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arcuata-group (Odontomyia arcuata-group)
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Odontomyia tumida
Photo#1435209
Copyright © 2017
Joyce Gross
soldier fly -
Odontomyia tumida
-
Benton Crossing Road near alkali lakes, Mono County, California, USA
August 10, 2017
Found on flowering rabbitbrush.
Odontomyia
?
Images of this individual:
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Contributed by
Joyce Gross
on 4 September, 2017 - 1:34am
Last updated 10 September, 2017 - 11:00pm
Moved tentatively to Odontomyia tumida
Moved from
Odontomyia arcuata-group
.
From the relevant keys and descriptions, it appears clear that this is either
O. tumida
or
O. arcuata
.
The somewhat swollen face (i.e. wider and more forwardly projecting than
arcuata
) and the pattern of the black tergal markings seem to suggest
tumida
over
arcuata
here.
…
Aaron Schusteff
, 10 September, 2017 - 11:00pm
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Moved
Moved from
Stratiomyini
.
This indeed keys to
Odontomyia
in the MND
(
1
)
...since the "cross-vein r-m is present": as can be seen in the full-size image as the short "stalk" connecting the small, hexagonal discal cell the the longitudinal vein anterior to the discal cell. (See
this wing diagram
...and compare to
the wing diagram for
Hedriodiscus
, where r-m is absent and the discal cell is directly touching, or confluent, with the radial vein).
Sufficient details are discernible in the images here to go all the way through the
Odontomyia
key
in James
(
2
)
(1936), ending at
O. arcuata
. The
discussion of that species therein
suggests its determination was considered difficult and certain characters mentioned there don't exactly match here. I don't know whether species circumscriptions are "settled" yet here, and I noticed that there is no current guide page for species
O. arcuata
. But there is a guide page for the "arcuata group"...to which this undoubtably belongs, per the key to species groups at the bottom of
page 521 of James(1936)
.
So I'm unsure whether this post should be placed in a new guide page for species
O. arcuata
or not...even though that's pretty clearly where the key in James(1936) leads here. Maybe a stratiomyid expert can clarify that issue?
…
Aaron Schusteff
, 6 September, 2017 - 9:48pm
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thanks Aaron!
Very helpful.
…
Joyce Gross
, 10 September, 2017 - 11:41am
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I'm now mostly convinced this is Odontomyia tumida
My earlier assessment of
O. arcuata
(sensu stricto) was based the long
key in James(1936)
...where
O. arcuata
and
O. tumida
come out in the very last couplet at
the end of the key
via:
28. Face in lateral profile extending forward as far as width of the eye; abdominal bands never contiguous ..........................
tumida
Banks
28'. Face in lateral profile extending forward much less than the width of the eye; abdominal bands often contiguous..............
arcuata
Loew
From your profile shot, I measured the face extending forward a bit more than half the eye length (i.e. 7/13 ≈ 0.54, or "much less than the eye width"), so I went with
arcuata
.
But...
today I carefully went through the keys in James(1960)
(
1
)
, and found that, using that reference, your photos lead to genus
Eulalia (= Odontomyia)
, and species
E. tumida
. There the couplet separating
tumida
from other members of the "
arcuata
group" is:
11. Lower occular orbits divergent (figs. 34, 35), the sides of the face in the female, as well as in the male, likewise divergent; face entirely yellow except somtimes two small spots above the tentorial pits; abdominal terga with black transverse basal bands, strongly biarcuate posteriorly, in both sexes, those of the male connected on a median line with those of adjacent segments....
tumida
11'. Lower occular orbits, along and just above the oral margin, parallel (figs. 31, 32); sides of face of female approximately parallel; face often marked with black or wholly black. ................12 (leading to
inaequalis, communis, alticola
and
arcuata
)
The face and lower (inner) margins of the eyes in your photos appear divergent, and indeed they match the female of
tumida
shown in Fig. 35 of James(1960)
(
1
)
, better than the female of
(arcuata) communis
shown in Fig. 31. And, even better than those figures from James(1960), consider the frontal type specimen images below from the MCZ:
tumida
arcuata
In addition to James(1960), I was also able to obtain the key in
James(1974)
, where your post here goes promptly to
tumida
, via:
1. Sides of face broadly diverging all the way to the lower margins of the eyes; in males, distance between the lower angles of eyes distinctly longer than vertical distance from that plane to bases of antennae ........ 2
1'. Sides of face parallel or almost so on lower part opposite oral margin, in females slightly convergent; in males distance between the lower angles of eyes no greater than vertical distance from that plane to bases of antennae; eyes bare............3 (leading to
cincta, inaequalis continua, inaequalis communis, inaequalis inaequalis, arcuata arcuata, arcuata alticola
and
arcuata occidentalis
)
2. Eyes hairy; face marked with black, usually conspicuously so. ................
hirtocculata
James
2'. Eyes bare; face wholly yellow or green. ................
tumida
Banks
Note that the character "Face in lateral profile extending forward as far as width of the eye", which was emphasized in the 1936 key...and also appears in the descriptions of
tumida
given in Bank(1926) [see
here
] and James(1936) [see
here
]....was
not
repeated in the 1960 and 1974 keys. I'm thinking that character was overstated in the keys and descriptions prior to 1936. The epithet
tumida
is latin for "swollen"...and indeed, studying the MCZ type images below for
tumida
and
arcuata
:
tumida
arcuata
...one sees the face of the former is more "forwardly swollen" than that of the latter. BUT, the face does
not
extend forward a "full eye's-width" in the
tumida
type image...rather it extends 2/3 (≈0.66) the eye width. And while the face extends your photo extends forward only 0.54 of the eye width, it's still substantially "swollen" compared to the type of
arcuata
.
Another significant character supporting
tumida
is the shape of the black markings on the abdomen. For
tumida
they're
described in James(1936)
as follows:
"segments two to five with black transverse bands which are usually confined to the basal half and never contiguous with the lateral margins nor with the bands of the adjacent segments; those on segments two and three strongly biarcuate on the posterior margins; that on four less so; that on five semi-elliptical"
Your photos very much conform to the above...whereas the
description of
arcuata
in James(1936) indicates its black tergal bands are "often connected medially with the bands of adjacent segments". Again, compare dorsal images of the MCZ types with your female:
tumida
arcuata
Nearly everything (keys, descriptions, type images) supports
O. tumida
here...the only descrepancy seems to be the black markings just above the antennae: as in the type images above, for
tumida
they're described as being two separate lateral spots contiguous with the eyes; whereas in
arcuata
they're joined as a single "very broad" transverse marking above the antennae. In your photos the two spots are joined by a narrowed band. This appears to be more in line with the character state for
arcuata
. My guess it this discrepancy can be attributed to "variation". Overall, the stronger match seems to clearly be with
tumida
.
One last thing...the following quote is from Cole
(
2
)
(1967):
"
O. tumida
Banks(1926) was described from Calif. specimens and is a rather common autumn species in that state; the known range is from Wash. and Mont. to Kansas. Banks stated that nearly all specimens going under the name
arcuata
were referable to
tumida
, but it might depend on the dipterist doing the naming."
…
Aaron Schusteff
, 10 September, 2017 - 9:21pm
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Moved
Moved from
Soldier flies
.
…
John S. Ascher
, 4 September, 2017 - 7:24am
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