A description of the larva ofHeliaeschna uninervulataMartin (Odonata: Aeshnidae) from Singapore, with notes on its relationships

2011·0.19 MB·

by  Albert G. Orr

InternationalJournalofOdonatology
Vol.14,No.2,June2011,163–169
A description of the larva of Heliaeschna uninervulata Martin
(Odonata:Aeshnidae) from Singapore,
with notes on its relationships
AlbertG.Orr*a andRobinW.J.Ngiamb
aGriffith,SchooloftheEnvironment,GriffithUniversity,Nathan,Q4111,Australia;bNationalBiodiversity
Centre,NationalParksBoard,SingaporeBotanicGardens,1ClunyRoad.S(259569),Singapore
(Received7February2011;finalversionreceived3March2011)
ThelarvaofHeliaeschnauninervulataisdescribedandfiguredforthefirsttime.Itscharactersmostly
fallwithinthelimitsofvariationofGynacanthaspp.ComparisonofthelarvalcharactersofH.filostyla,
theonlyothermemberofthegenusforwhichthelarvaisknown,suggeststhatitisnotcongenericwith
H.uninervulata.
Keywords: Odonata;dragonfly;larva;Aeshnidae;Heliaeschna;Gynacantha;Singapore
Introduction
ThegenusHeliaeschnaSelys,1881presentlyincludessome11–16recognisedspecies,10from
tropicalAfrica(consideredbyDijkstra[2005]torepresentjustfivespecies)andsixfromsouth-
eastAsia.ThegenushasgenerallybeenconsideredtobecloselyalliedtoGynacanthaRambur,
1842,andwaserectedprimarilyonthebasisofvenationaldifferencesfromthatgenus,withthe
medianspacebeingcrossedatleastonceinHeliaeschna,whereasinGynacanthaitisfree.Ithas
beenremarkedbyLaidlaw(1923)andDijkstra(2005)thattheAfricanandOrientalspeciesshow
littlesimilarity.InparticulartheventraldentigerousplateonS10ofthefemalebearstwospines
inAfricanspecies,thesamenumberasGynacantha,but3–6spinesinOrientalspecies.
Todatethelarvahasbeendescribedforjustonespeciesofthegenus,H.filostylaMartin,1906,
from Sulawesi (Kawashima & Sasamoto, 2007). This species has long been considered to be
dubiouslyplacedwithinthegenus(Lieftinck,1937),thusnolarvaofanundisputedmemberof
thegenushashithertobeenknown.Itistobehopedthatlarvalcharactersmayhelpusunderstand
the relationships within the genus, and ultimately, whether Ethiopian and Oriental species are
indeedcongeneric.RecentlyRWJNsucceededinbreedingafemalespecimenofH.uninervulata
Martin,1909,fromanF-4stadiumlarvadiscoveredinaleaflitteredforestpoolofasecondary
forest within Central Catchment Nature Reserve of Singapore, and the larva is here described
fromtheexuvia.
*Correspondingauthor:26CurrimundiRd,Caloundra,Q4551,Australia.Email:[email protected]
ISSN1388-7890print/ISSN2159-6719online
©2011WorldwideDragonflyAssociation
DOI:10.1080/13887890.2011.575729
http://www.informaworld.com
164 A.G.OrrandR.W.J.Ngiam
TheadultspecimenrearedrepresentsthesecondrecordofH.uninervulatafromSingaporeand
thefirstspecimencollected,thefirstrecordbeingbasedonaphotographofanovipositingfemale
(Tang,Wang&Hämäläinen,2010).Thespeciesisunusualamongmembersofthegenusinthat
themedianspaceiscrossedbyjustonevein.Alsothearmatureofthedentigerousplatewith3–4
short spines in a single row (Lieftinck, 1953), three in the present specimen, differs from most
otherOrientalmembersofthegenuswhichhavefourspinesintworowsoftwo.
Areaandmethods
A single larva (F-4) was collected using a tray net from among leaf litter in a forest pool.The
location is in the secondary forest of the Chestnut streams system within Singapore’s Central
Catchment Nature Reserve.The larva was returned to laboratory and reared to emergence in a
smallplasticaquariumtank(15×8×9cm)half-filledwithwater.Someleaveswereprovided
as substrate with a wooden stick added in as a support during emergence. The larva was fed
almostwhollyonTubifexworms,Tubifextubifex(Müller,1774).Onlyononeoccasionwasthe
larva offered small fry of the Mosquito Fish (Gambusia holbrooki Girard, 1859). The exuvia
was examined and dissected under a stereo microscope and figures prepared with the aid of a
drawingtube.
