短報

OverwinteringEarlymaturationinmalesofthe

giantwaterbug,Appasz`smq/o7Esaki（Heteroptera:Belostomatidae）

Introduction

Thegiantwaterbug,Appas【(ｓ'"q/orEsaki,mhabits

shaUowwatersinmountainousregions,includingareas

dominatedbytraditionalricepaddies（Ichikawa，

1996).Populationsofthisspeciesaredeclininginmany

regionsinJapan・Becauseofthedecline,Ａ・〃!q/oris

includedinthelocaleditionofthereddatalistinlOof

47prefectures（AssociationofWildlifeResearch＆

EnVision,2007)．Despitethedeclineinpopulation

numbers,littleisknownregardingthelifecycleofthis

spec1es

Somestudies（Ichikawa,1996;Mukaiandlshii,2007）

showthatA・ｍｑ/oradultsoverwinterandreproducein

JuneandJuly・Thenewlyemergedadultsthenappear

fromlateJulyonwards､AppasMlM71qﾉorpreferscooler

watersthanthecongenericspecies,Ａ・ノapo"jc“

Vuillefroy（OkadaandNakasuji,1993)．Previous

studiessuggestthatA・n1Uorhasastrictunivoltinelife

cycleintheirnaturalhabitat（Ichikawa,1989,1993；

Mukaiandlshii,2007).Conversely,Ａ・ﾉCZpo"icwisable

toproducel-2generationsinasingleyear（Okada

andNakasuji,1993).Thedifferencemayberelatedto

environmentalfactorssuchastemperature・Appzzszls

ﾉapo"ｉｃＭｓｌｉｖｅｓｉｎｗａｒｍｅｒｗａｔｅｒｗｈｉｃｈｉｓｌikelyto

increasetherateofdevelopmentwhereasA､mqjo7live

incoolerwaterwhichmaylengthenthedevelopmental

perio。（OkadaandNakasujil993)．Inthepresent

study,afieldworkusingmarkandrecapturecensuses

wascarriedoutinawarmerwetlandthaninprevious

studies（OkadaandNakasuji,1993;Ichikawa,1993),in

ordertorevealthelifecycleofAJ7zqjorunderdifferent

thermalconditions

Shin-yaOhba1)＊andPabloPerezGoodwyn2】

l）LaboratoryofInsectEcology,GraduateSchoolofEnvironlnentalScience,OkayamaUniversity，

