1/3 of 3rd tergum and reddish apically on 2nd ter- 
gum; 1st tergum white pilose; 2nd tergum con- 
stricted on apical 1/3, yellowish white pilose; 3rd 
tergum about twice as broad apically as has ally, 
yellow pilose; 4th tergum brown pilose basome- 
dial 2/3, yellow-white pilose apically, about as long 
as 2nd tergum; 5th tergum yellowish-white pilose. 
Distribution: Texas (Cameron, Harris, 
Hidalgo, Kenedy and Kleberg counties); Arizona; 
Mexico (Chiapas, Colima, Michoacan, Morelos); 
Guatemala, Costa Rica, Peru, Brazil, Paraguay, 
Argentina (Lynch Arribalzaga). 
Material examined: PARAGUAY: Colonia 
Nueva Italia, X-XI-1940, Pedro Willim (1 2 
AMNH). BRAZIL: Amazonas: Parana do Xiboren- 
inho, 03?15.S 60?00.W, mixed water, Canopy fog- 
ging project, TRS #60 Tray 392, 7-VIII-1979, 
Erwin, Adis & Montgomery (1 6 USNM ENT 
00032864 USNM). PERU: Lambayeque, 1 km S 
Lambayeque, 24, 26-27-VII-1975, C. Parker & L. 
Stange (1 2 USNM ENT 0003863 FSCA). COSTA 
RICA: Alajuela, Cerro La Lana, San Ramon, 1200 
m, LN 221750_481050, 17-1-1997, Betty Thomp- 
son, lot# 45327 (1 2 INBIOCRI002499628INBIO); 
Guanacaste, Estacion Exper. Enrique Jimenez 
Nunex, 20 km SW Canas, 5-17-XI-1991, Malaise 
Trap, A. S. Menke (1 2 USNM ENT 0003862 
USNM); Puntarenas, Goto Brus. Sabalis, Estacion 
El Progresso, Sector Fila Pizote, 1400 m, LS 
317700_597800, ll-V-2001, M. Alfaro Libre, lot* 
63200 (1 2 INB0003331118 INBIO). GUATE- 
MALA: Alta Vera Paz, Trece Aguas, "Cacao," XI- 
1905, "GPColl" (1 6 USNM). MEXICO: [label just 
as "Mex."], (1 S ANSP); Chiapas, Gutierrez, 20 
miles S Tuxtla, 12-VIII-1963, F. D. Parker & L. A. 
Stange (1 S USNM ENT 00032859 UCDavis); 
Colima, 6 km NE Tepames, 23-TX-Sept 1986, R. 
Miller & L. Stange (Id 19 USNM ENT 0003865- 
6 USNM, FSCA); Michoacan, Hidago, 12-VII-1963, 
F. D. Parker & L. A. Stange (1 9 USNM ENT 
00032858 UCDavis); Morelos, 3 miles N Alpuyeka, 
3400', 5-VI-1959, HE Evans (1 8 Cornell);..., Hua- 
jitlan, 27-K-1957, R. & K. Dreisbach (1 2 USNM 
ENT 00032867 FSCA); Puebla, Chinantla, Salle (1 
2 UTOR). USA. ARIZONA: [Cochise/Santa Cruz 
Counties], Huachuca Mts, Sunnyside Canyon, 9- 
VII-1940, DE Hardy (allotype 6, UKaL). TEXAS: 
Hidalgo Co: Pharr, 23-VI-1947 (1 2 USNM); La 
Joya, 19-111-1970, J, O'Grady (1 2 USNM), Rio 
Grande Park, 10 July 1981, A. Hook (1 ? 
USNM);... 12-VII-1981, A. Hook (1 2 USNM); 