Materialexamined
1(cid:2)exuvia(reared),collectedasF-4larva,14July2010,Singapore,forestpoolatChestnutstreams
withinCentralCatchmentNatureReserve,RWJNleg.,emerged12September2010.
Description
Diagnosis
Habitustypicallyaeshnid;headratherlarge,legsmoderatelylong,abdomenfusiformwithvery
long anal appendages. Coloration generally dark brownish grey with pale mottling (Figure 1).
Bodysurfacegenerallyfinelypilose,withscatteringofshort,moderatelysparsesetae.
Head
Large,roughlypentagonal,withveryprominenteyes.Postocularlobeswelldevelopedandevenly
rounded. Slightly raised suboval areas immediately behind bases of eyes, oblique patch across
baseofpostocularlobes,areasofvertexandcentreoflabrumglabrous.Antennasevensegmented
(S6–7missingonbothsidesonexuviabutclearlypresentonaphotographofthelivinglarva);S1
andS2dark,broadandshort;S3pale,c.twicelengthandhalfwidthofS2;S4andS5c.halflength
ofS3,palewithdarkbands.Prementum(Figure2a)ofmoderatelengthandbroaddistally;distal
onethirdoflateralmarginswithfineforward-pointingserrationsinterspersedwithsparsesetae;
distal(anterior)marginveryslightlyconvex,withdensefringeofshortfinesetae;mediancleft
veryshort.Labialpalpterminatinginlong,broadflattened,securiforminnerprocess,producedto
formashortinnerhookapically;entireprocesswithfinelyserrateinnermargin.Medianpartof
palpbearingfiveverylong,strongsetaearisingfromitsinnersurface,theanteriortwoextending
beyond the distal margin of the securiform process. Movable hook moderately short and stout,
bearingadistinctrowofveryfinesetaefortwothirdsofitslength.
Adescriptionofthelarvaof Heliaeschnauninervulata 165
Figure 1. Heliaeschnauninervulata♀exuvia,habitus,dorsalview.
Thorax
Relatively short and narrower than head. Pronotum shield-shaped, terminating in two lateral,
forward directed processes dorsally, visible as the posterior prothoracic process in Figure 1;
ventrolaterallyprothoraxwithtwosubequalfinger-likeprocessesabovecoxabearingmoderately
longpalesetaeandseveralsmallspines(Figure2b);(inFigure1onlytheanteriorpairisvisible,
the posterior pair lying under the dorsal shield); space between two forming a ‘U’shape. Legs
moderatelylong,asshowninFigure1,distinctlybanded.Wingsheathsreachinganteriormargin
ofS4oralittlebeyond;distinctlybanded.
Abdomen
Moderatelyhighinprofile,insectionasomewhatflattenedinvertedcatenaryshape.Dorsalspines
absent. In dorsal view strongly fusiform. S5–9 with short ventrolateral spines (Figures 1, 2d).
166 A.G.OrrandR.W.J.Ngiam
Figure 2. Heliaeschna uninervulata ♀ exuvia: (a) dorsal view of mask with prementum and labial palps; (b) right
propleuralprocessesimmediatelyaboveprothoraciccoxa;(c)S9–10+analappendages,dorsalview;(d)S8–10+anal
appendages,ventralview.
Appendages(Figure 2c)verylong;epiproct2.2timeslengthofS10,terminatingbluntly.Para-
proctsslightlylonger,terminatinginasharppoint;innerandoutermarginsweaklyserratewitha
fewlongfinesetaeandasparsecoveringoffineshortsetae.Cerciverylong,almostreachingend
ofparaproct,slightlyhookedinwardtowardthetipandterminatinginasharppoint.Gonapophy-
ses (Figure 2d) extend for full length of sternum of S9 and overlap first quarter of S10; outer
gonapophysesextendingalmosttotipsofinnergonapophyses.
Measurements(mm)
Totallength30;headwidth7.3;pronotumdorsalwidth4.9;lengthofparaprocts3.6.