Okayama700-853qJapan2）LaboratoryoflnsectEcology,GraduateSchool

ofAgriculture,KyotoUniversity,Kyoto606-8502,Japan

(Rcceivcd：Novcmbcr27,2008；Acccptcd:January31,2009）

これまでの研究では，比較的冷涼な湿地に住む，オオ

コオイムシＡﾉﾌﾞp“【1ｓ（＝Djplo,ﾘc/i“），"qﾉ0,.の新成虫のオスは，野外において翌年の春まで卵塊を保護しないこ

とを強調している．しかしながら，本研究は水温が高い

ハピタットでは新成虫のオスが羽化し，越冬する前に卵

塊を保護することを示した．本調査地は，以前の野外研

究が行われていた生息地よりも水温が高く，そのことが

幼虫の発育を早め，初期（７月）に羽化した個体が成熟

したものと考えられる．本研究は，オオコオイムシのオ

スの新成虫が，野外において卵塊を保護していた初めて

の報告である．

Previousｓｔｕｄｉｅｓｈａｖｅｓｈｏｗｔｈａｔｔｈｅｎｅｗｌｙｅｍｅrged

adultsofthegiantwaterbu9,Ａ〃ａｓ“（DjpJolZych“）

ｍｑ/o）Esaki，donotreproduceuntilthefollowing

springincoolhabitats・WeobservedthelifecycleofA

l7zq/oﾉ･inawarmwaterenvironment・Ourresults

suggestthatatleastsomenewgenerationmales

carryeggmasses（encumbered）successfuUy

beforeoverwintering・Theencumberedadultmales

ofthenewgenerationappearedbetweenJulyand

August（newmales/totalmales:１/３１ｉｎJuly;８/２６

ｉｎAugust)．Wehypothesizethatthewarmer

environmentenhancesthespeedofdevelopmentThus

earlyemergingadultmalesareabletomaturepriorto

winterbecauseofthelong-dayphotoperiodinJuly、

Thisisthefirstreportdocumentingthepresenceof

encumberednewgenerationA〃皿/orInalesintheir

naturalhabitatbefOrewinter．

MaterialsandMethods

Thestudywasconductedinafallowricefieldin

Misaki（34.581Ｎ，133.58'Ｅ)，Okayamaprefecture

betweenAprilandOctober，2006．Wemeasuredthe

seasonalabundanceｏｆＡ'72q/orbyconductingfield

surveys､Weconductedthesurveysina１９．８㎡ａｒｅａｏｆ

ａｄｉｔｃｈｌｏｃａｔｅｄａｌｏｎｇｔｈｅｒｉｄｇｅｏｆthefallowricefield

Theditchreceiveddirectsunshineduringtheday,and

wasElledwithwater（5-15cmdepth）throughoutthe

studyperiod

WecapturedadultsusingaD-framedipnet（２８ｃｍ

Ｋｅｙｗｏｒｄｓ：Ａ〃αswJwWoj.，Belostomatidae，Ｎｅｗ●

generationmales，Ｅｇｇｓ，WatertemDerature1

JpnJ､EnvironEntomoLZooL20（１）：２７－３０（2009）環JilLも鮒20巻鮒１１J．：２７－３０（2009）CorrespondinEauthor：oobuR＠hotmaiLcom

