Morphological variations in relation to maturation in Pantala flavescens (Fabricius) in central Japan (Anisoptera: Libellulidae)

2007·2.7 MB·English

by  Ishizawa, N

Odonalologica36(2):147-157 JuneI.2007
Morphologicalvariations inrelation
to maturationinPantala flavescens (Fabricius)
incentral Japan
(Anisoptera: Libellulidae)
N.Ishizawa
1644-15Yamaguchi,Tokorozawa City,SaitamaPref.,359-1145,Japan
[email protected]
ReceivedFebruary24,2006/ RevisedandAcceptedSeptember6,2006
P.flavescens wasinvestigatedin openfields in adeciduous forest in aninland
partoftheKanto regionfor 3months fromlate June2003. The sp.was estimated
tobebivoltine from summertolate autumn.Thesizeoftheadults wasunchanged
throughouttheseason.Thesexratioofthepopulationskewedtowards 9.Maturity
degree(MD),shownasthevalue ofbodyweightdivided bythecubeofwinglength,
shifted upwardsuntil thesecond halfofAugust,afterwhichitdecreased sharply.
Similarlythewingloading(WL)(calculatedbydividingbodyweightbywingarea)
increased until the second half of August,and decreased fromSeptember,and
in early October itwas not significantlydifferent between S3 and 9$. Asthe
relationship of body temperatureto ambient temperatureshowed no difference
betweenmature andimmature individuals,orbetween sexes,with bothcorrelation
coefficients andregressioncoefficients beinglargeforaflyertypesp., theyseemed
tobeeasily affectedbythe ambienttemperature.
INTRODUCTION
Pantalaflavescens is the most common dragonfly onthe earthandis famous
for its migratorybehaviour. InJapan it appearsinmass swarms in thehot sea-
son of Bon Festivalinsummer, andis calledbon-tomboorshoryo tombo.This
dragonfly flies over the ocean from the South, and its migration has beenob-
served fromaweathership (ASAHINA &TSURUOKA, 1967;HASHIMOTO
& ASAHINA, 1969).ISHIDA (1989) observedthespecies flying fromover the
ocean atTobaCity inMiePrefecture, andWAKANA(1959) describedprecisely
his observationsoflarge swarms in early autumn. Itis saidthatcoming over to
the mainlandof Japan itgoes Northby repeated alterationof generations and
148 N. Ishizawa
thatits eggsand larvaecannot overwinteronthemainland.Hencethey are ex-
tinctthere as abreedingpopulation (ISHIDA etal., 1989).
Although manyreportson migrationandforaging ofthisspecies havebeenmade,
the seasonalchanges ofthe degreeof maturity,wing loading, thermoregulation
and seasonalchanges of maturity in the species havescarcely receivedany at-
tention.Thisstudy was madeto clarifythe morphological variationsin relation
to maturationofthe species coming overtoopen fieldsin aforest far fromthe
water areas.
STUDY SITESAND METHODS
Studiesweremade fromlate JunetoOctoberin 2003 atKunugiyamaforest(ca 152ha,35°50’N,
139°28’E,60ma.s.1.)ontheborders ofthreecities andatown,Tokorozawa,Sayama, Kawagoeand
Miyoshi,which arelocatedontheMusashino lowland hillsin thewesternSaitama Prefecture.Asthe
inland forestislocated morethan 1km fromthenearestwaterbodies,the specimenscollected there
mightberegardedasmigrantsfromotherregions.Supplementaryinvestigationsweremadeinearly
SeptemberattheKabazaka Pass (810ma.s.1.)intheOkumusashi Hills,westernSaitamaPrefecture,
and in late JulyatHino (680m a.s.1.),Nagasaka-cho,Kitakoma-gun,Yamanashi Prefecture,about
90km West ofKunugiyamaforest.
Size and body weightweremeasured within six hours ofcapture.The hindwingwasused asa
measureofsize,usingaslide caliper,and thebody weight(exceptinthespecimens fromNagasaka-
cho)wasmeasured with anelectronicbalance to0.001 g.
