Description and natural history of the Costa Rican Odonata larvae. 5. Megaloprepus caerulatus (Drury, 1782) (Zygoptera, Pseudostigmatidae)

7 Pages·1997·0.86 MB·English

by  Ramírez, A

Odonatologica26(1): 75-81 March I. 1997
Descriptionandnaturalhistory
oftheCosta Rican Odonatalarvae.5.
Megaloprepuscaerulatus(Drury, 1782)
(Zygoptera, Pseudostigmatidae)
A.Ramírez
InstituteofEcology, University ofGeorgia,Athens,GA 30602,United States
Received May8, 1996 /ReviewedandAcceptedAugust20, 1996
The larva is described and illustrated, and a comparisonis madewith the other
described spp. in the family. The most useful characteristic forthe separation ofthe
different spp. isthe shape ofthepalespotonthe tipofeach caudal gill.Adiscussion
ofthe morphologicalsimilarities ofthe phytotelmatadwellersispresented and it is
notedthat spp. ofZygopteraaremore similartooneanotherand share morespecial-
izedcharacteristics thantheAnisopteraspp. Also,the larvae ofthe Pseudostigmatidae
are very similartothose ofCoenagrionidaethat breed inphytotelmata,the main dif-
ferences beingbody size andnumber and shapeoflabial palpiteeth.
INTRODUCTION
The family Pseudostigmatidae has been a subject of research since early
odonatologists foundadults flying inthe forest farfrom any typical or obvious
larvalhabitat.Whilereseachers wereabletocollectandstudytheadults, thelarval
habitatremainedunknownformanyyears. DrD.C. Geijskes wasoneofthefirstto
try to find the microhabitatof the larvae, particularly that of Megaloprepus
caerulatus.Themostlikely habitatatthattimewas thoughttobetank bromeliads
(CALVERT, 1923),and itwas not untilthe 1985S.I.O. Symposium inParis, that
GeijskeslearnedfromO.M.Fincke thatthelarvaeare tree holedwellers.Itwas his
wishto describethelarvaebuthis untimely deathmadethis impossible. I, there-
fore,dedicatethismodestpapertothememoryof DrD.C. G eijs k es, though it
cannot becompared withwhathewould havedone.
Severalinteresting papershavebeenpublished on theecology and taxonomyof
the family Pseudostigmatidae (CALVERT, 1911, 1923;FINCKE, 1984, 1992).
However, the larval taxonomy developed slowly, mainly because the specific
76 A.Ramirez
microhabitatmakesthecollectionofspecimens difficult.
The family has six species in Central America, split among three genera
(PAULSON, 1982). Thereare four knownspecies; Mecistogaster modesta (Sel.)
(CALVERT, 1911),M. ornata Ramb.(RAMIREZ, 1995),Pseudostigma aberrans
Sel. (NOVELO-GUTIERREZ, 1993) and Megaloprepus caerulatus (Dru.).
NOVELO-GUTIERREZ (1993) statedthatthelarvae ofatleasttwo more species
havebeenreared forecological studies, butformaldescription arestill tobe com-
pleted.
Previousto the present study, Megaloprepus caerulatuslarvae were separated
fromotherspecies usingcharactersprovided by earlierecological studies(FINCKE,
1984, 1992;DELA ROSA & RAMIREZ, 1995). Forexample, FINCKE (1992)
briefly described how to separate several species ofthe family, amongthem M.
caerulatus.
Thelarvaeusedforthepresentstudy werefoundliving insmallwater bodiesin
tree holes.Almostallofthetree holeshadacapacity ofnearly oneliterand were
situatedatdifferentheights above theforest floor.
Also foundwith the larvae were larvae of M. ornata, (Pseudostigmatidae),
Orthemisferruginea (Fab.) (Libellulidae)aswellaschironomidsandotherdipterans.
MEGALOPREPUSCAERULATUS (DRURY, 1782)
Figures 1-6
Material. - 2exuviae (6,9) ofspecimensemergedin laboratory,2 larvae(<J, 9), lastinstar,
2intermediate instars, Maritza Biological Station,Guanacaste Conservation Area,Guanacaste prov-
ince,24-1-1994, A.Ramirez,N.Barbee&C. delaRosa, leg.;- 2larvae (3, 9), lastinstar,collected
in 1986;- 3 exuviae (<J, 9), last instar, 27-XI-1982 & 2-XI1-1982. 6 larvae, (<5, 9), intermediate
instars, 11-1986. Barro Colorado BiologicalStation,Panama, O.M.Fincke leg.
