Key to the larvae of European Orthetrum Newman (Anisoptera: Libellulidae)

6 Pages·1993·0.73 MB·English

by  Butler, S G

Odonalologica22(2): 191-196 June I. 1993
Key tothe larvaeofEuropeanOrthetrum Newman
(Anisoptera: Libellulidae)
S.G. Butler
Red Willow,AllStretton,Shropshire, SY66HN,
United Kingdom
Received October8, 1992 /Revised and AcceptedDecember 14, 1992
Based onlaboratoryreared material,adescriptivekey ispresentedofthe ultimate
instarlarvae(exuviae)of8 spp.,viz.albistylum(Sel.),anceps (Schneider),brunneum
(Fonsc.), cancellatum (L.), chrysostigma (Burnt.), coerulescens (Fabr.),nitidinerve
(Sel.)andtrinacria(Sel.).Thepreviousdescriptionsarecriticallydiscussed,andsome
additional structural features forspeciesseparationarestated.
INTRODUCTION
Current available keys to the European Orthetrum larvae are eitherregional
or selective: GARDNER, 1954 (UK.); CONCI & NIELSEN, 1956 (Italy);
FRANKE, 1979(Central Europe); CARCHINI, 1983(Italy); BELLMAN 1987
(Central Europe); CONESAGARCIA 1990(Spain).
ASKEW (1988) draws together a selection ofpublished larval keys, but ex-
cludes O. trinacriaandO. anceps.CONCI & NIELSEN (1956) figure detailed
illustrations, including amuchcopied atypical labiumofO. coerulescens (p.265
fig. 149 andexplained p. 266 note [1]). CARCHINI (1983) does not appear to
separate O.ancepsandO. coerulescens, particularly withrespectto thepresence
or absence of dorsal abdominal spines (cf. BUTLER, 1992).KUMAR (1971)
states that O. brunneumhas large dorsalabdominalspines — certainly not the
case inEuropean individualsofthisspecies, although this is a featureon which
FRANKE (1979)isalsounclear — andBELYSHEV(1973)describesitashaving
no lateralspines.
O. nitidinervehasbeen describedaseitherhavingno lateralspines (CONESA
GARCIA, 1990),or lateralspines only on segment 8 (NIELSEN, 1955),larvae
andexuviaeexaminedhave shownthesedetails so fartobe incorrect(BUTLER,
1992).
192 S.G. Butler
With these current ommissions and contradictions in mind, a first attempt is
madetoproduce akey tothelarvaeoftherelatively fewbutproblematic European
species ofthis genus.
MATERIALAND METHODS
LarvaeofalleightspecieswererearedinUK.Adults wereobtainedfromallexcept forO.trinacria,
larvae ofwhich died atF-1. The distinctive exuviae ofthis species wereobtained fromasitewhere
it wasflyingin numbers. Material waspinned, cleanedand setwith thelabiumextended, but not
flattened. Itwasthen examined usingx4O magnification.
O. albistylum (Sel., 1848). Brenne, France, 13-VIII-I989;- Aliakamon River.Thessalo-
niki, Greece, 28-VII-1992. [II larvae,3exuviae].
O. brunneum (Fonsc., 1837).- RiverVerdoule,Quissac,France,10-VIII-1989; - Aliakamon
Delta, Thessaloniki, Greece, 21-VIII-1990; - El Burgo,Andalucia, Spain,20-VIII-1991. [l2
larvae, 14exuviae].
O. cancellatum (L.,1758).- Brenne,France, 13-VIII-I989; AliakamonDelta,Thessalo-
niki, Greece, 21-VIII-I990; - Adra, Spain, 27-VIII-I99I; Henlow, Bedfordshire, UK, 29-VI-
-1979. [22 larvae, 41 exuviae].
