Description of the larva of Somatochlora incurvata Walker (Anisoptera: Corduliidae)

2006·1.5 MB·English

by  Steffens, W P

Odonatologica35(4):379-383 December I,2006
Description of the larva
ofSomatochloraincurvata Walker
(Anisoptera: Corduliidae)
W.P.Steffens¹and W.A.Smith²
'1993HolmRoad,Two HarborsMN 55616,United States
[email protected]
2Wisconsin DepartmentofNaturalResources, BureauofEndangeredResources,
PO Box7921,101S.Webster,Madison WI 53703,UnitedStates
[email protected]
ReceivedApril3,2005/Reviewed andAcceptedAugust18,2005
Thelastlarvalinstarisdescribed andillustrated frommaterialcollected incentral
andsoutheastWisconsin,UnitedStates,andthelarvalhabitatisdescribed.The larva
differsfromrelated speciesin thearcticagroupofSomatochlora inhavingagreater
head width andinthe dorsolateral setal patternsonabdominal tergitesVl-IX.Seg-
ment IXhasdistinctpaireddorsolateral tufts, and VIII,VII,and VIhave progres-
sivelylessdefinedtoabsentpairedtufts.Thesecharactersdistinguishthespeciesfrom
the mostsimilarspecies.S.forcipata,andallothers ofthearcticagroup.
INTRODUCTION
Thelarvaof Somatochloraincurvata Walkerisamongthe lastNorth Ameri-
can membersofthegenustobe described, despitebeing distributedinfairlywell
studiedstates(MA, ME,MI, NY,OH,PA,WI)andprovinces(NB, NS,ON,QC)
(NEEDHAM etal„ 2000). InJuly, 1997,W.A.Smith(WAS) observed S. incurvata
females ovipositing attwo poorfensin JacksonCounty, WI. Six larvalSomato-
chlorain thearcticagroup(WALKER, 1925) were collected atoneof thesesites
by W. Steffens inOctober of 1997, whichcould not be determinedusingexist-
ing keys anddescriptions. Thelarvaefromthis sitewerekeptaliveandrearedby
WAS.FourofthelarvaeemergedinFebruary 1998andweredeterminedtobeS.
incurvata.Theremaining two finalinstarlarvaewere sent toDr Rick Purdueof
the Illinois Museum(ISM)for mitochondrial DNA(mDNA) analysis. mDNA
analysis provides tentativeidentificationoflarval specimens bycomparing base
380 W.P.Steffens&W.A.Smith
pair sequences to those ofknownSomatochloraspecies previously determined
at the ISM(PURDUE, 1998). Theanalyses concludedthatbothlarvae were S.
incurvata.Severaladditionallarvaeandexuvia collectedbetween 1993and2001
werealsoexamined.Thelarvaisdescribedhereandthe diagnosticcharactersare
compared withotherspecies inthe arctica groupofSomatochlora.
SOMATOCHLORA INCURVATA WALKER
Figures 1-2
Material.- UNITEDSTATES,Wisconsin: JacksonCounty,StaffonMarsh,44.35°N,90.67°W,
l-X-1997,1final instar (mDNA);5-X-1997, 1finalinstar (mDNA); 19-X-1997,4exuviae (reared);
JuneauCounty,Necedah National WildlifeRefuge,44.06°N, 90.25°W, 17-V-1999 1final instar,14-
X-1998, 1final instar;OzaukeeCounty,CedarburgBogStateNaturalArea,43.68°N,88.02°W, 26-
VI-1993, 1exuviae. Specimensarein thecollection ofthe Wisconsin DepartmentofNaturalRe-
sources, Bureauof EndangeredResources in Madison.
Larvaewerecollected byvigorouslyscrapingthe sides and undersides ofsubmerged Sphagnum
mossesand sedgeswith astandard aquaticD-net orbyfoot,allowingdebrisand larvaetofall into
the net.Larvae werethenreared toimagoesinsmallaquariums,andexuviae werepreservedinetha-
nol. Larvae used formDNAanalyseswerepreservedin isopropylalcohol.
DESCRIPTION. — The description isbasedon 5exuviae(4 reared) and4last
instars. The diagnostic dorsolateralsetal characteristicsare consistent with 64
additionalS. incurvatalarvaeandexuviae collectedinWisconsinandexamined
by theauthors since 1997.Generalformofthelarvaisconsistentwiththe arcti-
ca groupofSomatochlora, andclosely resemblesS.forcipata (WALKER, 1925).