Degreeofmaturity(MD)wascalculatedbydividingthebodyweightbythecube ofthehindwing
length,and this alsogivesthe specificgravityofaspecimen.Thevolume ofanadultisunchanged
throughoutitslifeand,asitmatures, itsweightincreases. Accordingly, theweightdividedbythevol-
ume,i.e. the specificgravity,mayberegardedasdegreeofmaturity.Thisvalue wasused effectively
forSympetrumfrequensbyISHIZAWA(2004,2005),
Wingloading(WL)wascalculated asfollows; fromthecapturedindividuals amaleandafemale,
ofbodyweights340mgand431 mg,respectively wereselected asstandards.Theirwingswerephoto-
copied.Usinganimagesizeof200%,thewingshapes ofthephotocopieswerecutoutandweighed.
Theratio ofthe weightofeachofthese shapestothe weightofa 100cm2cut outwascalculated.
This gaveavalue of 16.3cm2 forthe maleand 18.8cm2forthe female,and thesewereregardedas
thestandardwingareas(STWA).Wingareasofotherspecimenswerecalculated asfollows:STWA
(cm2)x thesquare(cm2)ofeach hindwinglength- thesquare(cm2)ofthestandardhindwinglength.
TheneachWLwascalculated bydividingthebodyweight(mg)bythisvalue(cm2).
Theabove data onWLwerecomparedwith those ofOrthetrumalbistylumspeciosum,collected at
OmoripondatIrumaCity,Saitama Prefecture in2000 and2001,and werealmost thesamesize as
P.flavescens.
Asanindex ofmaturityI examined how fartheabdominal segmentswerepruinescentfrom the
3rd segmentbackwards, and defined the number ofthe lastpruinescentsegmentasthedegreeof
pruinescense(PD).Incaseswherehalfofthelastsegmentwaspruinescent,theimmediatelyanterior
segmentnumber + 0.5 wasused asthePD.
Bodytemperatures(Tb) oftheindividuals weremeasured by thesamemethod appliedformeas-
uringthebody temperaturesofS.frequens(ISHIZAWA,1998a);Tbweremeasured to0.1°Cwith a
HoskinsF-V-K-002thermocouple(diameter0.05mm)setinahypodermicneedle(externaldiameter
0.3ram),whichwasinsulated withpaper covering, andconnected toaJohn-Fluke 55double-chan-
neled digitalthermometer. Themeasurementsweremadewithin about 10secondsafternettingthe
dragonflies,byinsertingtheprobethroughthemesh ofthenettothecenterofthethorax, 1mm up
Morphologicalvariationsin Pantalaflavescens 149
themesothoracic spiracle.Ambient temperaturesataheightof 1m in the sun(Ta)weremeasured
with anOmronHC-100thermistorsoonafterthemeasurementsofTb.
Toinvestigatethedifferenceofthermoregulationamongindividuals inrelation toMD,I dividedthe
dragonfliesintotwogroups (regardlessoftheseason)ineachsexbyusingthe standardsofMD4.8
in the male and MD 5.4inthe female. Those lessthan thestandards werecalled immature;those
abovethem werecalledmature.
Data ofcoefficients ofother Odonata in Figure4wereobtained fromAnaxjuniusfromMAY
(1976),A.parthenopejulius(Ishizawa,unpublished),A.guttatus(ISH1ZAWA,1998b),Anotogaster
sieboldii (ISHIZAWA,2003), patrollingCordulia aeneaamurensis (Ishizawa,unpublished),Mnais
costalis oforange wingtype(ISHIZAWA,2000),Orthetrumj.japonicum(Ishizawa,unpublished),
O.albistylumspeciosum(Ishizawa,unpublished)and bothsexesofS.frequensduringthereproduc-
tiveperiod(ISHIZAWA,1998a).The sexormaturityofA.juniuswasunknown. Dataonall other
speciesexcept S.frequenswerefrommaturemales.
Data ofthesize,body weight,MDand WL weretested usingat-test;sexratios weretestedus-
ingthechi-squaretest.Tb and Taamonggroups ofthesexesorimmature andmature groupswere
tested usingthe ANOVA-testandt-test.Correlation coefficientsofeachgroupwerecomparedusing
thez-test.
RESULTS
Thefirstrecordintheforestwas on26thJune2003, whensix individualswere
sighted flyingaroundover anopenfield; thelastrecordwas on20thOctober.
Figure 1showsthechange ofthesex ratioofcapturedspecimens. Throughout
theinvestigation periodthesexratiowassignificantly skewedtowardsthefemales
(67.3%, P <0.05)except thatofthe specimens captured in lateJuly at Nagasa-
ka-cho, which were skewed
towardsthe males(73.3%, P
<0.05,n= 11).
