Take-Off Time of the First Generation of the Overwintering Small Brown Planthopper, Laodelphax

20 Pages·2015·1.45 MB·English

RESEARCHARTICLE
Take-Off Time of the First Generation of the
Overwintering Small Brown Planthopper,
Laodelphax striatellus
in the Temperate Zone
in East Asia
SachiyoSanada-Morimura1,AkiraOtuka1*,MasayaMatsumura1,TomokiEtoh2,
YeqinZhu3,YijunZhou4,GufengZhang4
1 KyushuOkinawaAgriculturalResearchCenter,Koshi,Kumamoto,Japan,2 SagaPrefecturalAgriculture
ResearchCenter,Saga,Japan,3 PlantProtectionStationofJiangsuProvince,Nanjing,JiangsuProvince,
People’sRepublicofChina,4 InstituteofPlantProtection,JiangsuAcademyofAgriculturalSciences,
Nanjing,People’sRepublicofChina
* [email protected]
Abstract
OPENACCESS
Citation:Sanada-MorimuraS,OtukaA,Matsumura Overseasmigrationofthesmallbrownplanthopper,Laodelphaxstriatellus(Fallén),occurs
M,EtohT,ZhuY,ZhouY,etal.(2015)Take-OffTime duringthewinterwheatharvestseasoninEastAsia.Knowingthetake-offtimeofemigrat-
oftheFirstGenerationoftheOverwinteringSmall
ingL.striatellusiscrucialforpredictingsuchmigrationswithasimulationtechniquebe-
BrownPlanthopper,Laodelphaxstriatellusinthe
causewinds,carriersofmigratoryinsects,changecontinuously.Severalmethodswere
TemperateZoneinEastAsia.PLoSONE10(3):
e0120271.doi:10.1371/journal.pone.0120271 usedinChinaandJapanfromlateMaytoearlyJune2012andagainin2013toidentifythe
precisetimingoftake-off.Thesemethodsincluded:atownettrapmountedtoapoleat10m
AcademicEditor:RaulNarcisoCarvalhoGuedes,
FederalUniversityofViçosa,BRAZIL abovetheground,ahelicopter-towednettrap,andacanopytrap(whichalsohadvideo
monitoring)setoverwheatplants.Laodelphaxstriatellusemigratedfromwheatfieldsmainly
Received:August19,2014
intheearlyevening,beforedusk.Theinsectsalsoemigratedduringthedaytimebutrarely
Accepted:February3,2015
emigratedatdawn,showingapatternthatisunlikethebimodalemigrationatduskand
Published:March17,2015 dawnoftwootherriceplanthoppers,thebrownplanthopper,Nilaparvatalugens(Stål),and
Copyright:©2015Sanada-Morimuraetal.Thisis thewhite-backedplanthopper,Sogatellafurcifera(Horváth).Therewasnosignificantdiffer-
anopenaccessarticledistributedunderthetermsof
enceinthetemporalpatternoftake-offbehaviorbetweenfemalesandmalesofJapanese
theCreativeCommonsAttributionLicense,which
L.striatelluspopulations.
permitsunrestricteduse,distribution,and
reproductioninanymedium,providedtheoriginal
authorandsourcearecredited.
DataAvailabilityStatement:Allrelevantdataare
withinthepaper.
Funding:Thisworkwasfundedbythescienceand Introduction
technologyresearchpromotionprogramfor
agriculture,forestry,fisheriesandfoodindustry,No. Long-distancemovementisoneoftheprimaryreasonsfortheevolutionarysuccessofinsects
24018(2012-2013),andaresearchprojectentitled throughouttheworld[1].Insomeinstances,insectspeciesmigratelongdistancesutilizingfa-
“Developmentoftechnologiesformitigationand
vorableupperwinds,andoccasionallyevenflyovertheoceanintoanothercontinent,i.e.the
adaptationtoclimatechangeinAgriculture,Forestry
paintedladybutterfly,Vanessacardui(Linnaeus)[2,3].Long-distancemigrationisproblemat-
andFisheries”(2012-2013).Bothfundswerefromthe
icespeciallywhensomeviruliferousinsectpeststhatdamageagriculturalcropsinoneareacan
MinistryofAgriculture,ForestryandFisheriesof
Japan.Thefundershadnoroleinstudydesign,data migrateintonewunaffectedareasandtransmitpathogenicvirusestocrops,causingserious
PLOSONE|DOI:10.1371/journal.pone.0120271 March17,2015 1/20
Take-OffTimeofLaodelphaxstriatellusinEastAsia
collectionandanalysis,decisiontopublish,or damage.Suchexamplesincludesomeaphidspecies[4].Otherinsectpestsmigrateregularly
preparationofthemanuscript. onlyincertainregionsandseasons.Therefore,itisimportanttounderstandthefactorscon-
CompetingInterests:Theauthorshavedeclared trollingthetimingandmigrationroutesofmigrantinsectpests.Tounderstandmechanismsof
thatnocompetinginterestsexist. migration,variousmethodssuchasbehaviorobservation,geneanalysis,meteorologicalanaly-
sisandradarobservationhavebeenemployed[5].Forexample,extensiveinvestigationsonthe
migrationinEastAsiaofthebrownplanthopper,Nilaparvatalugens(Stål)andthewhite-
backedplanthopper,Sogatellafurcifera(Horváth),majorinsectpestsofrice,haverevealed
theirmigrationsource,migrationroutes,take-offbehaviorsandotherimportantaspectsof
theirlifehistories[6–10].