DESCRIPTION. - Larvaeand exuviaelight brown or brown; body slender and
long, almostentirely glabrous, withseveral distinctivepale areas, asfollows:three
whitespots on themid-dorsalfaceofthethorax,two behindthespiracles andone
inthemiddle,betweenthespiracles (Fig. 1).Oneconspicuous whitespot atthetip
ofeach caudalgill.
Head.-Widerthanlong,occiput smallandconcave, cephaliclobespronounced
and rounded, withgroupsofspiniform setae; labrumwith two pale lines ateach
sideofthemidline,slightly converging inthemiddle,indorsalview;clypeusbrown
with atriangularmiddorsalpale area, justinfrontofthelineson labrum.Antennae
7-jointed, as long as thehead,glabrous or with fewscattered setaejust proximad
thearticulations; uniformly colored;proportion ofantennomeres,frombase totip:
0.37, 0.51, 1.0, 0.67,0.45, 0.30, 0.15. Mandibles biramous,external branch with
fourteeth, theventralone witha smalltoothatits base, internalbranchwithtwo
teeth. Galeolaciniaewith four, robust andslightly curved teeth,similarin length
and arranged ina row, with scattered setae throughout; maxillary palpi covered
LarvaofMegaloprepuscaerulatus 77
withnumerouslong setae.Labiumlightbrown,prementum-postmentumarticula-
tionreaching the proximal margin ofthe mesocoxae; prementumglabrous, but
with arow of small spines on the apical 0.25 (Fig. 4); ligula prominent with the
margin serrated. Palpal setae 6-7, basal 0.7ofexternal margin withsmall setae,
internal margin smooth; two palpal teethofsimilar shape (Fig. 5).
Thorax.-Pronotumglabrous, posterolateral angles rounded, frontalmargin
bilobed, lateral margins with long setae; posterior margin with threedistinctive
pale areas, onebehindeach spiracle and anotherinthe midline.Synthorax with
Figs 1-6. Larval morphologyofMegaloprepuscaerulatus: (1)female, last instar, generaldorsal as-
pect;- (2)femalegonapophyses,lateralview;- (3)caudalgill,lateral view;- (4)prementum, dorsal
view;—(5)labialpalpi, dorsalview; - (6)female cercus,lateral view.
78 A.Ramirez
some mediumsize setae on the lateral margins, a pale area along the anterior
middorsal line. Hind pair of wing sheaths reaching the posterior margin of ab-
dominalsegment5, thefront pairreaching the0.5ofthesamesegment.Legs light
brown, femorawith 2rows of dorsal, 2 ofventral and one lateralsmall spines;
tibiaewith2 ventralrowsofsmallspines andsomescattered dorsalsetae,distal0.2
with a densegroupofsmallspines, nearthearticulationwiththetarsus;tarsus 3-
-jointed withtworows ofventralspinesandlongsetae onthedorsalside.Pulviliform
empodium presentontarsus.
Abdomen.- Uniformly lightbrown, darkernextto theposteriormargins of
eachsegment,completely glabrous, butposteriormargin ofsegment10witharow
of small setae; withouteitherdorsal protuberances, or lateral spines. Female
gonapophyses reaching the basal 0.6 ofsegment 10, external lobes ending in a
roundedtip with asmall spine, theinner onesshorter than theexternals (Fig. 2).
Male gonapophyses cone shaped, ending acutely and not reaching the posterior
marginofsegment9.Maleandfemalecercismallandconical(Fig.6). Caudalgills
flattened(Fig. 3),slightly longer thanwide,darkbrownandharderintexture inthe
basal0.25,therest graycolored with violetanda softertexture nearthe borders;
witha distinctivepale area atthetip ofeachone.
Measurements (inmm). - Total length (excluding gills)22, abdomen 15,lateral gills 4,
medial gill4,metafemur5;- head: width 5,length3;- prementum: width 3,length5.
variation. - Somespecimens hadamodifiedtarsus onthefrontor middlelegs;
they were 2-jointed andoneoftheclaws was larger thantheother.
DISCUSSION
AllPseudostigmatidae larvaeare characterizedby being adapted to liveinvery
similarandsometimesidenticalmicrohabitats.Forexample,fourofthesix species
ofthe family in Central America have been found living in tree holes and it is
known thatthreeor morespecies areableto livetogether inthesametree holeat
thesametime(FINCKE, 1992;DELAROSA& RAMIREZ, 1995).Thissuggests
thatdifferentgenerawere subjecttosimilarselectionpressures, probably resulting
inthemorphological similarity observed amonglarvaeofthePseudostigmatidae.
Theshape andstructureofthecaudal gillsare themostusefulcharactertosepa-
rate thegenera;they arebasically leaf-like,but vary insizeandshape. Thefactthat
two genera.Pseudostigma and Megaloprepus, havepale areas atthetip moreevi-
dentin thelatter, makes genusidentificationeasier.Allknown species ofPseudo-
stigmatidae larvaecanbeseparated using thekey in RAMIREZ(1995).