Hindwinglength wasca40
mmandnotnoticeablydiffer-
entbetweensexesthroughout
theseason;40.2±1.2mm,n=
53in the maleand 40.6±1.5
mm, n = 109 in the female,
respectively (P > 0.05; Tab.
I).Comparing theearly sea-
son (before September) and
thelateseason(fromSeptem-
beronwards), thedifference
in length was not significant
(P=0.46); inthemalesit was
40.4±1.1mm(n= 26) in the
early season and 39.9±1.2
mm(n=27)inthelateseason Fig. 1.Sexratios ofPantalaflavescenscapturedat surveyed
(P>0.05),although malesdo areas.
150 N.Ishizawa
have apropensity to become smaller. Inthe females the size was 40.6±1,2mm
(n = 60) in theearly seasonand40.7±1.8mm(n =49) inthelateseasonandthe
differencewas not significant, althoughthe s.d. tendedtoincreaseinthe latter.
Body weight ofthe malesincreasedfromthesecondhalfof July(332.6±51.1
mg,n= 19),andafterreaching apeak (401.0±18.0 mg,n=2)in thesecondhalf
of August, it reached itslowestlevelin October(Tab. I).In late September one
ratherheavy individual(398 mg)was captured, though mostof thoserecorded
in thelateseason werelight(ca 200mg).InearlySeptember oneimmatureindi-
vidualof 159mginweightwas captured. Thedifferenceinweight betweenboth
seasonswas significant (P <0.001).
Inthe females, body weight was sustainedatalevelof ca400mg untilthesec-
ondhalfof August, whenit reached apeak of 446.8±53.8mg (n = 6).Itthen
decreasedrapidly by 100 mg,reaching its lowestlevelof ca200mgin October.
Thedifferencein thebody weight between the seasons was significant as inthe
males(P <0.001). Theheaviestfemalespecimen (537 mg)was captured on July
16andonecaptured onSeptember28 weighed 533mg.Thesecondwas theonly
onethatexceeded 500mgin thelate season. Thebody weights ofboth sexes in
the second halfof October (228.0±37.5 mg, n= 3 in the maleand 246.7±37.0
mg,n= 15inthe female)weresimilartothosefromtheKabazakaPasscaptured
inearly September.
Table I
MorphometricdataofPantalaflavescenscapturedatKunugiyamaforestand KabazakaPass- [Hind-
wing:mm, Bodyweight:mg, Wingloading(WL): mg/(cm-cm). - Abbreviations: s: second,f:
firsthalf,MD; maturity(thedivision ofthebodyweightbythe cubeofthehindwinglength),PD:
pruinescens(thelastpruinescentsegmentnumber,and incaseofhalfofthe lastsegmentwaspru-
inescent,the immediatelyanteriorsegmentNo.+0.5 was definedasPD). Firstline ofvalues males,
secondfemales. Meanvalueswith standard deviation]
Julys. Aug.f. Aug.s. Sept.f. Sept.s. Oct.f. KabazakaPass
Number 19 4 2 13 n 3 4
36 17 6 23 12 15 7
Hindwing 40.4+1.1 40.511.0 39.410.8 39.910.8 40.411.1 38.311.6 40.210.6
40.5±1.1 40.611.3 40.811.1 40.811.1 40.213.1 40.911.2 40.911.0
Body
weight 332.6±51.1 358.8120.5 401.0118.0 263.8151.5 321.8145.6 228.0137.5 230.8157.5
395.0±84,5 437.2147.5 446.8153.8 323.7175.4 339.91110.7 246.7137.0 262.4133.7
MD 5.0±0.7 5.410.2 6.610.7 4.210.9 4.911.0 4.111.0 3.610.8
6.011.2 6.510.4 6.610.8 4.811.1 5,211.5 3.610.5 3.810.5
WL 19.812.7 21.310.8 25.412.1 16.213.3 19.413.3 15.313.1 13.913.4
23.014.7 25.011.8 25.613.0 18.514.3 19.615.7 14.011.8 14.912.0
(range) (25.9-12.0) (22.3-20.5) (27.5-23.3) (20.9-9.4) (27.4-15.4) (18.9-11.4) (18.7-9.4)
(29.4-13.7) (28.7-21.6) (30.5-21.0) (25.8-10.7) (28.0-9.1) (17.3-11.3) (17.2-10.9)
PD 5.111.3 5.310.7 5.810.4 5.810.5
(n=19) (n=16) (n=6) (n=13)