Habitatandbehaviouralobservations
The female larva was found in a pool near a forest stream. The pool was about 1m deep and
filledwithdenseleaflitter,fallentwigsandbranches.Theunderlyingsubstratewasmuddy.The
surroundingforestwasmainlysecondarywithasmallsandystreamflowingby.
Adescriptionofthelarvaof Heliaeschnauninervulata 167
Incaptivity,theF-4larvaspentmuchofthetimegraspingontoawoodenperchfacingupwards
nearthewatersurfacewithitsbodyheldclosetothewood.Itremainedcompletelysubmergedand
motionlessinthisambushstance.Occasionally,itwouldturnaroundtoadoptthesamestancebut
facingdownwards.PreyintheformofTubifexwormswereseizedwithaquicklabiumstrike.If
preywasoutoflabiumreach,thelarvawouldmoveactivelytowardsit.Ontheonlyoccasionwhen
smallfryofMosquitoFish(Gambusiaholbrooki)wereoffered,thelarvamovedseveraltimesto
adoptdifferentambushpositionsalongtheperchuntilitsuccessfulcapturedthisprey.Allprey
wasconsumedunderwater;thelarvaneverdisplayedsemi-terrestrialbehavioursuchasdisplayed
byTetracanthagynaplagiatalarvae(Orr,Ngiam&Leong,2010).Faeceswereprojectedoutof
waterontothetanksurface.Whenapproachedbyaforeignobjectsuchasapairofforceps,the
larvashowedanti-predatorbehaviourbyswivellingtotheothersideoftheperchthusconcealing
itselffromview.
Thelarvawasfedalmostdailyresultinginrapidgrowth.FromF-4larva,itmoultedtoF-3on
18July2010,F-2on25July2010,F-1on2August2010andfinallytoFstadiumon18August
2010. The moulting process to F stadium was witnessed at around 08:00h. The larva moulted
whilefacingdownwardsperchedontothewood.Attheendofthemoulting,thelastpieceofthe
exuviahangingbytheabdomentipwasdiscardedwithaforcefulflick.Thisactionthrewtheold
moultsomedistanceawayfromthefinalinstarlarva.
Transformationoccurredintheearlyhoursof12September2010.Whenobservedataround
08:30hrs,theadultwasfullyemergedwithwingsopened.
Discussion
InitsgeneralformthelarvaofH.uninervulataexhibitsarangeofcharactersentirelyconsistent
withthoseknownforvariousspeciesofGynacanthaandrelatedgenera.Typicalfeaturesinclude
the large head, prominent eyes, large rounded postocular lobes, sculpturing of the prothorax,
elongateanalappendagesandsmallposterolateralspinesonabdominalsegments5–9,(sometimes
6–9inGynacantha–e.g.Matsuki,1986b).Moreover,acloseaffinitywithGynacanthaisindicated
bythefivelargesetaeonthelabialpalp.AsfarasisknownthischaracteroccursinallGynacantha
speciesalthoughtheactualnumberofsetaemaybefewerasinG.hyalinaSelys1882(Matsuki,
1986b),G.basiguttataSelys,1882(C.Y.Choongpers.comm.)andvariousAustralianspeciesas
describedandfiguredbyTheischinger(2002)andTheischinger&Endersby(2009).Indeedthe
setaeonthelabialpalpsareprobablyaslongandatleastasstoutasinanyhithertoknownaeshnid
larva,andareexceededinnumberbyonlyafewspecies,suchasAustrogynacanthaheterogena
Tillyard,1908,TriacanthagynaspeciesaspresentedbyHeckman(2006),G.dobsoniFraser,1951
andG.rosenbergi Kaup,1857(TheischingerandEndersby,2009).G.japonica Bartenef,1909
alsobearsfivelargesetaebuttheseareshorterandfiner(Matsuki,1986a).Theslightlyconvex
anterior margin to the prementum is typical of Oriental and Australian Gynacantha as is the
securiformshapeoftheinnerprocessofthelabialpalp.CertainGynacanthaspeciesbearasmall
toothontheanteriormarginoftheprementumoneithersideofthemediancleft.Howeverthis
is lacking or vestigial in many species, such as G. japonica, in which the form of the mask is
almostidenticaltothatofH.uninervulata.Theprothoracicprocessesaredistinctlythinnerthan
inH.filostyla orG.rosenbergi (Theischinger,2007),thespacebetweentheiradjacentmargins
being‘U’-shapedasopposedtoa‘V’-shapedinthosespecies.NeverthelessiftheexuviaofH.
uninervulatahadbeendiscoveredwithoutanassociatedadult,itwouldhavebeenlogicaltoassign
ittoGynacantha.