O. chrysostigma (Burnt., 1839). EIBurgo,Andalucia,Spain,20-VII-1991,25-IX-1992,
J.Mason). [9 larvae, 10exuviae],
O. coerulescens (Fab., 1798). Albufuera, Majorca, Spain,28-VIII-1987; Cramer
Gutter,Shropshire,UK, 13-VIII-I99I; New Forest,Hants,UK,I-VIII-1982. [29larvae,56exu-
viae].
O. nitidinerve (Sei., 1841). Churriana, Malaga,Spain,20-IV-1990, 21-VII-1991. [3
larvae, 3exuviae].
O. anceps (Schneider, 1845). Stavros, Thessaloniki, Greece; 10-VIII-1990,4-VIII-1992;
- PetresRiverGorge,Rethymnon,Crete,Greece,6-IV-1991,R.G. Kemp). [l2larvae,lOexuviae].
O. trinacria (Sei. 1841). Adra, Spain,27-VIII-1991. [3 larvae,20exuviae].
Althoughthe numberand distribution oflabialandmentalsetaeareimportantspecificcharacteris-
tics, afew individuals show slightvariations inthisrespect, therefore other featureshave beenused
asprimaryseparationcharacters where possible. Alsoshortdescriptions have been added in order
toreinforceidentification.
Maximum/minimum publishedlengthsaregiven,however the overlappingofrelatedspeciesand
the tendancy ofboth larvae and exuviae totelescope reduces the value ofprecise measurement as
an identification feature. Finallythe needto prepare specimensin order to check thepresence or
absence ofabdominalspines(BUTLER, 1992),cannotbe overstressed.
DESCRIPTIVE KEY
I Some abdominal segments with dorsal spines 2
No dorsal abdominal spines 4
2 Finalinstars smallerthan23mm. Dorsal spinesonsegments 4-7, labial palps with 3 (rarely4)
setae(Fig.5) coerulescens
(Dorsal spines often hiddenby dirtand surroundingsetae. Midtodarkbrown,epiproctrelatively
short, length 16-20 mm).
Final instars largerthan 23 mm 3
3 Dorsal spinesonsegments6,5and4(Fig.I).Ratiolength/widthofepiproct~2 cancellatum
(Paired spots noticeable on the dorsal abdominal surface ofclean larvae and exuviae (Fig.2);
Larvalkey ofEuropean Orthetrum 193
Figs 1-12. Structural features oftheEuropeanOrthetrum larvae: (1-2) cancellatum (L.); — (3-4)
trinacria(Sel.).; — (5)coerulescens (Fab.); — (6-7)albistylum(Sel.); - (8)nitidinerve (Sel.); —
(9-10)brunneum (Fonsc.);— (11-12)chrysostigma(Burnt.). —[Figs 1,3,6;abdomen, lateralview,
scalebar 10mm; - Fig. 2: abdomen, dorsal view,scale bar7 mm; — Figs 4-5, 7-8, 10,12:labia,
dorsalview, scalebar 3 mm; — Figs 9, 11;anal appendages,dorsal view, scalebar 1mm].
on segments 9and 10oflive larvae there isapaleareacontainedwithin thespots,labial palps
with 8 setae, length23-28 mm).
Dorsal spinesonsegments 4and5only (Fig. 3).Epiproctlengthened,ratio length/widthatleast
2,5 „ trinacria
(No abdominal spottingas above, but noticeable darkeningboth dorsally and ventrallyonlast
three segments, labial palps with5 setae(Fig.4),length 23-30 mm).
4 Labialpalps with5orless setae 5
194 S.G. Butler
Labialpalps withmorethan5 setae 6
5 Longepiproct.ratio 1/w ~ 2.Total length> 20mm ialbistylum
(Largelarva similar toO.cancellatum, but with less pronounced abdominal spotting and mid-
-dorsalclumpsofsetae,andno spines(Fig.6). Segments8.9and 10withdarkbrown suffusion
dorsally and ventrally. Labialpalps with 5setae(rarely 6) (Fig.7). length 23mm).