THE PHYTOTELMATADWELLERS
Among Odonataitis not uncommonto findspecies withlarvaethatliveintree
holes,bromeliadsor similarhabitats,generally knownas phytotelmata (CORBET,
Larva ofMegaloprepuscaerulalus 79
1983).Someofthesespecies areopportunistic as is thecase inseveralAnisoptera
species such asOrthemisferruginea andLibellulaherculea(pers. observ.). Others,
however,seem tospecialize in thiskindofhabitat, forexample all species inthe
familyPseudostigmatidae andthecoenagrionid genusLeptagrion.
Fromaliteraturereviewitisevidentthatanisopteran larvaelivinginphytotelmata
do not show special morphological adaptations and that larvae are morphologi-
callyidenticaltothosethatliveinothertypesofhabitats(e.g. pools). Severalspe-
cies of Aeshnidae, such as Indaeschna grubaueri (Forster) (ORR, 1994), and
Gynacantha membranalisKarsch (SANTOS et al., 1987;FINCKE, 1984), have
beenfound living in phytotelmata andin pools on theground, withoutany mor-
phological characteristicsthatcouldindicateanadaptationtoanyofthesehabitats,
besides differentcolor patterns, whichare known to vary with the color ofthe
microhabitat(CORBET, 1960;RAMIREZ, 1994).
ThecaseofZygoptera larvaeiscompletely different.Larvaeofdifferentfamilies
andgenerathatdwell inphytotelmata tendtobemoresimilaramong themselves,
sharingmanymorphological characteristics.Theseincludemodifiedleaf-likegills
(Fig. 3)usually coloredblack andpurple,glabrous bodies, darkcolorpattern,short
labiumwith triangular prementum, shortlegs, and labialpalpus with 4-5 setae.
Phytotelmata dwellers tend to be larger than related species that do not use this
habitat(ORR, 1994).LarvaeofthefamilyPseudostigmatidae andCoenagrionidae
are ingeneral verydifferent, butwhenlarvaeoftheformerarecompared with the
species ofthelatterthatbreedinphytotelmata, thedifferencesarelessevident.DE
MARMELS (1985)described thelarvaeof Leptagrion fernandezianum Racenis
whichliveinbromeliads.Fromhis descriptions andcommentstheresemblanceof
thespecies toMecistogasterisclear.ORR(1994)describedthelarvaeofPericnemis
triangularis Laidlaw(Coenagrionidae). This species also shows all the morpho-
logical characteristics ofthe phytotelmata dwellers(see above). Finally, another
bromeliaddwellerisDiceratobasismacrogaster(Sel.) (Coenagrionidae) (WEST-
FALL, 1976).Inthis case thelarvais similartotheotherspecies describedabove
only differing in the shape of the caudal gills, which are more typical of
Coenagrionidae. Morphologically, D.macrogasterrepresentsanintermediatestep
betweenthenormalCoenagrionidae andthephytotelmata dwellers.
Inconclusion,phytotelmata-dwelling species ofCoenagrionidae andallspecies
ofPseudostigmatidae are morphologically similar.Thedifferencesare mainly the
size andshape ofthelabialpalpi, thedisposition ofthepremental setae, andin a
few cases, shape ofthe caudal gills. Pseudostigmatidae lack thepremental setae
andthelabialpalpi havetwo endteeth(Fig. 5).However,thesecharacteristicsare
variable among the phytotelmata-dwelling Coenagrionidae. For example, P.
triangularis lacks the premental setae but itslabialpalpi are modified, with one
endhook andaserrated area. Thelabialpalpi ofL.fernandezianum is similar to
thoseofPseudostigmatidae butithaspremental setae.Thelength ofthefinalinstar
inPseudostigmatidae is notless than 18mm, whileinCoenagrionidae itis usually
80 A.Ramirez
not morethan 18 mm.
SANTOS (1966) and DE MARMELS (1985) concluded that the Pseudo-
stigmatidaeevolvedfrom theCoenagrionidae. This conclusionissupported by the
present study. In orderto improve our understanding ofthis relationship more
Coenagrionidae larvaeneed tobereared and described.
ACKNOWLEDGEMENTS
Iam verygratefultoDr C.DELA ROSAforhishelpcollectingthematerial, toDr P,CORBET for
kindly givingmethehonor ofdescribingthelarvae, tohim and DrO.M.FINCKEforallowingmeto
studytheirspecimens, and toDrP. HANSON, DrP.CorbetandJ.P. BENSTEADfortheircomments
onthemanuscript.
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