－２７－

Shm-yaOhbaandPabloPerezGoodwyn

inwidth,３ｍｍｍｅｓｈ)．Eachadultwasindividually

numberedonthethoraxusingpaintmarkers（Paint

MarkerqMitsubishi）andweresubsequentlyreleased

intotheditch､Werecordedtheindividualnumber,ａｇｅ

(overwinteredornewgenerationadults),sex,ａｎｄｔｈｅ

ｎｕｍｂｅｒｓｏｆｅｇｇｓｏｎｔｈｅｂａｃｋｏｆthemalespriorto

release,Newgenerationadultswereeasilyrecognized

bytheircleanwingsand/ｏｒｓｏｆｔｂｏｄｙ・Wethen

surveyedthestudysiteonaweeklybasisthroughout

thestudyperiod,twentysixtimesintotaLInadditio､，

wemeasuredwatertemperatureduringeachsurvey、

WeusedtheJoUy-Sebermethod（Jolly,1965;Seber，

1965）toestimatethenumberofadultspresentduring

eachsurvey､ToevaluatetherelativeabundanceｏｆＡ

ｍｑﾉornymphs,ｔｈｅＤ－ｈｆａｍｅｄｉｐｎｅｔｗａｓｓｗｅｐｔ２０ｔｉｍｅｓ

ａｌｏｎｇａ５０ｃｍｐａｔｈａｃｒｏｓｓｔｈｅｗａｔｅｒSurface・This

procedurewasrepeated3times・Ｗｅｃｏｕｎｔｅｄｔｈｅ

ｎｕｍｂｅｒｏｆｎｙｍｐｈｓｆｒｏｍｅａｃｈｉｎｓtar、Datafrom

publishedliteraturewasusedtocomparewater

temperatureofthepresentstudywithotherstudyto

otherstudysites（OkadaandNakasuji,1993;Ichikawa

l993)．

Ｗｅｃｏｍｐａｒｅｄｔｈｅｎｕｍｂｅｒｏｆｅｇｇｓｃａｒｒｉedby

overwinteredandnewgenerationmalesusing

Student1sr-test・Watertemperaturewascompared

usingtheWilcoxonsignedranktest,withmonthasa

replicate・Beforeanalysis，monthlymeanwater

temperaturewascalculatedusingdailydatafbreach

month・ＣｏｍｐarisonsinwhichP<0.05,wereconsidered

statisticallysignificantAllstatisticaltestswere

conductedusingJMPsoftware（JMPversion70,ＳＡＳ

Institute,2007)．

generationmalesinAugust,suggestingthathatching

wassuccessfuLThewatertemperaturewas

significantlyhigheratthepresentstudysitethanat

studysitesinpreviouslypublishedresearch（TabIel)．

Appasz（s'7zcvo/･tendedtodevelopmorerapidlyinthe

presentstudythaninpreviousStudies（Okadaand

Nakasuji,1993;Mukaiandlshii,2007)Eachinstarwas

observedaboutlmonthearlierthanintheprevious

印加印叩卯０如加、⑩０如卯、伯０如卯、価０如卯印加０如卯如扣０

２２１１

Ａｄｕｌｔｓ

ｉｎｓｔａｒ

の一ｍ二つ一シモニ．○之

Ｓｅｃｏｎｄｉｎｓｉａｒ

Ｔｈｉｒｄｉｎｓｔａｒ

ReSn1tSandDiRCusSion目ｏｕｒｔｈｉｎｓｔａｒ

OverwinteredadultsweremostabundantinApril

(Fig.１)Encumberedmalesappearedatthestudysite

betweenAprilandAugust・Nymphsappeared世ｏｍ

ｍｉｄＭａｙｏｎｗａｒｄｓ，andnewgenerationadults

appearedbetweenJulyandOctober・Encumberednew

generationmalesappearedbetweenJulyandAugust

(newgenerationmales/totalmales:１/３１fbrJuly,８/２６

fbrAugust,Fig.２)．Allencumberednewgeneration

maleｓｈａｄｅｍｅｒｇｅｄｉｎＪｕｌｙ・Overwinteredmales

carriedsignificantlymoreeggsthannewgeneration

males（overwinteredmales:77.13±10.94（ｍｅａｎ±

SE)，31-115（range)；newgenerationmales:47.71±

3.09,31-56;卜test:〃＝13,『＝2.431,Ｐ＝0.030)．We

observedeggshellsamongtheclutｃｈｏｆｔｗｏｎｅｗ

日iｆｔｈｉｎｓｔａｒ

Apr・ＭａｙＪｕｎ、Ｊｕｌ・Ａｕｇ・ＳｅｐＯｃｔ

Ｆｉｇ．１AbundanceandphenologyofAppas“'72qﾉo）．,Ｔｈｅｄａｔａｒｅｐｒｅｓｅｎｔｔｈｅｍｅａｎａｎｄｖａｒｉａｎｃｅ

（calculatedbyJolly-Sebermethod）orstandarderrorforadultsandnyｍｐｈｓ，respectively・The