Shortepiproct. ratio <2. Totallength <20 mm anceps
(Closeinappearanceto O.coerulescens, butwithoutdorsalspinesand generallyalighterbrown
colourwhencleaned, labial palps with3 setae, (see alsoFig. 5).length 16-18 mm).
6 Prementum withsingle long outer setae nitidinerve
(Midbrown appearance, few markingsand littlecoloration.Labial palps with 6setae,(Fig. 8),
length 20-22 mm).
Prementumwithseveral longouter setae 7
7 Prementum with3longsetae. Total length ~ 20mm brunneum
(Variable incoloration and size.Epiproctalmostequilateralin dorsal view (Fig,9). labial palps
with6(rarely7) setae.(Fig. 10). length 18-22mm).
Prementum with 4+longsetae.Total length<20mm chrysostigma
(Mid todarkbrownincolour. Epiproctwithmore slenderisoscelid appearance (Fig. 11),labial
palps with7(rarely 8) setae.(Fig. 12), 18-19mm).
DISCUSSION
Alleight species occur in both still and running water bodies. In Europe, O.
cancellatum appears to inhabit the widest range of habitats, including lakes,
ponds, gravel pits, marshes, peat bogs, ditches, streams and slow flowing large
rivers. O. coerulescens inhabitsallbut the largerlakes andrivers. O. nitidinerve
has been recorded up to an altitude of 2300 m. (ASKEW, 1988), whilst O.
brunneum is deemeda lowland species (ROBERT, 1958). Larvae are almost
always found concealed inmud, thepresence orabsence of vegetation does not
appear to be significant. Exuviae are commonly found on vertical emergent
vegetation at the margins ofwater bodies, mostly atheights ranging from 10 -
90 cm above the ground.
MORPHOLOGICAL FEATURES
Overall length (interspecific overlaps reduce thisasa valuablefeature,
butthreemaingroupscanbediscerned). — (1)albistylum,trinacria, cancellatum:
>22mm; — (2)brunneum,chrysostigma, nitidinerve: 18-22mm; — (3) coerules-
cens, anceps: 16-20mm.
Abdomen.— Dorsal spots canbe seen in cleanspecimens ofalhistylum,
hrunneum and anceps, less so in chrysostigma and coerulescens. The boldest
marking is incancellation.Markings canbeenhanced by wetting dirty specimens
of larvae and exuviae.
Anal appendages. — Thesearenoticeably long inalhistylum,cancella-
tionandtrinacria.Theoverallshape oftheepiproct alsoseems tobeareasonable
separation feature between chrysostigma and hrunneum.
Larvalkey ofEuropean Orthetrum 195
Lateral spines. — Thesearepresenton segments8 and9inallEuropean
species, butparticularly hard to detectwithoutcare inbrunneumandnitidinerve
(cf. BELYSHEV, 1973; CONESA GARCIA, 1990).
Dorsal spines. — These are present only in cancellatum, coerulescens
andtrinacria.Inotherspecies, particularly inalbistylum andanceps,thecombina-
tionof dorsalprotuberances and clumps ofsetae give the impression ofspines
in both larvae andexuviae.Careful cleaning and observation are therefore vital
to specific identification.
Labium. — The numberand distributionoflabialsetae, although variable
in a small percentage of individuals, is most important in the separation of
hrunneumandchrysostigma andwill help toreinforceidentificationinother spe-
cies.
ACKNOWLEDGEMENTS
I am thankful to BOBKEMPand JOHN MASONforspecimens,GRAHAM VICK for advice
andcomments on thekey and toBASTIAANKIAUTA forsuggestionsandreferences.
REFERENCES
d'AGUILAR, J.. J.-L. DOMMANGET& R. PRECHAC. 1985. Guide des libellules d'Europeet
d'Afrique duNord. Delachaux & Niestle. Neuchätel - Paris.
ASKEW,R.R., 1988. The dragonfliesofEurope. HarleyBooks. Martins.