Morphologicalvariations inPantalaflavescens 151
As the hindwing length was unchanged throughout theseasonand the body
weightdifferedbeforeand afterthe beginning ofSeptember, MDsynchronized
naturallywiththevariationsinthebody weight. ThemeanMDwas4.8±1.0(range
2.4-7.4) inthemalesand5.4±1.4(range 2.4-8.0) inthefemales, respectively. The
MDofbothsexes increased untilthe secondhalfof August, butdecreasedsig-
nificantlyfromSeptember onwards,although a smallpeak appeared inthesec-
ondhalfofSeptember (Tab. I, 6: P= 0.00753 9: P= 2.664E-10). Therangeof
MDwas 2.4-7.4 inthemales and2.4-8.0inthefemales, respectively. Regarding
theindividualsofwhichMDexceededthemeanvalueas sexually mature adults,
thesharerate oftheseintheearlyseasonandinthelateseasonwas80.8%:14.8%
inthe malesand 82.8%:28.6%in thefemales, respectively.
Onlyonemalewithared abdominaldorsumwas captured during theseason,
and ithada MDof7.3. One femalewithamature ovary (found by dissection)
hadaMDof4.7,allotherswithamature ovaryfallingintherange5.4-7.4.Prob-
ablytheindividualwithaMD of4.7mighthavepreviously oviposited.
Theaveragewing loading(WL)ofthe maleswas 18.8±3.6mg/cm2, (range of
9.4-27.5mg/cm2 n = 53), andthatofthe females was 20.8±5.5mg/cm2 (range
, ,
9.1-30.5mg/cm2-n= 107)foralltheseasons. ThedifferenceofWLbetweenthe
Fig.23Dgraphofwingloadingsby periodin Pantalaflavescensfemales capturedatKunugiyama
forestfromthesecondhalfof Julytothefirst halfof Octoberin2003.
152 N. Ishizawa
sexes was significant (p <0.01). TheaverageWLofthemaleswas20.4±2.9; mg/
cm2(n =26) intheearlyseason, and 17.413.6; mg/cm2(n =27),inthelateseason,
asignificant difference(P < 0.001). ThedifferenceofWLbetween the seasons
was also significant inthefemales(23.614.3; mg/cm2,n=58,intheearly season
and 17.414.7;mg/cm2 n= 49,inthelateseason) (P<0.001). Inthe secondhalf
,
of July morethan two thirdsof femalesexceeded aWLof20 mg/cm2 andWL
was sustained untilthe second halfof August.
Figure 2 shows a 3D histogram oftheWLofthefemalescaptured at Kunigi-
yama forest.Itindicates thatmature individualswith high WLexceeded imma-
ture ones intheearly season, andas the season advanced, immatureindividuals
outnumberedthe mature ones.
As femalesmature,most of them pruinosed on the ventral sideof theirab-
domensfromthe 3rdsegment backwards. The degreeofpruinescens (PD)rose
from5.111.3in thesecondhalfofJuly,toreacha peak of5.810.4inthesecond
halfof August. Itremained atthis level(5.810.5) into the first halfof Septem-
ber, butthereafternopruinescent individualwascaptured. However,therewere
examples whereanindividualof533mginweight wasnot pruinescent, whereas
oneofonly330mginweight was pruinescent,(PD 5.5).Therewasnosignificant
correlationbetweenPDandbody weight(r= 0.140,P>0.3) orbetweenPDand
MD(r=0.094, P> 0.5).
Figures 3Aand3B showtherelationships ofbody temperature(Tb)to theam-
bienttemperature(Ta) ineach sex ofmature andimmatureindividuals.Thecor-
relationcoefficientandthe regression coefficientofimmaturemales were0.906
Fig. 3.Thecorrelation betweenbody temperatureand ambienttemperature inthe male(A) and in
the female(B),respectively. Asolid andopentriangleshow animmature male and amaturemale,
respectively, and asolid and opencircle showanimmature female andmaturefemale,respectively.
