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100(4), 1998, pp. 658-664 



(NEW) Systematic Entomology Laboratory, PSI, Agricultural Research Service, U.S. 
Department of Agriculture, % National Museum of Natural History, MRC-168, Washing- 
ton, DC 20560, U.S.A. (e-mail: nwoodley; (DDJ) Department of En- 
tomology, Smithsonian Institution, MRC-169, Washington, DC 20560, U.S.A. 

Abstract.—The egg and puparium of Stylogaster biannulata (Say) (Diptera: Conopidae) 
are described and illustrated in detail based on examination by scanning electron micros- 
copy. This species was reared from Gryllus rubens Scudder in Florida, a new host record. 
Previous literature is reviewed in light of this new data. 

Key Words: 

The genus Stylogaster Macquart has 
about 85 species distributed primarily in 
tropical regions in both hemispheres (Smith 
1979: fig. 1). The greatest diversity is in the 
New World where 63 species occur (Cam- 
ras and Parrillo 1985), two of which are 
found in the Nearctic Region. This paper 
reports new data on hosts and immature 
stages for Stylogaster biannulata (Say) 
which occurs from Rhode Island to Ne- 
braska, south to Texas, Florida, and Vera- 
cruz, Hidalgo, and San Luis Potosi in Mex- 
ico (Camras 1965, Camras and Parrillo 
1985). The other Nearctic species, S. neg- 
lecta Williston, is known from Massachu- 
setts to Nebraska, south to Arizona, Geor- 
gia, and Sinaloa and Chiapas in Mexico; its 
biology remains completely unknown. 


The enigmatic biology of Stylogaster has 
been the subject of much speculation ever 
since Bates (1863: 365) published one of 
the first naural history observations of Styl- 
ogaster females hovering over advancing 
swarm raids of army ants of the genus Eci- 
ton Latreille. Early authors [see Aldrich 

Stylogaster biannulata, Conopidae, hosts, egg. puparium, Gryllus rubens 

(1930) for a good summary] were of the 
opinion that Snlogaster must have been us- 
ing army ants as hosts. Lopes (1937) found 
eggs of Stylogaster on an unspecified or- 
thopteran and a cockroach. Later observa- 
tions, particularly detailed ones by Retten- 
meyer (1961), showed that the conopids 
were ovipositing on insects displaced by the 
advancing ants, as well as other insects, es- 
pecially tachinid flies of the genera Calod- 
exia Wulp and Androeuryops Beneway 
looking for hosts displaced by the ants. 
However, Rettenmeyer was of the opinion 
that cockroaches and possibly other orthop- 
teroid insects were the most likely hosts of 
Stylogaster, and eggs were inserted acci- 
dentally into tachinids utilizing the same 
hosts. He did, however, note (1961: 1015) 
that one of 17 Stylogaster eggs found on 
tachinids had initiated development, so he 
did not completely discount tachinids as 
hosts. Stuckenberg (1963), Smith (1967, 
1969), and Smith and van Someren (1985) 
discussed the occurrence of Stylogaster 
eggs on various calyptrate Diptera, primar- 
ily Muscidae, in the Afrotropical Region. 
Some of these flies were associated with 


driver ants while others were associated 
with animal dung (and in the fatter case 
Stylogaster eggs were found on flies outside 
of the geographic distribution of driver 
ants). Stuckenberg (1963) was of the opin- 
ion that because Stylogaster eggs were 
more common on dung-breeding muscids 
he studied than was observed by Retten- 
meyer (1961) in Panama, it was more likely 
that flies were the true Stylogaster hosts in 
Africa. Smith (1979) noted that Stylogaster 
ligepae Smith was collected while hovering 
over a bird nest, and speculated that per- 
haps they were looking for flies attracted to 
dung or carrion in or near the nest. 

All of the above evidence concerning 
Stylogaster hosts is circumstantial. It was 
not until Smith and van Someren (1985) re- 
ported dissecting larvae of Stylogaster var- 
ifrons Malloch from cockroach nymphs and 
a larva of S. westwoodi Smith from a gryl- 
lid cricket that unequivocal host associa- 
tions were known. Adults of both species 
were seen Ovipositing on their hosts being 
displaced by army ants in a garden in Ke- 

