The larva of Orthetrum robustum Balinsky, 1965, a localized southern African endemic (Anisoptera: Libellulidae)

4 Pages·1992·0.95 MB·English

by  Carchini, G

Odonatologica21(3):323-326 September1. 1992
SHORT COMMUNICATIONS
The larva of Orthetrumrobustum Balinsky, 1965,
a localized southern African endemic
(Anisoptera: Libellulidae)
G.Carchini ¹, M.J. Samways² and M. DiDomenico¹
1 Dipartimentodi Biologia,IIUniversity diRoma "TorVergata",
ViaOrazio Raimondo, 1-00173, Roma, Italy
2 DepartmentofZoology andEntomology,University ofNatal,
P.O. Box 375,Pietermaritzburg3200, South Africa
ReceivedFebruary20, 1992 /AcceptedMarch 27, 1992
The last instar larva isdescribed, illustrated andcomparedwiththemorphologically
similar andoccasionallysympatric O. trinacria.
INTRODUCTION
O. robustum is a libellulidrelatively recently discovered(BALINSKY, 1965)
endemic to the southern African region. It inhabits pools, swamps and slow
streams, from Natal to Zambiaand NW Botswana (PINHEY, 1985).This paper
describesthelarva and comparesthe larvalmorphology withthat ofO. trinacria
which is sympatric atsome localities.
MATERIALAND METHODS
Twomale larvae ofO.robustum,small poolsneartolake St.Lucia,Natal.South Africa,February
1990,Carchini & Samways leg.The larvae, both at the last instar, were fieldcollected andreared
in the laboratorythroughto emergence, in plastic floatingcages. Species determinations werefrom
theteneralimago.The exuviaewerestoredin 75%ethyl alcohol and thenmeasuredand drawnusing
a stereomicroscope anda cameralucida.The followingmeasurements were made: Dorsal view-
total length, anal pyramid length and width, cerci length. CORBET's(1953) terminologyfor the
labium wasused.
DESCRIPTION
Body length 25.0-25.8mm; colourdark brown, setose massive (Fig. 1). Head
324 G. Carchini, M.J.Samways & M. Di Domenico
Fig. I. Orthetrum robustum Balinsky: maleexuviae.
as typical forthegenus,withsmalleyes.Antennae7-segmented, thethirdsegment
the longest. Distance between antennae insertions shorterthan the antennae.
Mask massive, prementumclearlypointed. Twoseriesofpremental setae,each
divided in two groups, a medial one of 15-20setae, anda lateralone ofthree
more massive and longer setae. The two series are separate. The distal margin
of prementum bears 20-21 crenations interpolated with small spiniform setae
(Fig. 2). Palpus as typical for the genus, with four palpal setae. The movable
hook is not longer than the setae. The external surfaceofpalpus is rich in hair-
-like setae, the distal margin ofpalpus has 9-10 crenations, interpolated with
groupsof 2-3 small spiniform setae (Fig. 3).
Abdomenovoid, very setose,the sixthsegmentwidest. Thefirst sixabdominal
segments have dorsal spines, which are small and hiddenby the wing-sheaths
in the first three, and very stout in the following three segments (Fig. 4). The
spine ofthe fifthsegment is the largest. Lateral spines are present onthe eighth
and ninthabdominalsegments.
Anal pyramid length 3mm, width 1.9-2.0mm,with very long hair-like setae,
Larva ofOrthetrum rohustum 325
especially on the underside.Epiproct andparaprocts nearly equal in length, not
curved, and with lateral margins straight. Cerci length 1.4-1.5 mm. about half
thelength ofthe anal pyramid.
DISCUSSION
O. robustum is in general appearance very similar to O. trinacria. Both O.
trinacria andO. robustum are larger and theiranal pyramid longer than other
Orthetrum species already described, making them easily distinguishable from
other congenerics.
ThelarvalmorphologyofO. trinacriawas firstdescribedby DUMONT(1972)
from specimens from Morocco, and other informationand illustrations were
given by CARCHINI (1983) and CONESA GARCIA (1990). We compared O.
Figs 2-6. Orthetrumrobustum Balinsky (Figs 2-4) and O. trinacria (Sel.) (Figs 5-6): (2. 5) Last
instar larval mask; — (3)Last instar larval palpus; — (4, 6) Abdomenofthe exuviae, lateral view.
326 G. Carchini. M.J. Samways& M.Di Domenico
robustum with three specimens ofO. trinacria, two from Sicily and one from
Pietermaritzburg, South Africa.Theprementum is moremassive in O.robustum,
and both thepremental and the palpal setae are stouter in this species (cf. Figs
1,2, 5). O. trinacria lacks aspine onthe sixthabdominalsegment (Fig. 6). The
lateralspines on the eighth and ninthabdominal segments appear tobe smaller
inO. trinacriathanin O.robustum.TheO. trinacriaanalpyramid is longer than
in O. robustum, and thecerci proportionately shorter. Even though only two O.
robustum larvae were obtained here, the characters are sufficiently distinctive
for clear determinationofthetwo species.
ACKNOWLEDGEMENTS
We thank the University ofNatal Research Fund, the Foundation for Research Development,the
M.U.R.S.T.'PopolamentoAnimaledelMediterraneoOccidentale'. andtheItalianNationalResearch
Council (C.N.R.) for financial support. Ms PAMELASWEET kindlyprocessed the manuscript.
REFERENCES
BAL1NSKY, B.I.. 1965. Anewspecies ofOrlhetrum (Odonata)from southern Africa.Novos Taxa
ent. 39: 1-7.
CARCH1NI, G.. 1983.Odonati.Guideper ilriconoscimento dellespecieanimalidelleacqueinterne
italiane.Consig. naz.Ricerche. 21: 1-80.
CONESAGARCIA, M.A., 1990. Akey tothe Iberian Orthelrum larvae (Anisoptera:Libellulidae).
Nolul. odonalol. 3: 86-88.
CORBET. P.S., 1953. Aterminologyfor the labiumoflarval Odonata.Enlomologi.ilKo: 191-196.
DUMONT, H.H., 1972.Contributionà laconnaissance des odonates du Maroc. Bull. Soc.Sci. not.
phys. Maroc52: 149-179.
PINHEY, E.C.G., 1985.A survey ofthe dragonflies(Odonata)ofSouth Africa.Part 2.Ahisoplera,
J.ent. sth.Afr.48: 1-48.