overwintered（blackcircles）ａｎｄｎｅｗｌｙｅｍｅｒｇｅｄ（whitecircles）adultsareshownseparately．

－２８－

EarlymaturatloninmaleA〃α・ｍＪｗ"qﾉ０１℃

earlymaturationofnewgenerationmales（Tableｌ)．

Thewarmwatertemperaturesappearｔｏｈａｓｔｅｎ

ｇｒｏｗｔｈｏｆｔｈｅｎｙｍｐｈｓａｎｄｆａvorearlyemergenceof

youngadultsinJuly・Photoperiodisalsolikelytoplay

akeyroleinreproductivesuccess・Ｆｏｒexample,short‐

dayphotoperiodsduringlatesummeｒａｎｄａｕｔｕｍｎ

ｉｎｄｕｃｅｒｅｐｒｏｄｕｃｔｉｖｅｄｉａｐａｕｓｅｉｎｎｅｗＫｉｒＡｇｃｚｌｄ)'iα

(Leﾉﾉzoce'･"s）ｄｅｊﾉroﾉﾉﾊﾞBelostomatidae）adultｓ

(HasizumeandNumatal997)．Assumingthatday-

lengthalsoplaysaroleininducingdiapauseinA．

"１qjoﾉ；thenewgenerationmalesmayhaveemerged

earlyenough（July）ａｔｏｕｒｓｔｕｄｙｓｉｔｅｓｕｃｈｔｈａｔ

ｒｅｐｒｏｄｕｃtionwasnotaffectedbyday-length、

Conversely，malesemerginginAugustorlater，are

likelytoenterreproductivediapauseduetotheshort‐

dayphotoperiod

Newgenerationmalescarriedsignificantlyfewer

eggsthanocerwinteredmalesWespeculatethatｔｈｉｓ

studiesWealsoobservedeggmassesonnewgeneration

males（Fig.２).BecauseA・''２q/ormalesattemptto

copulatebeforereceivingeggstosaaurepaternity，

thesenewgenerationmaleswereUkelyreproductively

mature（Ichikawa,1989)．Moreover,thepresenceof

hatchedeggsheUsindicatesthattheeggswereviable・

However,wecannotruleoutthepossibilitythatthe

eggswerefertilizedbyspermfromanothermale

storedinthefemalesspermatheca（Smithl979a)．

Ourobservationsoftheencumberednewgeneration

malesbeforewinterdifferfrompreviousreports，

ｗｈｉｃｈｄｏｃｕｍｅｎｔｅｄｕｎｉｖｏｌｔｉｎｉｓｍｉｎｔｈｉｓｓｐｅｃｉｅｓ

(Ichikawa,1989,1993；OkadaandNakasuji，1993；

MukaiandlshiL2007）．Wehypothesizethat

environmentalｆａｃｔｏｒｓａｒｅｒｅｓｐｏｎｓｉｂｌｅｆｏｒｔｈｅ

ｄｉｆｆｅｒｅｎｃｅｉｎｔｈｅｌｉｆｅｃｙｃｌｅａｔｔｈｉｓｓｔｕdysiteThe

combinationofwarmwatertemperaturesandalong-

dayphotoperioddurinRJulylikelycontribuｔｅｔｏｔｈｅ

1００

の－，コで一ンもこ一．○二

鴬 Newgenerationmales１８１０

■ OveMinte｢eｄｍａｌｅｓ810

4０

Ni1NNS1liNS1iEIU

0１

Ａｐｒ，ＭａｙＪｕｎ、ＪｕｌＡｕｇ，ＳｅｐＯｃｔ

Fig.２Seasonalfluctuationintheabundanceofencumberedmales

TablelComparisonofwatertemperatureinthestudysitewiththatofpreviousstudies

Meanwatertempemturel Studysite Reference

25.6

21.4゛

16.9動

１９．０．

１８１゛

MisakLOkayama Presentstudy

WesternHyogo Ichikawa(1993）

TsuboiPkayama OkadaandNakasuji(1993）

KanayamaPkayama OkadaandNakasuji(1993）

KukoPkayama OkadaandNakasuji(1993）

１）FromApriltoSeptember

･ThewatertemperatureinallpreviousstudysitewassignificantlylowerthaninMisaki（P<0.05,Wilcoxonsignedranktest)．

－２９－

Shm-yaOhbaandPabloPerezGoodwyn

ｍａｙｂｅｄｕｅｔｏｓｅｌｅｃｔｉｏｎｆＯｒｔｈｅｏｌｄｅｒｍａｌｅｓｂｙｆｅｍａｌｅｓ

(Smithl979b)．Althoughwewereabletodocument

reproductioninyoungmalespriortooverwintering

wewerenotabletodeterminethereproductive

successofyoungfemales

Insummary，ourresultsshowthatenvironmental

conditionscanplayaroleindeterminingthelifecycle

ofAmqjoﾉzInwarmwaterandunderlongday-length

photoperiodsbivoltinismislikelytobefavored

Conversely，itappearsthatcoolwatertemperatures

favorunivoltinism、However，furtherresearchis

neededtodeterminethefitnessofoffSpringcarriedby

theyoungermales．

ReferenceS

AssociationofWUdlifeResearch＆EnVision（2007）

Ｓｅａ元ASysre"ＺｑｆﾉﾋZpα'zeseだ。ｄｔｚｍ・Availablefrom：

http://www・jpnrdb・com/index・hｔｍｌ（asonlOth

November2008)．

Hasizume,ＨａｎｄＨＮｕｍａｔａ（1997).､ノア".ＬＥ'Zr。'"０１．６５：５５－６１．

Ichikawa,Ｎ､（1989）ノ.Ｅ『ﾉ１０ﾉ.７：133-140．

Ichikawa,Ｎ（1993）A9z(αbiologyl5：192-197．（In

JapanesewithEnglishAbstract）

Ichikawa,Ｎ（1996）ルノVUrZlreα'1．ﾉ７１sｅｃｒｓ３１（11）：

８－１１．（ｉｎJapanese）

JoUy,ＧＭ．（1965）Ｂｉ。'j1errikzz52：225-247．

Mukai,Ｙ・ａｎｄＭ・IShii（2007）Ａｐｐｌ・E7Zro'"oLZboJ.４２：５９５－６０５

０kada,ＨａｎｄＦ・Nakasuji（1993）ＪＰ".Ｊ､Erlrol7zoﾉ.６１：

７９－８４．

Seber,Ｇ,Ａ､Ｆ、（1965）Bio"zarjAa52：249-259．

Smith,ＲＬ.（1979a）Scie,Ice205：1029-1031．

Smith,Ｒ・Ｌ（1979b）Ａ"i,"､BeAQv､２７：716-725.

Acknowledgments

ＷｅｗｏｕｌｄｌｉｋｅｔｏｔｈａｎｋＰｒｏｆＴ・MiyatakeandDr.Ｋ、

ShimizuofOkayamaUniversityfortheirvaluable

comments・ＷｅａｒｅｇｒａｔｅｆｕｌｔｏＭｒ・Ｔ・Ｋojimafor

providmgtheJolly-Seberprogram､ＷｅａｌｓｏｔｈａｎｋＫ

KatofOrhiskindsupportwiththefieldsurveys．

－３０－