Description of the last instar larva of Orthetrum hintzi Schmidt, 1951, and comparison with other African Orthetrum species (Anisoptera: Libellulidae)

5 Pages·1996·1.2 MB·English

by  Carchini, G

Odonatolugica25(1): 73-77 March I, 1996
SHORT COMMUNICATIONS
Description of the last instar larva
of Orthetrum hintzi Schmidt, 1951,
and comparison with other
African Orthetrumspecies
(Anisoptera: Libellulidae)
G.Carchini and M. Di Domenico
Dipartimentodi Biologia,Universita “Tor Vergata”,
Via della Ricerca Scientifica, I-00133 Roma, Italy
Received May 16, 1995 /Revised and AcceptedOctober 12, 1995
The ultimate instar larva is described and illustrated from specimens collected
in the streams nr York, Sierra Leone, Itis the smallest ofthe known Orthetrum
larvae, fromwhich itcan be separated by the presence ofdorsal abdominal spines
onS7. The mainlarval featuresin8 African Orthetrum spp. are brieflyreviewed.
INTRODUCTION
Orthetrumhintziis a widespread libellulid, inhabiting the warmer portions of
the bushand forest streams, from Natal to Transvaal, up toE andW equatorial
Africa(PINHEY,1985).Inthepresentpaper,thelarvaisdescribedforthefirsttime.
Acomparison is also made withthe larvalmorphology oftheother hithertode-
scribedAfricancongeners.
MATERIAL AND METHODS
Five last instar larvae were collected in the streams near York, Freetown Peninsula, Sierra
Leone, 9-III-1992 (W. Rossi leg.). They were reared in plastic floatingcagesthrough to emer-
gence inthe laboratory. Species identification is based on theteneralimago.
The exuviae were stored in 75% ethyl alcoholand then measured and drawn,using a stereo-
microscopeand acameralucida. The (dorsal view)measurements aregivenin Table I.CORBET’s
(1953) terminology for the labium was adopted.
74 G. Carchini & M. Di Domenico
DESCRIPTION
Body sizesmall, colourbrown,poorlysetose (Fig. 1).Headtypical ofthegenus,
withsmalleyes. Tuftsoflong hair-likesetae behindandbetweentheeyes,on the
antennae and between their
insertions(Fig. 2a).Antennae
7-segmented, the third seg-
ment the longest. Distance
between antennae insertions
shorter than the antennae
length. Maskquadrate,nearly
as long as wide.Twoseriesof
premental setae, each di-
vided intotwo groups,ame-
dialoneof 15-20smallsetae,
and a lateral one of 3 long
setae.Eachseriesforms anS-
-shaped pattern. The distal
margin of prementum is
clearly pointed, with 12-15
crenations interpolated with
stout and sharp spiniform
setae (Fig. 2b). Palpus typi-
calofthegenus,with5 palpal
setae. The moveablehook is Fig. 1. Orthetrum hintzi Schmidt, last instar larva (total
thin and shorter than the length 15.5 mm).
setae.Thedistalmarginofpalpushas 10-15crenationsinterpolatedwithgroupsof
2-4spiniformsetae(Figs 2c, 2d).Legsrobustand setose.Abdomenovoid,not very
setose,thefifthsegmentwid-
Table I est.ThesegmentsS4-S7have
Sizeranges (in mm)ofsome morphologicalfeatures from long dorsal spines with
five individuals of Orthetrum hintzi larvae' rounded apex, almost equal
insize(Fig.2e).Lateralspines
Total length 14.8 - 15.6
Head width 3.7 - 4.0 on segments S8-S9. Two se-
Distance between antennae insertions 1.5 ries of pale spots laterally
Antennae length 2.2 - 2.3 along thedorsalkeel onseg-
Prementum length,lateral view ',3.2 - 4.0 ments S6-S9 (Fig. 1). Anal
Anal pyramid length 1.2
pyramid short, setose, about
Anal pyramid width 1.2 - 1.3
Cerci length,lateral view 0.5 - 0.7 as long as length ofS9 and
Epiproctum length, lateral view 1.1 - 1.2 S10. Epiproct slightly longer
Paraprocta length,lateral view 0.9 - 11 than paraprocts. Cerci about
Metatibia length 4.0 - 4.5 halfofthe length oftheanal
Larva of Orlhetrumhinlzi 75
pyramid. Formeasurements seeTableI.