Allofthedata werecollected atKunugiyama forestfromJulytoOctober 2003.Equationsare:im-
maturemale,Tb= 1.085*Ta+ 3.676,r=0.906(n=7);maturemale,Tb=0.757*Ta + 14.021,r=
0.885 (n= 15);immature female,Tb=0.906*Ta + 9.608,r= 0.906(n=21);maturefemale,Tb=
0.827*Ta + 12.420,r=0.938 (n=32).
Morphologicalvariations inPantalaflavescens 153
and 1.085,respectively, andinmature males:0.885,0.757, respectively, inimma-
turefemales:0.906,0.906andinmaturefemales:0.938,0.827, respectively. There
was no significant differenceofboth coefficientsbetween thesexes orbetween
immatureandmature individualsofbothsexes (P>0.05, two-side, Z-test).
Themean Tb was 32.9±3.5°Cin immaturemalesand 34.9±3.4°Cin mature
males; 32.8±3.9°Cin immaturefemalesand36.2±4.5°Cinmaturefemales(Tab.
II).TheTbamongthesegroupswas significantly different(p =0.042,d.f.= 3,F
= 2.874, ANOVA-test)butonly the Tbof mature femalesdiffered significantly
fromothers (P< 0.05, t-test).
DISCUSSION
Pantalaflavescens fliesover to the Japanese mainlandinspring, and thefirst
recordisearlier(inearly andmidApril) atthecoastalareasof thePacific Ocean
such assouthernKyushu, Shikoku, andtheKantoregion andwestwardthanat
otherareas (Musashino Satoyama Research Group etal, 2004). Themeanfirst
recordfor23 yearsbetween 1973and 1995at Amakusa, KumamotoPrefecture
was May 17th, and the earliest datewas April 20th(TANAKA & HIGASHI,
2003).
Thelastrecordwas October25thatChichibuCity(ARAI, 1995).Therecords
from variousareas are mostly early and midOctober; earlierinHokkaido and
theTohokuregion, theNortheastof Japan,andlateratthecoastalareas ofthe
Pacific Oceanof theTokai region andwestward.The latestrecord, November
23rd, was reported by FUKUI (2005). TherecordfromKunugiyama seems to
bemoderate.
It deserves special mentionthat the sex ratioskewed towards femalesexcept
forthespecimens fromNagasaka. Eveninthespecimens collectedrandomly for
DNA sequencefromvarious areas inAsiait skewed towardsfemales, 57.0%, n
= 241 and43.0%, n= 182 inthemale(p <0.01, chi-square test)(HAYASHI &
ARAI,2004). However,according toKUWADA (1972) thesex ratioskewed to-
wardsmales(60%). Ambienttemperature,timezone, period orlocality mayin-
fluencethe sex ratio.
TANAKA & HIGASHI (2003) notedthat P.flavescens exhibitedtwo popu-
Table II
Thermal statistics ofPantalaflavescensatKunugiyamaforest(°C±s.d.)
Male Female
Immature Mature Immature Mature
Number 7 15 21 34
Bodytemperature (32.9±3.5) (34.9±3.4) (32,8±3.9) (36.2±4.5)
Ambienttemperature (26.9±2.9) (27.6±4.0) (25.6±4.0) (28.9±5.2)
154 N.Ishizawa
lationpeaks in KumamotoPrefecture, attheend of Juneandat theend ofAu-
gust,andARAI(1995) suspected thatthisspecies mighthavetwogenerations at
ChichibuCityaftercoming over there.Judging fromthetwo population peaks
at Kunugiyama, one between July and August and the otherfrom September
onward, Iagree withARAI (1995)on theassumption thatP.flavescens maybe
bivoltineat settlementson themainlandof Japan (except thenortherndistricts)
aftercomingfromoverseas.
Thefactthatadultsizeremainedfairlyconstantthroughout theseasonandthat
two population peaks wereobserved atKunugiyama (though size did decrease
alittleinthe lateseason) maysuggestno differenceoflarval durationbetween
each generation. TheindoorlarvaldurationofP.flavescens wasextremely short,
34-55days,andoutdoorsatapondoutsideitssouthernrangeinAustraliait was
51 days (HAWKING & INGRAM. 1994),so thatthe larval durationofeach
generation may beroughly estimated attwo months(TANAKA & HIGASHI,
2003). This is differentfromsomezygopteran species such as Ischnuraasiatica
(ISHIDAetal., 1989)andAciagrionmigratum(UDONO etal., 1997),wherelar-
valdurationandadultsize are differentbetween 1st voltineand2ndvoltine,and
theadultsoccurring lateinthe season are smaller.Theuniformity inthe sizeof
P.flavescens maybe dueto the shortlarvaldurationbetweenvoltines.