TheformofHeliaeaschnalarvadescribedhereisconsistentwiththecloserelationshipbetween
thisgenusandGynacanthaidentifiedbyvonEllenrieder(2002).Howeveritshowsfewersimi-
laritieswiththelarvaofH.filostyla,describedbyKawashina&Sasamoto(2007).Inparticular,
168 A.G.OrrandR.W.J.Ngiam
theformofthemaskofH.filostylaisunlikethatofH.uninervulataoranyknownGynacanthaor
ofAustrogynacanthaheterogenaTillyard,1908.Firstly,atthebaseofthelabialpalpandnearthe
outeranteriormarginoftheprementumaresmallarticulatingspurs,alsopresentinPeriaeschna
laidlawi(Förster,1908)(Kawashima&Sasamoto,2006)andTetracanthagynaSelys,1881spp.
(Orretal.,2010),butabsentfromH.uninervulataorGynacanthaspp.Secondly,theinnerprocess
ofthelabialpalpisratherhook-shaped,tendingmoretotheformfoundinP.laidlawi,oratits
mostextremeinTetracanthagyna,thaninH.uninervulataorGynacanthaspp.Thirdly,theanterior
marginoftheprementumisdeeplyincisedaroundthemedianclefttoformaroundedVleading
into the cleft and on either side are two short rounded processes well removed from the cleft;
marginalsetaearedenseandmoderatelylong.Thesecharacters,especiallythemid-lateralpro-
cesses,occurvariouslyandprobablybyconvergenceinPeriaeschanaMartin,1909(Kawashima
&Sasamoto,2006;Matsuki&Lien,1984)andPlanaeschnaMcLachlan,1892(Matsuki,1989),
butnotinH.uninervulataorGynacanthaspp.Finally,inH.filostylaallsetaeonthelabialpalp
are short and fine, although their position possibly suggests they may be homologous with the
largesetaeofH.uninervulata.Intheirdiscussion,Kawashima&Sasamoto(2007)suggestapos-
siblerelationshipbetweenH.filostylaandtheNewGuineagenus,PlattycanthaLieftinck,1937,
thelarvaeofwhichremainunknown.ThiswasbasedmainlyonacommentbyLieftinck(1937)
buttheideahasbroaderacceptance(G.Theischingerpers.comm.6/12/2010).Thetaxonomyof
thegenusPlattycanthaFörster,1908isprobablynotyetresolved,andtherelationshipsbetween
thespeciesofthisgenusandH.filostylaareworthinvestigating.Furthermore,itwillbeofcon-
siderable interest to examine the larvae of other Oriental and alsoAfrican Heliaeschna species
oncetheyarediscovered.AtpresentmostOrientalmembersofthegenus,includingH.bartelsi
Lieftinck,1940,H.crassaKrüger,1899,H.idae(Brauer,1865),H.simplicia(Karsch,1891),but
excludingH.filostyla,canbemaintainedasaseparategenus(althoughpossiblynotHeliaeschna
asthenominotypicspecies;HfuliginosaSelys,1883mayinfactbelongtoGynacantha–Dijkstra
[2005])onadultcharacters,especiallythearmatureofthedentigerousplateoffemaleS10,butthe
larvalcharactersofH.uninervulataareclearlynotsufficientforseparatingthegenera.Itshould
howeverbenotedthatinotherOrientalspeciespresentlyincludedinthegenusthedentigerous
plate has two rows of spines rather than one row, suggesting a relatively distant relationship to
H. uninervulata. Thus there is a possibility that Oriental Heliaeschna as currently recognised
representsatleastthreedifferentgenera.
Acknowledgements
WethankinparticularAkihitoSasamotoandGuntherTheischingerforsupplyingliteratureandforhelpfuldiscussions.
Inaddition,themanuscripthasbeengreatlyimprovedbythecarefulandcriticalcommentsofboth.KarenTeo,James
Gan,SharonChanandcolleaguesfromCentralNatureReserveNparkssupportedthestreamsurveywhichledtothis
larvadiscovery.
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