An Atypical Larval Color Form Of Baetis Intercalaris (Ephemeroptera: Baetidae) From Pennsylvania And The Kiamichi River Basin Of Southeastern Oklahoma

5 Pages·1996·1.5 MB·English

by  R D Waltz

Vol. 107,No.2,March&April, 1996 83
AN ATYPICAL LARVAL COLOR FORM OF BAETIS
INTERCALARIS (EPHEMEROPTERA: BAETIDAE)
FROM PENNSYLVANIAAND THE KIAMICHI RIVER
BASIN OF SOUTHEASTERN OKLAHOMA1
R.D.Waltz2,D.E.Baumgardner3-4,J.H.Kennedy4'5
ABSTRACT: An atypical larvalcolorformofBaetisintercalariswasdiscoveredandreared from
theKiamichiRiverbasinofsoutheasternOklahoma.Identicalnymphswerealsorecentlydiscovered
in northeastern Pennsylvania. This atypical larval color form has been previously reported only
fromWisconsin.Larvaeofthiscolorformarevisuallydistinctivebecausetheylackthepaletriadof
spotsalongthe posteriormarginsofmostabdominal tergitesdiagnostic ofthetypical colorform.
The atypical form is uniformly marked on each tergite with pale, anterior, paired incurved lines
(parentheses like) on agrayorbrown background, lacking the palerabdominal tergites and spots
characteristicoftypicalB. intercalaris.Nomorphologicalcharactersintheadultstageorthelarval
stagewerefoundtosupportestablishmentofanewspecies.
Independently conducted ecological studies of the macroinvertebrates in-
habiting two disjunct riversystems ofNorthAmerica resulted in the collection
ofa little reported form ofBaetis intercalaris McDunnough. This larval color
form is characterized by its lack of well developed and contrasting color pat-
ternsofthe abdominal tergites when compared with the typical color form (see
Moriharaand McCafferty 1979). Bergman and Hilsenhoff(1978) firstreported
this unpatterned form in their studies of the Wisconsin Baetidae. The unpat-
terned form is visually distinctive in field samples and is readily identified as
unique due to the flat gray or brown, non-contrasting background color of the
abdominal tergites (Fig. 1), typical "intercalaris" type of prothorax pattern
(Moriharaand McCafferty 1979), and medially banded cerci and terminal fila-
ment. No otherBaetis species in NorthAmerica is similarly colored.
Larval specimens ofthe unpatterned form ofB. intercalaris were collected
andreared (by DEB) from the Kiamichi Riverbasin ofsoutheastern Oklahoma.
Another series of identical specimens was collected and brought to the atten-
tionoftheseniorauthorbyJamesB. Munro,EastStroudsburgUniversity,based
on material that hecollected in northeastern Pennsylvania. In each ofthe above
cases, the unpatterned larval form was theonly color form ofthis species found
1 ReceivedOctober 14, 1995.AcceptedNovember6, 1995.
2 IDNR, Division of Entomology and Plant Pathology, 402 West Washington, Room W-290,
Indianapolis, Indiana46204.
3 PresentAddress:9015RockCliff,SanAntonio,Texas78230.
4Department ofBiological Sciences, University ofNorth Texas, P.O. Box 5218, Denton, Texas
76203.
5 Present Address: Department of Biology, University ofTexas Pan American, Edinburg, Texas
78539.
ENT. NEWS 107(2): 83-87,March&April. 1996
84 ENTOMOLOGICALNEWS
atthesite.TypicalcolorformsofB. intercalariswerenotpresentinsiteswhere
collections were made ofthe unpatterned form.
MATERIAL EXAMINED
Material which formed the basis for this report includes the following lar-
val, adult, and reared adult specimens:
OKLAHOMA: Pushmataha Co., Kiamichi R. at Hwy 2, 16.3. mi N Hwy 2-3 jet, D.E.
Baumgardner, 16-IX-1993, 2L, and 14-X-1993, 2 reared male adults, 1 reared female adult, 7L.
OK: LeFloreCo., Kiamichi R.atHwy259,approx.0.5miSHwy63-259jeWt, 18-VII-1993,D.E.
Baumgardner,2L.OK:LeFloreCo.,PigeonCrkatHwy63,approx.5.5mi Oklahoma-Arkan-
sasborder, 19-VI- 1993, D.E. Baumgardner, 1 maleadult. OK: PushmatahaCo., Dry Crkatun-
named lowwatercrossing,approx.2.5miETuskahoma, 17-VII-1993,D.E. Baumgardner, 1L.
PENNSYLVANIA: PikeCounty, BloomingGroveCreek,6,27-VII 1993; 10,24-VIII-1993;
9-IX-1993,and4-X-1993,JamesB. Munro.
Representative vouchers havebeen deposited in thePurdueEntomological
Research Collection, West Lafayette, Indiana, and University ofNorth Texas,
Denton, Texas.
IDENTIFICATION
Larvae of the unpatterned form will reach an impasse in the key couplet
separating Baetis intercalaris from B. flavistriga McDunnough in Morihara