P.flavescens issaidtostartitsmigrationintheimmaturestage(CORBET, 1984,
1999). Accordingto ASAHINA&TSURUOKA (1967) allindividualscollected
onaweathershipattheTango weatherobservationspotonthePacificOceanin
August weremature;threemaleswerereddenedontheirabdominaldorsumand
the ovariesof femaleswere mature. I donot know the maturityofadultscom-
ing over to the mainlandin spring. However, as the above factshows, manyof
the migrating individualsin summer maybemature. Thisagreeswiththeshifts
of body weight and MDofthe individualsof Kunugiyama forest.Themature
individualsatKunugiyama inthe early season mightrepresentamixtureofthe
maturedescendantsofthefirstcomers tothemainlandinspring andthemature
migrantadultsfromsouthernoverseas.
Inautumn MD decreasedsharply. Asonly afewmature individualswereob-
servedinthis seasonandindividualsofseemingly soonafteremergencewerein-
cluded in the groupsat Kunugiyama, most ofthe individualsmight havebeen
thesecond generation thatresulted fromthemature adultsofthe early season.
As theshifts ofMDandPD show,itisassumed thatthematurityofthe second
generation maynot advance.MD of individualsof whichabdomenswerepru-
inescentexceeded4.6andtherewasnot sucha highcorrelationbetweenMDand
PD. Therefore, PD cannot beadecisiveindexof maturation.
WLofevenmaturefemaleswas significantlylowerthanthatofmaturefemales
of S. frequens (28.6±2.0 mg/cm2 n= 41), whichisamigratory species likePfla-
,
vescens (P <0.05) (Ishizawa, unpublished). Inthe malesP.flavescens, themean
WL for theseason was significantly lower than thatof the malesof Orthetrum
MorphologicalvariationsinPantalaflavescens 155
albistylum speciosum ofthe samesize, and also itwas thesamewhen compared
withthatofO. cancellatummalesfromEurope (26.4±2.54 mg/cm2)(GRABOW
&RUPPELL, 1995).Sincemostofmigratingfemalescaptured ontheocean were
mature(ASAHINA&TSURUOKA,1967;HASHIMOTO&ASAHINA,1969),
inP.flavescens, the lowWLmaybeadvantageous for itsmigratory dispersal.
FromSeptember onwardindividualsofWLlowerthan20 mg/cm2weremost
frequent, andinOctober mostindividualsofbothsexes weighed ca 15mg/cm2.
TheWLis as lowas thoseof someZygoptera (RUPPELL & HILFERT, 1993).
ARAI(2003) notedthatalthough manyP.flavescens swarms were sighted, their
ovipositionwas seenrarelyinsummer. P.flavescens isatropical species, hencelow-
eringofTamaysuppressmaturationandincreaseofbody weight, orWLmaybe
suppressed. This is different
fromthecaseof S.frequens,
inwhichbody weight increas-
es inearly and midSeptem-
beras Ta falls (ISHIZAWA,
2004, 2005).