McAllen, Valley Botanical Garden, 28-111-1975 (2 
S USNM ENT 0003868-9 FSCA),... 20-111-1976 (1 
2 USNM ENT 0003870 FSCA),... 3-IV-1975 (1 ? 
USNM ENT 0003871 FSCA),... 5-1V-1975 (1 2 
USNM ENT 003872 FSCA),... 2-LX-1975 (1 S 
USNM ENT 0003873 FSCA); Relampago, 17-X- 
1986, FC Fee (1 S 1 2 Fee) flying around flowering 
shrub, Schinus sp.; Santa Ana N.W.R., 17-X-1984 
(1 2 Fee); Madero, 18-X-1995, FD Fee (1 S Fee), 11- 
XI-1995, FD Fee (1 2 Fee) collected on flowers of 
composite shrub, Gochnatia hypoleuea DC. Kenedy 
Co.: 27?10.N 97?40.W, 8-X-1975, J.E. Gillaspy (1 6 
USNM). Cameron Co.: Brownsville, Los Palamos 
Mgt Area, 17X1976, FD Fee (1 2 USNM, 2 <J 
Fee); Brownsville, VI, ("Cata 1439" Brooklyn Mus 
Coll 1929 (1 2 USNM); Brownsville, 23-X-1976, 
FD Fee (1 3 2 2 Fee); Sabal Palm Grove Sanctuary, 
9X1986, FD Fee (1 2 Fee),... 20-X-1986, FD Fee 
(4 cj 1 2 Fee), all individuals fly about, attracted to, 
or feeding on exudate from glands at base of leaves 
of sapling trees of Ehretia anagua (Teran & Berl.) 
I. M. Johson;... 27-111-1988 (1 6 Fee), 5-IV-1988 (1 
<J Fee) flying about or attracted to flowers of Zan- 
thoxylum fagara (L.) Sarg.;... 21-XI-1995, FD Fee 
(1 6 Fee). Harris Co.: Houston, 45 W Virginia Str, 
28-VIII-1969, at black light trap, TJ Henry (1 $ 
USNM). Kleberg Co.: KingsviUe, South Pasture, 
26-TX-1976, at Baccharis, JE Gillaspy (1 6 USNM) 
The traditional nomenclature and taxonomy of 
Rhopalosyrphus are maintained. Giglio-Tos es- 
tablished that there was a single widespread spe- 
cies, ranging from Mexico to Argentina, and that 
the appropriate name for that taxon was Rhopal- 
osyrphus guentherii. The specimens studied sup- 
port the single widespread taxon concept of 
Giglio-Tos. That the appropriate name for the 
taxon is quentherii is not as certain, as the holo- 
type of quentherii has not been found and nothing 
mentioned in the original description will un- 
equivocally allow the assignment of that name to 
either the widespread taxon or australis. The 
types of Rhopalosyrphus carolae Capelle were ex- 
amined and are representative of the widespread 
taxon (new synonym). 
Rhopalosyrphus australis Thompson, new species 
Fig. 9 
Wing length: 10 mm (<?) - 11 mm (2). Head: 
Face reddish to brownish black (except holotype 
broadly yellowish dorsolateral), always black me- 
dially, white pilose except for a few black pili ven- 
trally; gena small, linear, white pilose; frons and 
vertex black, white pilose; occiput reddish brown, 
white pollinose and pilose on ventral 1/3, shiny 
Weems et al.: Genus Rhopalosyrphus (Diptera: Syrphidae) 189 
dorsally; eye with a medial fasciate area of en- 
larged ommatidia; antenna about 1.5 times as 
long as face, antennal ratio 5:1:10. 
Thorax: brownish black; pleuron white pilose; 
mesonotum punctate, very short appressed pi- 
lose, white pilose in males, more extensively black 
pilose medially in females; metasternum with 
short, appressed pile; calypter white, with brown 
margin and fringe; halter orange with brown 
head; wing brown anteriorly, hyaline posteriorly, 
microtrichose except bare cell R & BM, anter- 
obasal 1/2 of cell CuP and basomedially on alula; 
legs reddish brown except yellow basal 2/3 of 
metatibia, pale pilose except black pilose dorso- 
medially on pro- and mesotibiae and tarsi, with 
dense black spinose pile on ventrolateral 2/3 of 
metafemur, with ventromedial appressed black 
spinose pile on basal 2/3 of metatibia. 
Abdomen: black except yellow 3rd tergum and 
reddish apically on 2nd tergum, mainly short ap- 
pressed white pilose, except black pilose medially 
on 4th tergum; 1st short, as long as 3rd; 2nd ter- 
gum half as long as entire abdomen, constricted 
and cylindrical on apical 2/3, as wide as thorax 
basally; 3rd tergum short, as long as 1st; 4th ter- 
gum oval, as long as 2nd, forming with 3rd a dis- 
tinct club in <?; 5th tergum elongate, about 1/2 as 
long as 2nd, forming with 3rd and 4th a distinct 
club in 2. 