One of us (NEW) was sent a collection 
of Diptera reared from Gryllus spp. by Tho- 
mas J. Walker and his associates near 
Gainesville, Alachua County, Florida. 
While most of the specimens were Tachin- 
idae of the genera Ormia Robineau-Des- 
voidy and Anisia Wulp, it was surprising to 
find some specimens of Stylogaster bian- 
nulata in the lot. Most of the Stylogaster 
specimens had been reared from Gryllus 
rubens Scudder with a couple being reared 
from unidentified Gryllus. Susan Wineriter 
(personal communication) provided some 
details about how these collections were 
made. The crickets were collected mostly 
in sound traps (Walker 1986) with some 
taken in pitfall traps. Crickets were held 
alive in the lab individually to check for 
parasites for up to 9 d, the main aim being 
to study the parasitism level in the crickets 
by Ormia ochracea (Bigot). It was estimat- 
ed that about 1000 crickets were censused, 
and from these only 25-30 puparia of Styl- 


ogaster biannulata were obtained. Puparia 
were obtained from crickets collected in 
May, August, September, October, Novem- 
ber, and December. Although not observed, 
the larvae probably emerged from their 
cricket hosts because puparia were found 
outside the host. In a few cases more than 
one S. biannulata puparium came from a 
single cricket, and in at least one case S. 
biannulata and the tachinid Anisia gilvipes 
(Coquillett) successfully parasitized a single 
cricket. In the three cases where data were 
recorded, the S. biannulata adults emerged 
19-25 days after their puparia were formed. 
Nothing is known about how Stylogaster 
biannulata locates its host. It certainly is 
not dependent on above-ground army ants 
as they do not occur in the United States. 


The eggs of Stylogaster were first de- 
scribed by Lopes (1937). Subsequently it 
was discovered that the eggs have species- 
specific characters which have been illus- 
trated for many species (Lopes 1938, Lopes 
and Monteiro 1959, Monteiro 1960, Smith 
1967, 1979). The end opposite the micro- 
pyle is pointed and has subapical] barbs, and 
this end is embedded in the insect victim at 
the time of oviposition. The actual mecha- 
nism of oviposition is unknown (Kotrba 
1997, reviews the data on this subject). 

We obtained about a dozen eggs from a 
female of Stylogaster biannulata that was 
collected at Lick Creek Park, Brazos Coun- 
ty, Texas. A figure (Smith and Peterson 
1987: fig. 54.25) of the egg of this species 
has been published but no further descrip- 
tive details were given. Because the egg has 
not been described in detail, we present in- 
formation on its morphology, based on 
scanning electron microscope examination. 
SEMs have been published only for S. ma- 
calpini Smith (Smith 1979: figs. 24-25) 
and S. westwoodi (Hinton 1981: plate 119). 

Description.—Clavate in shape (Fig. 1), 
nonmicropylar end narrow, slightly arcuate 
ventrally (Fig. 2), sharply pointed in ventral 
view (Fig. 3), blade-like in lateral view 


Photo No.=j}07 LL a 7-Aug-1997 


Figs. 1-8. Egg of Stylogaster biannulata |, Whole egg. ventral view. 2, Whole egg, lateral view. 3, Non- 
micropylar end, ventral view. 4, Non-micropylar end, lateral view. 5, Non-micropylar end, posterolateral view, 
with inset showing surface sculpture of adjacent area. 6, Whole egg, anterolateral view of micropylar end, with 
inset showing surface sculpture of egg body. 7, Surface sculpture of egg body at higher magnitieation. 8, 
Micropylar end, showing concentric surface sculpture. Abbreviations: b, barb; es, eversible sac. 


(Fig. +); with a single pair of small, lateral, 
subapical barbs (Figs. 3-5, b); small ever- 
sible sac present between bases of barbs 
(Figs. 3-4, es), when not inflated this re- 
gion appearing as a cavity (Fig. 5); entire 
surface, except pointed end, with reticulate 
surface sculpturing forming irregular cells, 
the sculpturing strongest and appearing 
scale-like near barbs (Fig. 5), the cells be- 
coming more elongate and less strongly in- 
dicated on main body (Figs. 6, 7), then 
small and roughly concentric around micro- 
pylar end (Fig. 8). Length 0.65 mm (n = 

Remarks.—Unfortunately the eggs we 
examined were embedded in glue on a point 
with the specimen from which they came, 
and we were unable to clean them com- 
pletely. In hydrated specimens, the eversi- 
ble sac appears regularly rounded, as in 
Smith and Peterson (1987: fig. 54.25), not 
irregular as in the SEMs. Lopes (1937) con- 
cluded that the larva enters the host through 
this structure. Rettenmeyer (1961) postulat- 
ed that this sac was inflated when the egg 
was inserted into a host and helped hold the 
egg in place and possibly also absorbed nu- 
trients from the host. Based on osmotic ma- 
nipulations, Stuckenberg (1963) was of the 
opinion that the eversible sac functioned at 
least in part in erecting the lateral barbs. 
Hinton (1981) was skeptical of this theory 
as he thought the barbs were more or less 
immovable. We found some evidence to 
support Stuckenberg’s idea. In Fig. 5, an 
egg in which the sac is not everted, the 
barbs are more closely appressed to the sur- 
face of the egg, while in Fig. 3, where the 
sac is everted, the barbs are more erect. 