AccordingtoMAY(1981),
wingbeatfrequency ofP.fla-
vescens was 22.9 Hz (25°C),
thelowest among species of
approximately thesame WL
of 20 mg/cm2. Therequired
power for fluttering flight is
proportional to the prod-
uctof the 5thpowerof wing
length (I) and the cubeof
wingbeatfrequency(/),while
theavailablepowerispropor-
Fig. 4. Relation of regressioncoefficient (REG) tocorrela-
tionalto the product of the
tioncoefficient(COR) in thepercher-typespecies andinthe
body mass(m)andthewing- flyer-type species. Data ofcoefficients of otherOdonata:
beatfrequency(f)(AZUMA, Anaxjunius(MAY, 1976), A.parthenopejulius (Ishizawa,
1987). Ignoring coefficients unpubl,),A. guttatus(ISHIZAWA,1998b),Anotogastersie-
of both equations; l5xfl = boldii (ISHIZAWA, 2003),patrollingCordulia aeneaamu-
rensis (Ishizawa, unpubl.),Mnais costalis oforange wing
m~xfP'X-fl =m. type(ISHIZAWA,2000),Orthetrumj.japonicum(Ishizawa,
In P. flavescens the wing unpubl.),O. albistylum speciosum(Ishizawa,unpubl.)and
length was unchanged as the both sexes ofSympetrumfrequensatreproductive period
season advanced. However, (ISHIZAWA, 1998a).The sex ormaturity ofA.juniuswere
body weight, as defined by unknown. Otherdata except forS.frequenswerefromma-
turemales. Least squares linear regressions are:thepercher
WL, decreased. Hence, the
type:adottedline,REG= 1.457*COR-0.099,r=0.766,p=
wingbeat frequency may de- 0.131;theflyertype:asolidline,REG=0.354*COR+0.046,
crease inthe autumn. As Tb r=0.907,p=0.034.
156 N.Ishizawa
andthe wingbeat frequency are positivelycorrelated, decrease of wingbeat fre-
quencybringsloweringofmetabolicheatproduction(MAY, 1981), so thatTb is
naturally lowered.
P.flavescens flieswithlessflutteringonthewindandlowerWLisadvantageous
forits flight. Thelatter may be disadvantageous for thermoregulation andtem-
peraturedependency inevitablybecomeslarge forthe dragonfly.Actually, between
bothsexes orbetweenmatureindividualsandimmatureindividualstherewas no
significant differenceofthe regression coefficientsofTbto Ta. They appeared
tobeaffectedbyTa andthiswas shownin thelargeregression coefficients.This
species belongs to theflyer type(CORBET, 1962) likeAeshnidaeandCordulii-
dae.Regression coefficientsofthe flyer type dragonflies tend tobe lower than
thoseof the percher type (Fig. 4). Theformerare mostly endothermicwhereas
thesecond are, in general,ectothermic(MAY, 1976, 1987).However, thoseofP.
flavescens approximate thoseofthepercher type.
Pflavescens isliableto swarmeveninhotdaytimeinmidsummer.ARAI(1995)
reported thatsomeofthoseswarmingwereseenflyingwiththeirabdomensbent
downward.ThiswasoftenobservedwhenTaexceeded30°Candthey flewagainst
thewindwiththisposture.Therefore, itisassumedthattheythermoregulate their
Tbbyexposing theirabdomensto thewind.CORBET(1999) describedthatthis
is aradiatoreffect.Inthis caselowWL mightbeprofitable forthem, onlyflying
driftinglyin the windwithless fluttering.Thehigh dependency on temperature
maysuppress maturationofthespecies inthecool autumn.
Thus, the swarm migrationsuch as observedby WAKANA(1959) mayprob-
ably beabehaviourforadaptation to suitableambienttemperatures.
ACKNOWLEDGEMENTS
Iwishtoexpressmycordial thankstoMr H.NARAOKA forprovidingliterature andforhiscrit-
ical readingofmy manuscriptand also toDrs K. HIGASHIand I.WAKANA foraccesstotheir
literature,and toananonymousreferee forhiscritical readingand correction ofmymanuscript.
REFERENCES
ASAHINA.S.&Y.TSURUOKA, 1967.Records oftheinsects visitingaweathershiplocatedatthe
OceanWeather Station ‘Tango’onthePacific.Kontyu35(4):353-360. [Jap.]
ARAI,Y., 1995. Somebiological observations ofPantalaflavescens inSaitama Prefecture. Gracile
53: 19-22.[Jap.]
ARAI,Y,2003. ProblemsonPantalaflavescensandSympetrumfrequens.In:Y,Arai,[Ed.],Acoun-
trywide survey ofred dragonfliesin2003, pp. 13-18,Musashino Satoyama Res.Gr. & Inst.
Agric. andNat. Environ.,Yorii-cho,Saitama. [Jap.]
AZUMA,A.,1987. Those magnificentmotionsoflivingcreatures.Kyontsu Shuppan,Tokyo.[Jap.]
CORBET,P.S.,1962. Abiologyofdragonflies.Witherby,London.
CORBET,P.S., 1984. Orientation andreproductivecondition ofmigratingdragonflies(Anisoptera).
Odonalologica13(1):81-88.