Thelarvais darkbrown, the
exuviaeislightbrown.
Head.-Verysimilarto S.
forcipata. Antennalsegments
I-IImoderately setose, with
smalllateralandmedialtufts
oflongersetae. Long,finese-
taescatteredelsewhereonan-
tennae. Several (2-3) small,
intraoculartuftsofsetae near
medialline.Posteriormargin
ofheadgentlyconcave,later-
al margins convergent. Lin-
ear fringes ofsetae between
antennae,between eyes, and
along posterior margin of
head,posteriorfringedimin-
ishingorterminating mesad.
Fig. 1.Somatochlora incurvata, lastinstar. Fringes alonglateralmargins
LarvaofSomatochlom incurvata 381
ofhead connect the posterior fringe to the fringebetweeneyes. Dorsal surface
ofheadwithvery shortsetae andsmallbarepatches. Prementumlength usually
equal to or greaterthan width. Prementalsetae 12-14,the fourthto sixth from
the outside being longest. Lateral setae 8-10, usually 9. Palpal crenations 7-9,
eachwith4-5 spiniform setae.
Thorax.- Tuftsofsetae onpronotal and protopleural processes,thoracic
ridges fringed withsetae. Wing padsreaching middleorposteriormarginofVI.
Perimeterof hind wing pads andventral marginof forewing pads fringed with
finesetae.Legs brown, very setose.
Abdomen.- Long-ovate, widest atV-VI, dorsalhooksabsent.Smalllateral
spinespresent onIX only. Venter ofabdomendensely setose withlateralbare
spots. Posteriormarginofsternites fringed withlonger setae. Posteriormargin
ofsterniteIXfringed withvery long setae,extending posteriad beyond thetips
ofthecaudalappendages. Dorsumofabdomenclothedinshortsetae,withbare
spots.Lateralandposteriormargins oftergites fringedwithsetae. Paireddorso-
lateraltuftsoflongersetae onposteriorofmarginofIXandusually VIII distinct
and separated by a zoneofmuch shorter setae.Dorsolateral tufts less distinct
andmediangapprogressively narrowinganteriadfromIX.On VII, tuftsmaybe
indistinctorconfluent, butlongsetae arestillpresentintheconfluencezone.On
VItuftsindistinctorabsent, represented only byafewlongsetae. Inlateralview,
dorsolateraltufts archaway fromdorsumandcurve posteriad.
Caudal appendages. - Cerci usually slightly longerthanepiproct, epiproct of
femalenarrowingrapidly on distalthird,male muchless so. Lateralmargins of
cerci arcuate. Distal margins of superior appendages setose.Paraprocts dense-
ly setose, extending slightly farthercaudadthan superiorappendages in dorsal
view.
Measurements (inmm). —Total length21(18-22);maximum widthofhead6.2(6.0-6.5);
hindwingsheath 6.6 (6,3-6.9);hind femur 5.8(5.7-6.4);hind tibia 6,4(6.3-6.S);prementumlength
(fromarticulationtotipofmedial“tooth”)4.4(4.3-4.S);greatestprementumwidth4.3(4.2-4.4);ab-
domen length11.5(11.3-13);abdomenwidth6.9(6.4-V.6);epiproct 1.2(1.2-1.3);cerci 1.3(1.2-1.4);
paraprocts 1.4)1.3-1.6;lateral spineonIX 0.3(0.2-0.4);tuftsondorsumofIX 1.5(1.3-2.0);poste-
riormarginfringeonsterniteIX 1.5-2.2.5.
breeding HABITAT. — S. incurvataadultshavebeenreported fromnorthern
bogs (NEEDHAM etah, 2000), sphagnum pools (WALKER& CORBET, 1975)
and “sphagnum choked pools inalarge bog... femalesoviposited singly in the
sphagnum pools” in Maine(WHITE, 1969).In Pennsylvania amature female
was seen ovipositing alone in asmallpool beneathleatherleaf, Chamaedaphne
calyculata (L.) Moenchbushes, in a tamarack (Larix) bog (SHIPPER, 1969).
Ourobservations onhabitatsinWisconsinare consistentwiththesesources.