How the larva hatches from the egg is 
still uncertain. Rettenmeyer (1961: fig. 1) 
illustrated an egg found on a tachinid with 
a larva just emerging from the micropylar 
end, and therefore discounted Lopes’ 
(1937) theory that the larva emerged 
through the eversible sac. Smith and van 
Someren (1985) also reported observing 
eggs that had embryoes visible inside that 
were facing the micropyle. However, the 


empty eggs of S. varifrons present on cock- 
roach nymphs from which they dissected 
larvae were intact, indicating that the larvae 
had entered the host from near or through 
the sac. 


We examined 29 or 30 puparia obtained 
from the rearings of S. biannulata from 
Gryllus already discussed in the section on 
hosts. All specimens are now housed at the 
National Museum of Natural History, 
Smithsonian Institution, Washington, D.C. 
As this life stage is unknown for any Styl- 
ogaster, we are describing it here. 

Description.—Reddish brown to dark 
brown; ovoid (Fig. 9), surface finely wrin- 
kled with crisscrossing network of slightly 
raised bands (Figs. 10, 11, rb), at higher 
magnification the surface appears more 
deeply wrinkled (Fig. 11); posterior end 
with lateral raised areas that are bilobed 
(nearly c-shaped: Figs. 12, 13), with nu- 
merous raised, cone-shaped tubercles that 
end in a pore (Figs. 14, 15; peg-like exudate 
present in many pores is apparently a result 
of drying); posterior end near apex with 
deep cavity with ovoid opening (Fig. 16); 
inner surface of cavity finely wrinkled 
(Figs. 17, 18), with larger wrinkles more or 
less radiating from slightly depressed 
points. Length 4.3-5.9 mm. 

Remarks.—The structure of the pupar- 
ium closely reflects the larval description 
provided by Smith and van Someren 
(1985). The bilobed, laterally raised areas 
on the posterior end presumably correspond 
to the tracheal system, and the sunken cav- 
ity on the posterior end was also noted in 
the larval description. We were not able to 
describe the larval cephalopharyngeal skel- 
eton that is present inside the anterior end 
of the puparium. It is extremely small, and 
we were not successful in several attempts 
in removing it from the tissue in which it 
was embedded. What we could see corre- 
sponds with the larval mouthparts described 
by Smith and van Someren (1985: figs. 10, 



14-Aug-1997 M 

Figs. 9-14, Puparium of Srvlogaster biannulata. 9, Whole puparium, lateral view. 10, Surface sculpture of 
main body of pupanum. 11, Higher magnification view of surface sculpture of main body of puparium. 12. 
Posterior end of puparium, lateral view. 13, Posterior end of puparium, posterior view. 14, Conical tubercles of 
tracheal tissue on posterior end of puparium. Abbreviation: rb, raised band. 



Figs. t5-18. 
t6, Posterior cavity of puparium. (7, Inner surface of internal cavity of purparium. 18, (nner surface of internal 
cavity of puparium, higher magnification. 

We consider it doubtful that the second 
instar larvae that Rettenmeyer (1961: 1016) 
speculated might be Stylogaster are this ge- 
nus. The large mouthparts and simple pos- 
terior spiracles Rettenmeyer described are 
not at all Tike those of the larvae described 
by Smith and van Someren (1985) and the 
puparia we examined. 


We thank Thomas J. Walker and Susan 
A. Wineriter (University of Florida, Gaines- 
ville) for providing the Stylogaster adults 

Stylogaster biannulata. 15, Conical tubercles of tracheal tissue on posterior end of puparium. 

and puparia as well as information on how 
they were collected and reared. Robert A. 
Wharton (Texas A & M University, College 
Station) provided the specimen with eggs 
for our study. Walter R. Brown and Susann 
G. Braden (Electron Microscopy Labora- 
tory Smithsonian Institution) assisted ma- 
terially with SEM work. Steven W. Linga- 
felter (Systematic Entomology Laboratory) 
helped with scanning some of the SEM im- 
ages into a more usable format. Wayne N. 
Mathis (Smithsonian Institution), Andrew 
V. Z. Brower (Smithsonian Institution). 


Douglass R. Miller, and Allen L. Norrbom 
(Systematic Entomology Laboratory) re- 
viewed the manuscript. 


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