Distribution: Peru, southern Brazil and Para- 
guay. 
Holotype 2: PARAGUAY, Villarica, 1-1939, F. 
Schade, deposited in the American Museum of 
Natural History, New York. Paratypes: BRAZIL: 
Ceara, Russa, s., 11-1940, D. C. Alves (1 2 
USNM); Ceara, Limoeiro, X-1938, R. C. Shannon 
(1 6 USNM); Ceara, Luixeramobug, XI-1940, D. 
C. Alves (1 3 MZUSP); Minas Gerais, Belo Hori- 
zonte, 800 m, Estacao Ecologica, UFMG Campus, 
clear trail 60 m in from road, near swamp, Mal- 
aise trap, 8. D. Gaimari, 25-29-V-1993 (1 S 
USNM ENT 00032860 USNM),... 15-18-VI-1993 
(1 6 USNM ENT 00032860 USNM). PERU: Ju- 
nin, Colonia Perene, Rio Perene, 18 miles NE La 
Merced, 3-1-1955, E. I. Schlinger & E. S. Ross (1 2 
USNM ENT 00030699 CAS). 
Rhopalosyrphus austalis is readily distin- 
guished from the other two species of Rhopalosyr- 
phus by its distinctive abdominal shape. The 
epithet, australis, refers to the southern distribu- 
tion of the species and is an adjective. 
Rhopalosyrphus ramulorum Weems & Deyrup, 
new species 
Figs. 1-8, 14 
Wing length: 6 mm (S )-7 mm (?). Head: black; 
face silvery white pilose, with a few dark pili me- 
dially; frons sparsely white pilose, with a distinct 
bare fascia dorsally and separating off vertex; 
gena white pilose; vertex silvery white pilose, 
with a few dark pili medially; eye with ommatidia 
of more or less equal size; occiput white pilose on 
ventral 2/3, shiny dorsally; antenna brownish 
black except orange basal 1/3 of scape, about 1.5 
times as long as face; antennal ratio 5:1: 7 6 4:1: 
52. 
Thorax: black, silvery white appressed pilose 
on pleuron except with some dark pili on anepis- 
ternum; scutum dark appressed pilose except sil- 
very white pilose anteriorly, along transverse 
suture and anterior to scutellum; calypter white, 
with brown margin and fringe; halter yellow; legs 
dark brownish black, except yellow basal 1/3 of 
pro- and mesotibia and basal 2/3 of metatibia, 
black pilose except pale pilose on pale areas. 
Wing: extensively dark fumose, except paler on 
posterior 1/3, microtrichose except bare basal 1/3 
of cell R. 
Abdomen: black except very narrowly yellow 
basolaterally on 3rd tergum; 1st tergum black pi- 
lose laterally, white pilose medially; 2nd tergum 
constricted on apical 1/3, black pilose on basal 2/ 
3, white apically; 3rd tergum about twice as broad 
apically as basally, black pilose on basal 1/2, yel- 
lowish white pilose apically; 4th tergum about as 
long as 2nd tergum, black pilose on basal 1/2 and 
extending to posterior 1/3 laterally, yellowish 
white pilose on apicomedial 1/2 and apicolater- 
ally; 5th tergum yellowish white pilose. 
Puparium: 7.5 mm, width 2.5 mm; semi-circu- 
lar in cross-section with a ventral surface about 
twice as broad as dorsal surface; elongate, nearly 
3 times as long as broad; antennomaxillary or- 
gans (extracted from puparium) sharply pointed; 
prothorax and mesothorax retracted into met- 
athorax so that structures associated with 
mouthparts not visible; anterior margin of pupar- 
ium consisting of metathorax; cephalopharyngeal 
skeleton (extracted from puparium, Pig. 14) simi- 
lar to Microdon (Garnett et al. 1990); mandible 
blade-like, with serrated ventral margin, with 
rounded tip; abdominal segments with 5 dorsal 
(about marginal band of setae) groups of sensilla, 
each group with 2-3 terminal setae, 4 ventral 
groups which lack terminal setae, with some sen- 
silla group on two separate papillae; marginal 
band composed of 2 types of papillae alternating 
with each other: larger papillae with 3 terminal 
setae and smaller papillae with 2 terminal setae 
(Fig. 8); papillae comprising marginal band 
longer and packed close together on anterior and 
posterior ends of puparium; above these alternat- 
ing bands of papillae 2 rows of short papillae, 
about as long as those bearing sensilla; marginal 
band interrupted only on anterior margin of met- 
athorax; dorsal surface coated in small, dot-like 
papillae aggregated into vague reticulate pattern; 
ventral surface smooth, lacking setae and papil- 
lae; mid-dorsal region of abdominal segments 2-7 
with 6 longitudinal rows of larger papillae, be- 
tween outer 2 rows dot-like papillae densely ag- 
190 Florida Entomologist 86(2) June 2003 
""?-? "..  . ?:-;:f ?.>-.'.-5.-*Jfiw* 
'?  ? :?  ?"??  v^\fes?>SK*??? 