BELLMAN, H., 1987. Libellen:beobachten, bestimmen. Neumann-Neudamm, Melsungen-Berlin-
-Basel-Wien.
BELYSHEV, B.F. 1973. ThedragonfliesofSiberia (Odonata),Vol. I.pi. 1.Nauka, Novosibirsk. —
[Russ., with Engl,title].
BUTLER. S.G.,1992. Thelarva ofOrthetrum nitidinerve(Selys, 1841) (Anisoptera:Libellulidae).
Odonalologica21(1): 73-78.
BUTLER, S.G., 1992. The larva ofOrthetrum anceps (Schneider. 1845)(Odonala: Libellulidae).
Opusc. zool.flumin. 100: 1-6.
CAMMAERTS.R„ 1980.Lalarved'Orthetrumchrysostigma(Burmeister, 1839)(Anisoptera:Libel-
lulidae). Odonalologica4(2): 73-80.
CARCHINI, G., 1983. Akey totheItalianodonatelarvae. Soc.ini.odonalol. rapidComm.(Suppl.)
I; vi + 102 pp,
CLOPEAU, R„ M. LEVASSEUR & F. BOUDIER. 1987. Cld pour Lidentification des exuvies des
especes Ouest-Europeennes du genre Gomphus(Leach. 1815) (anisopteres: Gomphidae).
Martinia5; 3-12.
CONCI, C.& C. NIELSEN, 1956. Fauna d'Italia,Vol. I: Odonala. Calderini, Bologna.
CONESA GARCIA. M.A., 1990. Akey tothe Iberian Orthetrumlarvae (Anisoptera;Libellulidae).
Notul. odonalol. 3(6):86-88.
CORBET,P.S., 1953. Aterminologyfor the labium oflarval Odonata. Entomologist86: 191-196.
DUMONT, H.J., 1972. Contribution äla connaissance des Odonates du Maroc. Bull. Soc.Sei. nat.
Phys. Maroc 52(3-4)pp. 149-179.
DUMONT, H.J., 1991. Odonata ofthe Levant. Israel Acad. Sei.. Jerusalem. — [FaunaPalestina,
Insecta5J.
196 S.G. Butler
DUNKLE,S.W., 1989. SpursonOdonata legs,Selysia 18(1): 1.
FRANKE, U„ 1979. BildbestimmungsschlüsselmitteleuropäischerLibellen-Larven. Slung. Beilr.
Naturk. (A) 333: 1-17.
GARC1A-PARRON, M.J., &A. BENITEZ-DONOSO, 1988.Arecord ofthe exuviae ofOrthetrum
trinacria(Sei.)fromnorthernExtremadura, Spain(Anisoptera:Libellulidae).Nolul. odonatol.
3(2): 33-34.
GARDNER,A.E., 1954,Akey tothelarvae oftheBritishOdonata. Enl.Gaz. 5: 157-171, 193-213.
KUMAR, A., 1971. The larval stages ofOrthetrum brunneum brunneum (Fonscolombe) with a
description ofthe last instar larva ofO. taeniolatum (Schneider).J.nat.Hist. 5: 121-132.
MACNEILL, N.,The larvaofOrthetrum coerulescens (Fabricius)and itshabitat. Enl. Gaz., 19(3):
159-163.
NIELSEN, C„ 1955.Esuvia ninfaledel genre "OrthetrumNewmann”referibile probabilimenteall’
"O. nitidinerve Selys”. Boll. 1st.Enl. Unix. Bologna21: 197-200.
ROBERT,P.-A., 1958.Les libellules(odonales).Delachaux etNiestle,Neuchatel-Paris.
SCHNEIDER, W„ 1985.The types ofOrthetrum anceps(Schneider,1845) andthetaxonomic status
ofOrthetrumramburii (Selys, 1848)(Insecta;Odonata: Libellulidae).Senckenhergianahiol.
66(1/3):97-104.