andMcCafferty(1979:couplet 19)becausethetergalpalespotsarenotpresent.
To accommodate identification ofthe unpatterned form, couplet 19 ofthe key
may be modified to read:
19. Darker,well-markedabdominaltergiteswithtwolargesubmedianpaleareas,oftenkidney
shaped B.flavistriga
19'. Darker, well-marked abdominal tergites with 3 posteriorround pale areas, middle spot
often smaller than laterals or abdominal tergites uniformly gray or brown with pale
parentheses-likemarksatmiddle,anteriormarginofeachtergite B. intercalaris
Confirmation oftentativelarval identifications using this modifiedcouplet
shouldcontinuetobeaccomplished by usingtheexpandeddiagnosis underthe
species discussion ofB. intercalaris in Morihara and McCafferty (1979). In
some specimens, the slide mounted larval exuviae of the unpatterned form
showed indication ofpale tergal areas on the anterior tergites when examined
with indirect substage lighting.
The adult ofthe reared, atypical larva keys readily toB. intercalarisin the
most recent keys to theBaetis species adults (Traver 1935) based on the elon-
gated marginal intercalaries of the first interspace in the forewing. However,
adults ofthe reared atypical specimens possessed adark-brown thorax, rather
Vol. 107,No.2,March&April, 1996 85
Figure 1.Baetisintercalaris(unpatternedform). Dorsalhabitus(photograph).
86 ENTOMOLOGICALNEWS
than the black thorax of typical B. intercalaris. Such color differences in the
adult stage have been regarded as within the observed limits of intraspecific
variation in closely allied species, e.g., B. flavistriga (see Morihara and
McCafferty 1979 and Traver 1935) and in Baetis dubius (Walsh) (Waltz, per-
sonal observation). Furthercomparisons ofthe adult male reared from the un-
patternedlarvalformwithadultmalesrearedfromtypicalB. intercalarislarvae
showed nodiscerniblemorphological differences.
BIOLOGYAND DISCUSSION
Baetis intercalaris, widely distributed in the Kiamichi Riverdrainage, was
collectedfromthirdthroughfifthorderstreamsin theupper,middle, andlower
reaches ofthedrainage. Larvae were collectedfrom gravel/pebble substrate in
riffles. Other studies have reported similar habitats for this species (Bergman
and Hilsenhoff 1978; Bernerand Pescador 1988).
BaetisintercalarismayhavetwogenerationsperyearintheKiamichiRiver
drainage, consisting of a spring and a fall generation. Immature larvae were
first collected in June 1993, with late instar and emerging larvae collected in
October, indicating the fall generation.Although no larvae were collected be-
foreJune, asingle adult wascollected inJune 1993, suggesting theoccurrence
ofa spring generation. In the northern regions ofits range, B. intercalaris has
been reported variously as univoltine (Bergman and Hilsenhoff 1978; Harper
and Harper 1984), or bivoltine (McDunnough 1921, 1923; Ide 1935). Emer-
genceofB. intercalarisoccursthroughouttheyearinthesouthernregionsofits
range (Berner and Pescador 1988), and often has no cohort synchronization
(Jacobi and Benke 1991).
Thecauseoftheatypicalcolorvariation isunclearatthistime.Theatypical
colorformcouldrepresentacrypticspecies.Asecond,andmoreprobablecause,
is that this atypical color form may be a result ofsome, as yet not identified,
environmental factor causing the differences in color. Not only are there no
obvious morphological differencesin thetypical versus theatypical forms, but
thepresenceofpatterningcommon tothetypical form, thatis vaguelydiscern-
ibleinatleastsomelarvaeoftheatypical form,leadsustoseekanenvironmen-
talcausefortheatypicalcoloration.Alloftheunpatternedformlarvaereported
hereinwerecollectedinthemidtolatesummer,orthesecondgenerationcycle.
Noearlier, orspringgeneration, collectionsofthe unpatterned formare known
to us. Additional studies, including rearings ofboth typical and atypical color
formsfrom throughouttherangeofthisspecies,andlifehistory studies, willbe
required to better understand the source ofthis atypical coloration.
ACKNOWLEDGMENTS
We thank James B. Munro and Bruce Haase, East Stroudsburg University, PA, for making
theirmaterialofBaetisintercalaris(unpatternedform)availableforstudy.
Vol. 107,No.2,March&April, 1996 87
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