Figs. 1-8. Puparium of Rhopalosyrphus ramulorum. 1-3, habitus, 1, dorsal, 2, lateral, 3, anterior. 4, anterior spi- 
racular process, lateral. 5, 6, posterior respiratory process. 5, dorsal view and surrounding papillae, anterior end 
uppermost; 6, lateral view, anterior end to the left. 7-8. Papillae from marginal band. 
Weems et al.: Genus Rhopalosyrphus (Diptera: Syrphidae) 191 
Figs. 9-14. Features of Rhopalosyrphus. 9, abdomen, australis, dorsal; 10. Habitus guentherii, dorsal; 11, hind 
leg, guentherii, lateral; 12. head, guentherii, lateral; 13. abdomen, guentherii, lateral; 14. cephalopharyngeal skel- 
eton, ramulorum, lateral. Figures 10-13 from Hull (1949). 
gregated creating impression of vague pair of 
vittae running along dorsal surface (Fig. 1). Pos- 
terior respiratory process (Fig. 6): 0.3 mm long, 
0.2 mm high, oval, nodulate with mid-dorsal pro- 
jection, surrounded by papillae, with 4 pairs of in- 
terspiracular setae and 3 pairs of spiracular 
openings (Fig. 5). 
Distribution: USA (Florida) south to Mexico 
(Chiapas). 
Holotype S: USA: Florida, Highlands Co., 
Lake Placid, Archbold Biological Station, Trail 1 
SSo, 22-V-1985, Malaise Trap, M. Deyrup, depos- 
ited in the National Museum of Natural History 
(USNM), Washington. Paratypes: USA. FLOR- 
IDA, same locality as holotype, 5-V-1986, reared 
from nest of Pseudomyrmex simplex in twig of 
Carya floridana, M. Deyrup (1 9 USNM);..., L. L. 
Lampert, Jr. & H. W. Weems, Jr., 8-IV-1978 (2 6 
USNM ENT 0003891-2 FSCA);..., ll-IV-1978 (1 
5 USNM ENT 0003893 FSCA);..., 18-111-1975, 
H. W. Weems, Jr. (1 6 USNM ENT 0003894 
FSCA);..., 17-IX-1979, T. A. Webber & H. W. 
Weems, Jr. (1 9 USNM ENT 0003895 FSCA); F. 
E. Lohrer, H. W. Weems, Jr., 11-15-IV-1980 (1 9 
USNM ENT 0003896 FSCA),..., 21-22-IV-1980 (1 
6 USNM ENT 0003897 FSCA);..., 14-15-V-1980 
(1 6 USNM ENT 0003898 FSCA);..., 18-20-V- 
1980 (1 6 USNM ENT 0003899 FSCA); ..., High- 
lands Hammock State Park, 3-IV-1965, H. 