Larvaewere foundinshallow(10-40 cm) water pools, indeertrails,andshal-
low moats thatformat theinterface ofpoorfensand adjacent uplands. These
poorfensare dominatedby Sphagnum mossesandwire-leafedsedges, Carex. C.
oligosperma Michx. ispresent at allsites, and C. lasiocarpa Ehrh. and/orC. ros-
382 W.P.Steffens&W.A.Smith
trataStokesare usuallypresent. Twolarvaewerecollectedinapool immediately
surroundedby sedges only, withnoSphagnum, butSphagnum was present atthe
othersites. Larvaeapparently clingto poorly decomposed peatdebristhatcam-
ouflages them extremely well. ThepH of one pool where larvaewere collected
was 5.6.Thisis probably typical ofthehabitatsinWisconsin.However, wehave
also collectedadultsand observed females ovipositing in shallow trickles with
pH near8.0intheopenportions ofmarly,rich fen-coniferswampcomplexes in
the Upper Peninsulaof Michigan.
HabitatsincentralWisconsinarefoundinlarge wetlandcomplexes onthelake-
bed ofextinct Glacial LakeWisconsin, adjacent to ancient sandy beachridges
forestedwith PinusbanksianaLamb., P. resinosa Aiton, Quercus velutinaLam.
and Q. ellipsoidalis Hill.OtherOdonatafoundinthesamepoolswithS.incurva-
taincludeAeshna verticalisHag.,Leuchorrhinahudsonica(Sel.), Libellulaquad-
rimaculataL., Williamsoniafletcheri Wllmsn,and W.lintneri(Hag.).
DISCUSSION
LastinstarlarvaeofS.incurvata(Figs 1-2)can potentiallybeconfusedwiththose
ofothersinthearcticagroup,butcanbe distinguished asfollows. InS.forcipata
(Scudder), thepaired dorsolateraltufts onabdominalsegmentsVI-IXare quite
distinct,and separated medially by a zone ofshortersetae (Fig. 3).Themedial
zonemaybesomewhatnarrowas intheindividualillustratedhere,orthewidthof
the medial zone may approach
or equal the tuftwidth as illus-
tratedby WALKER(1925).InS.
incurvata the dorsolateraltufts
,
are distinctand well-separated
on IX,andsometimesVIII,but
on VII and VI the tufts are al-
ways progressively less distinct,
closer together, or absent.The
head width of S. incurvata is
greater than 5.9 mm, whilethe
headwidthofS.forcipatais<5.9
mm. S. kennedyi Walker(Fig. 4)
has medialdorsaltufts thatare
not arrangedinlateralpairs. The
abdominal dorsumof S.frank-
Figs2-5. Dorsolateral setal patternsonabdominal seg- lini(Sel.) lacks tufts ofany kind
mentVI-IXof:(2)Somatochlora incurvata;-0)S.for-
(Fig. 5). S. semicircularis (Sel.)
cipata;— (4)S,kennedyi; — (5)S.franklini. —[Setaeon
generalsurfaceoftergitesandcaudal appendagesare also lacks tuftsand the posteri-
omittedfor clarity] orsetae onthe tergites are even
LarvaofSomatochlora incurvata 383
shorterthan thoseofS.franklini, withonlya fewscatteredlong setae (WALK-
ER, 1925). S. semicircularisis a western species; itsrangeand thatof S. incur-
vata donot overlap.
CASHATT& VOGT (2001) provided akey for all knownlarvae ofNorth
AmericanSomatochlora, incorporating our measurements andcomparisons of
S.incurvataandotherspecies inthearctica group.Dorsolateralsetae canbreak
offsometimes, making positive identificationof somearctica specimens a chal-
lenge. However,presenceof setae on posteriormargins ofabdominalsegments
canoftenbe confirmedby thepresenceof definiteinsertionpegs, evenif setae
are missing.
Althoughtime-consumingand tediousto pickthroughpartiallydecayedvegetationlookingfor
larvae,determined effortscanpay off.Properlytimessearchesforexuviaecanalsobeproductive.We
havenowusedthesecollectingtechniquestodocumentover20S.incurvata breedingsitesinWiscon-
sin.The techniquesaresimple,andcanbeused todocumentbreedingoccurrencesandlarvalhabitats
ofanelusiveandlittle-known speciesthatisofconservation concerninmanyareas.
ACKNOWLEDGEMENTS
Thisprojectwassupportedby theWisconsinDNR BureauofForestry, andtheBureau ofEndan-
geredResources’NaturalHeritageInventoryProgram.Thelatteremployedandcontractedthesen-
iorauthorduringthefieldresearch and preparationofthe manuscript. WethankTIMCASHATT,
KURT SCHMUDE,and TIMVOGTforreviewingdraftsofthe manuscript,RICKKOLLATH,
Kollath GraphicDesign,forFigure1,andKENTENNESSENforFigures2-5.
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