DISCUSSION
Thereare23Orthetrumspecies recordedto dateasoccurringinAfrica(DAVIES
& TOBIN, 1985).Thelarvalmorphology ofmostofthemis stillunknown,except
for8 species: O.brachiale(P.deBeauv.),describedby PINHEY(1961), O. caffrum
(Burn.)by PINHEY (1959),O. chrysostigma (Burm.)byCAMMAERTS(1975),O.
juliaLongfield by BARNARD (1937)as O. capenseCalv., O. nitidinerve(Sel.) by
CONESAGARCIA(1990),O. robustumBalinsky byCARCHINI etal.(1992),O.
trinacria Sel. by
DUMONT(1973) and
CARCHINI (1983),
and O. hintzi(present
paper).
O. hintzi is the
smallest of the de-
scribedOrthetrum.For
this reason, it resem-
bfes O. brachiale,
which is just a little
bigger, but this latter
species is completely
lacking any dorsal or
lateral spines on the
abdomen.Ontheother
hand, O. hintzi bears
long, rounded dorsal
spines on segments
S4-S7.Itcaneasilybe
separated, since no
other species has dor-
sal spines or keel on
S7.As tothe premen-
talandpalpal features,
itisnot differentfrom
theotherspecies ofthe
genus.Thebody ofO.
hintziappearsscarcely
setose,withrespect to Fig. 2. Orthetrum hintzi Schmidt, larval structural features: (a) head,
frontal view (width 4.0mm); - (b) mask, dorsal view (length 3.5
theother species, ex- mm, width 3.5 mm); - (c) palpus; - (d) same, detail of distal
ceptforhead,legs and margin;- (e) abdomen, lateral view.
76 G. Carchini & M. Di Domenico
analpyramid. This is unusual inthegenus.Mostifitsmembers liveinthemudof
still or slowly running waters, so thatthesetae on the body, retaining abig quan-
tityofdebris,concealthelarvaefrom predators. Unfortunately, we haveno dataon
theecology or habitatofO. hintzi, thereforeitis not possible atpresenttoexplain
the scarcity ofsetaeonits body.
As the larvae ofonly afew species have been described, it is not possible to
proposeanidentificationkey fortheAfricantaxa.However,someusefulcharacters
can be highlighted.
Thebody sizeis variable,ranging from 15mm(O. hintzi)to27mm(O. trinacria),
butthelarvalmorphology isoverallratheruniform.Themorphology ofprementum
andpalpus is quiteconstant, though thereare differencesinnumberandposition
of premental and palpal setae. All the species show two symmetrical series of
premental setae. Eachseriesis composed ofafewlong, lateralsetae andagroupof
10-20or moreshorter setae. In O. chrystostigma, thelong andshortsetae are not
clearlydistinct, becausethesetae becomegradually shortertowardsthemiddleof
prementum. O. nitidinerve is immediately distinguishable in having only one
long premental seta, whilethereare2-4in all theotherspecies.
Theepiproct andparaproctshapeisalsosimilarinalltheOrthetrumspecies. The
analpyramid is aslong as,oralittlelonger than,S9andS10.Only O. trinacriahas
a very long analpyramid, clearly longer than S9andS10.
The numberandsize oftheabdominal spines can beused to dividethegenus
intospecies groups.In fact, O. chrysostigma, O. brachialeand O. nitidinervedo
not have any spines or keel on themediallineoftheabdomen.Theother species
bearmoreor less stoutspines, but sometimesonly aslight dorsalspine ispresent
(O. caffrum, O.julia).Thelateralspines canalsobetotallyabsent,asinO.brachiale,
O. chrysostigma andO. caffrum. In theotherspecies, they arepresent, although in
some species they are hardly detectablebecause they are coated with hair-like
setae.
ACKNOWLEDGEMENTS
We wish to thank Professor WALTER ROSSIwho kindly sent usthe material described here,
and Professor SALVATORE CARPI forthe identification ofthe adults. The study was financed
by grants fromthe ItalianM.U.R.S.T.to GianmariaCarchini (programma“PopolamentoAnimale
del Mediterraneo Occidentale”) and by Accademia Nazionale dei Lincei.
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