Weems, Jr. (1 9 USNM ENT 0003877 FSCA);..., 
27-111-1966 (1 9 USNM ENT 0003878 FSCA); 
Collier County, SR94, 1.8 miles south of US 41, 
25-11-1992, M. Deyrup & B. Ferster, reared from 
nest of Pseudomyrmex ejectus in culm of Cladium 
jamaicense (ABS); Liberty Co., Torreya State 
Park, 14-V-1964, H. Weems, Jr. (1 9 USNM ENT 
0003875 FSCA);..., 30-IV-5-V-1973, C. R. Artaud 
& H. Weems, Jr., Malaise trap, (1 S, 4 9 9 USNM 
ENT 0003879-83 FSCA, USNM); Alachua Co., 
Gainesville, Seville Heights, L. A. Stange, Black- 
light, 2-VII-1980 (2 9 9 USNM ENT 0003886-7 
FSCA);..., l-VII-1980 (1 9 USNM ENT 0003888 
FSCA);..., 5-VII-1980 (1 6 USNM ENT 0003889 
FSCA);..., 30-VII-1979 (1 9 USNM ENT 
0003890 FSCA); Dade Co., Ross & Castello Ham- 
mock, 30-111-1963, C. F. Zeiger (1 6 USNM ENT 
0003884 FSCA);..., Fuch's Hammock, near 
Homestead, 27-29-VII-1978, Terhune S. Dickel & 
H. Weems, Jr. (1 9 USNM ENT 0003885 FSCA); 
Chekika State Recreation Area, 10-XI-1982, FD 
Fee (1 8 Fee). MEXICO. Morelos, 3 miles N 
Alpuyeka, 3400', 5 June 1959, HE Evans, 14-V- 
192 Florida Entomologist 86(2) June 2003 
1959, Biol. Note 601 (1 6 USNM ENT 0003876 
FSCA); Chiapas, 28 miles west Cintalpa, 9-IV- 
1962, F. D. Parker (1 3 USNM). Another broken 
6 specimen is in the Canadian National Collec- 
tion and is labelled "Letitia, Colombia? (or Flor- 
ida)." According to Vockeroth (pers. comm.) this 
specimen was found in a Malaise trap which had 
been used both in the Florida Keys and Colombia. 
Rhopalosyrphus ramulorum is similar to guen- 
therii, but is smaller, narrower, not as robust, and 
has much more extensive black pile on face, 
scutum and anepisternum. The metasternal pile 
is greatly reduced and closely appressed, so the 
metasternum appears bare at low magnifications. 
Although many specimens of R. ramulorum 
have been collected, two of these are reared spec- 
imens and provide most of our insights into the 
natural history of the genus Rhopalosyrphus. 
When alive, the reared adults, like many other 
syrphids, bore a strong resemblance to stinging 
Hymenoptera. The wasp-like features of elongate 
antennae, narrow abdominal "petiole," pale bands 
and spots, and dark wings are enhanced by the 
wasp-like habit of holding the wings out from the 
body. The wings are also partially folded, so that 
they appear long and narrow. The general impres- 
sion is of a very small individual of the twig-nest- 
ing eumenid genus Zethus. 
One specimen was found in a nest of the ant 
Pseudomyrmex simplex in a small twig (hence the 
species epithet "ramulorum" the epithet to be 
treated as a noun in the genitive case) of Carya 
floridana in long unburned Florida scrub habitat. 
The adult emerged from its pupa the day after the 
twig was opened. A second specimen was in a nest 
of P. ejectus in a culm ofCladiumjamaicen.se; this 
adult also emerged a day after the nest was opened. 
The nests of these two species of Pseudomyrmex 
are kept clean and free of debris and fungi, and it 
is probable that the fly larvae are not scavengers, 
but predators feeding on ant brood. This would fit 
well with the known larval habits of the closely re- 
lated genus Microdon, (Duffleld 1981; Garnett et 
al. 1985). This is apparently the only known exam- 
ple of a predatory inquiline attacking members of 
the large neotropical ant genus Pseudomyrmex, 
though there must be others, especially among the 
Eucharitidae. Pseudomyrmex species are less sus- 
ceptible to inquilines than most ants because the 
nests are in plant cavities with access by only one 
or a few small, well-guarded holes, and the nests 
themselves are bare, with minimal edible detritus 
and no hiding places for inquilines. 
The holes used by Pseudomyrmex simplex and 
P. ejectus are much too small to permit the adult fly 
to escape, and it seems probable that emergence 
from the puparium is delayed until the nest has 
been broken open. Since the term "strategy" has 
been used extensively in discussing Microdon 
(Dufneld 1981), the problem of adult egress is a 
major flaw in the strategy of R. ramulorum. It may 
be, however, that there are ways an ovipositing fe- 
male can increase the likelihood that her offspring 
will be freed. Small, dead, exposed twigs are more 
likely to get broken off than larger twigs in the in- 
terior of the tree crown. Culms on the edge of a tus- 
sock of sedge or grass are more likely to get broken 
off than culms in the interior. If there is some spe- 
cial site selection by the female, this may explain 
why only two pupae were found in a 10-year study 
of Florida ants, a study that involved opening hun- 
dreds of colonies of Pseudomyrmex. 
This brings up the topic of apparent rarity of 
Rhopalosyrphus species, especially in Florida. At 
the Archbold Biological Station, two Townes traps 
running continuously for 3 years captured only 
one specimen. If the adults spend their time in 
the tops of trees or in extensive open marshes, 
this would explain why so few specimens appear 
in Malaise traps, which are usually set-up in un- 
derstory fryways. If R. ramulorum is actually de- 
pendent on chance events to release the adults, 
actual populations would need to be quite high for 
the sexes to meet, even if there were a mechanism 
for adult aggregation, and even if some synchro- 
nous emergence were provided by wind storms. 
Whatever the actual abundance of Rhopalosyr- 
phus species, the rarity of specimens in collec- 
tions suggests that there could be additional 
undiscovered species, especially in the neotropics, 
where the fauna of arboreal ants is large. 
ACKNOWLEDGMENTS 
This was a cooperative project: the larval taxonomy 
was done by Rotheray; nomenclature, literature review 
and adult taxonomy by Thompson; and biology by Dey- 
rup. After the manuscript was submitted for publication 
and during the review process, it was discovered that 
Weems was about to also describe the Florida species. 
Hence, Weems was added to this manuscript as a co-au- 
thor and his material was incorporated into it. We thank 
Drs. Paul Arnaud, Jr., California Academy of Sciences, 
San Francisco (CAS); George Byers, Snow Entomological 
Museum, University of Kansas (UKaL), Lawrence; Peter 
Cranston, University of California, Davis (UCD); Brian 
Pitkin, Entomology, The Natural History Museum (for- 
merly the British Museum (Natural History)), London 
(BMNH); Mauro Daccordi, Museuo Regionale di Storia 
Naturale, Torino (UTOR); John Gelhaus and Douglas 
Azuma, Academy of Natural Sciences, Philadelphia; 
David A. Grimaldi, the American Museum of Natural His- 
tory, New York (AMNH); Adriana Oliva, Museo Argentine 
de Ciencias Naturales Bernardino Rivadavia, Buenos 
Aires (MACN); Nelson Papavero, Museum of Zoology, 
Universidade de Sao Paulo, Sao Paulo (MZSP); J. R. Voc- 
keroth, the Canadian National Collection, Ottawa (CNC); 
Manuel Zumbado, Institute Nacional de Biodiversidad, 
Santo Domingo (INBIO), for permission to study material 
in their care. Suzanne Mangan assembled the plates, etc. 
We also thank Chris T. Maier, Connecticut Agricul- 
tural Experimental Station, New Haven; Neal Even- 
huis, B. Bishop Museum, Honolulu (BPBM); Frank D. 
Fee, State College (Fee); Gary Stock, Florida State Col- 
lection of Arthropods, Gainesville (FSCA); Nat Vander- 
Weems et al.: Genus Rhopalosyrphus (Diptera: Syrphidae) 193 
berg, James Pakaluk and Manya B. Stoetzel of the 
Systematic Entomology Laboratory, USDA, Washing- 
ton; and Marion Kotrba and Wayne N. Mathis of the 
Smithsonian Institution (USNM), Washington, for their 
critical review of the manuscript. 
REFERENCES CITED 
ALDRICH, J. M. 1905 A catalogue of North American 
Diptera. Smithsn. Misc. Coll. 46(2), 680 p. 
BOHART, R. M., AND L. A. STANCE. 1965. A revision of 
the genus Zethus Fabricius in the Western Hemi- 
sphere (Hymenoptera: Eumenidae). Univ. California 
Publ. Ent. 40, 208 p. 
BYERS, G. W., F. BLANK, W. J. HANSON, D. F. BENEWAY, 
AND R. W. FREDRICHSON. 1962. Catalogue of the 
types in the Snow Entomological Museum. Part III 
(Diptera). Univ. Kansas Sci. Bull. 43:131-181. 
CAPELLE, K. J. 1956. The genus Rhopalosyrphus, with a 
description of a new species from Arizona (Diptera, 
Syrphidae). J. Kansas Ent. Soc. 29: 170-175. 
COLE, F. R., AND E. I. SCHLINGER. 1969. The flies of 
Western North America, xii + 693 p. Berkeley & Los 
Angeles. 
DUFFIELD, R. M. 1981. Biology of Microdon fuscipennis 
(Diptera: Syrphidae) with interpretation of the repro- 
ductive strategies of Microdon species found north of 
Mexico. Proc. Ent. Soc. Washington 83: 716-724. 
FLUKE, C. L. 1957. Catalogue of the family Syrphidae in 
the Neotropical Region (Diptera). Revta Brasil. En- 
tomol. 7:1-181. [1957.06.20] 
GARNETT, W. B., R. D. AKRE, AND R. S. ZACK. 1990. Ex- 
ternal morphology of four species of Microdon imma- 
tures (Diptera: Syrphidae) from the Pacific 
Northwest. Ann. Ent. Soc. America 83: 68-80. 
GARNETT, W. B., R. D. AKRE, AND G. SEHLKE. 1985. Co- 
coon mimicry and predation by myrmecophilous 
Diptera (Diptera: Syrphidae). Florida Entomol. 68: 
615-621. 
GIGLIO-TOS, E. 1891. Diagnosi di quattro nuovi generi 
di Ditteri. Boll. Mus. Zool. Anat. Comp. Univ. Torino 
6 (108), 6 p. 
GlGLIO-TOS, E. 1892a. Sui due generi Sirfidi Rhopalo- 
syrphus ed Omegasyrphus. Boll. Mus. Zool. Anat. 
Comp. Univ. Torino 7 (118), 3 p. 
GlGLIO-TOS, E. 1892b. Ditteri del Messico. Parte I. Stra- 
tiomyidae?Syrphidae. 72 p., 1 pi. Also published in 
Mem. R. Accad. Sci. Torino 43 (Cl. Sci. Fis. Mat. 
Nat): 99-168,1 pi. 1893. 
HARTLEY, J. C. 1961. A taxonomic account of the larvae 
of some British Syrphidae. Proc. Zool. Soc. London 
136: 505-573. 
HULL, F. M. 1949. The morphology and inter-relation- 
ship of the genera of syrphid flies, recent and fossil. 
Trans. Zool. Soc. London 26: 257-408, 25 figs. 
KERTESZ, K. 1910. Catalogus dipterorum hucusque de- 
scriptorum. Vol. 7, 470 p. Lipsiae, Budapestini 
(^Leipzig, Budapest). 
LYNCH ARRIBALZAGA, F. 1891. Dipterologia Argentina 
(Syrphidae). An. Soc. Cien. Argentina 32: 80-99; 118- 
131; 194-202; 247-256; 307-314. 
ROTHERAY, G. E. 1991. Larval stages of 17 rare and 
poorly known British Hoverflies (Diptera: Syrphi- 
dae). J. Nat. Hist. 25: 945-969. 
SACK, P. 1921. Dr. L. Ziircher's Dipteren-Ausbeute aus 
Paraguay: Syrphiden. Archiv Naturgesch. (abt. A) 
87:127-149. 
THOMPSON, F. C. 1999. A key to the genera of the flower 
flies of the Neotropical Region with the description of 
two new genera and eight new species and a glossary 
of characters and terms used, Contr. American Ento- 
mol. Inst. 3: 321-378. 
THOMPSON, F. C, J. R. VOCKEROTH, AND Y. S. SEDMAN. 
1976. Family Syrphidae. Catalog. Dipt. Amer. S. 
United States 46,195 p. 
VOCKEROTH, J. R., AND F. C. THOMPSON. 1987. Family 
Syrphidae. Pp. 713-743. In J. F. McAlpine (ed.), Man- 
ual of Nearctic Diptera. Res. Br., Agric. Canada, 
Monogr. 28, v + pp. 675-1332. 
WILLISTON, S. W. 1892. Fam. Syrphidae. Pp. 57-79 (Feb- 
ruary 1892). In F. D. Godman and O. Salvin (eds.), 
Biologia Centrali-Americana, or, contributions to the 
knowledge of the fauna and flora of Mexico and Cen- 
tral America. Zoologia. Diptera. Vol. III. Taylor & 
Francis, London. 
WIRTH, W. W., Y. S. SEDMAN, AND H. V. WEEMS, JR 
1965. Family Syrphidae. Pp. 557-625. In A. Stone, 
C. W. Sabrosky, W. W. Wirth, R. H. Foote and J. R. Coul- 
son (eds.), A catalog of the Diptera of America north of 
Mexico. U. S. Dept. Agric. Handbk 276,1696 p.