Thesmallbrownplanthopper,Laodelphaxstriatellus(Fallén)isanotherimportanteconom-
icinsectpestofriceinEastAsia.ThisinsecttransmitsRicestripevirusandRiceblack-streaked
dwarfvirus[11,12].Thetwoviruseshaverecentlyre-emergedinEastAsia,includingeastern
ChinaandcentralJapan,since2000[13–16].Mostnotably,anoutbreakofL.striatellusoc-
curredinJiangsuProvinceinChina,andviruliferous,firstgenerationprogenyofoverwintering
L.striatellusoccasionallymigratedoverseastowesternJapanandKoreainlateMaytoearly
June[12].Thisshortperiodcorrespondstothewheat-harvestingseasonintheprovince,when
alargenumberofnewlyemergedinsectsofthefirstgenerationemigratefromharvesting
wheatfieldstofindnewhosts,riceplants,producingmassemigrationsthatoccuronlyoncea
yearduringthisseason[17].Anoutbreakofricestripedisease,forexample,occurredin2008
alongtheJapanesewesterncoastalregionsafterthefirstgenerationofanoverwintering
L.striatelluspopulationimmigratedfromoverseasintowesternJapan[18].InNagasakiprefec-
ture,oneofthemostwesternprefectures,theoccurrenceofL.striatellusinthatyearsharplyin-
creasedby126%fromthepreviousyear[12,18].
PredictionofsuchoverseasmigrationsofL.striatellusinEastAsiaprovidesbasicinforma-
tionontheinsects’arrivaltimesandareastolocalplantprotectionstationsandfarmers,andis
oneofthemostimportantmethodsformonitoringpossiblemigrationsinadvanceandforeffi-
cientlycontrollingimmigrantsandtheirvector-bornediseasessubsequenttomassimmigra-
tions.Forecastedarrivaltimingisusedtopredicttheemigrants’growthstageorthepreferable
timingforchemicalcontrol.Predictedarrivalareasarealsousedtoidentifypossibleareasfor
investigatingtheoccurrenceofthepestandforcontrol.Toforecastlong-distancemigrations
ofL.striatellusasaccuratelyaspossible,apredictionmethodhasbeendeveloped[19].The
methodconsistsoftwosteps:predictionoftheperiodforinsectemigrationineasternChina
basedontheeffectiveaccumulatedtemperatureandpredictionofinsectmovementwithami-
grationsimulationmodelduringaforecastemigrationperiod[19].Thesimulationmodel
needstheinitialtimeoftakingofftoinitiateacalculation.Take-offatduskanddawnwereten-
tativelyusedinaccordancewiththeobservedbehaviorofN.lugensandS.furcifera[10,20,21]
sinceobservationsofL.striatellustake-offarelimited.
Previously,monitoringofL.striatellusimmigrantsintoricepaddyfieldsinJapanwascon-
ductedatone-ortwo-hourintervalsinJunewithyellowwater-pantrapsplacedinthepaddy
fields.Usingthismethod,catchpeaksoccurredaround0500–1100hand1500–1800hJapanese
StandardTime(JST)[22].However,thismethodmonitoredtheinsect’simmigrationactivity
intothepaddyfields,notitsemigrationactivity,althoughthecatchesshouldbe,tosomeextent,
relatedtothetake-offtimefromwheatandbarleyfields.Inanotherstudy,hourlymonitoring
ofL.striatelluswithalighttrapwasconductedduringthewheatharvestseasonineastern
Chinaandpeaksofemigrantsweretrappedat2000–2100hChineseStandardTime(CST)and
smallcatchesweretrappedat0500h[23,24].However,thetake-offactivityinthedaytimeand
earlyeveningwasnotinvestigatedbythesestudiessincelighttrapsworkonlyduringthenight.
Furthermore,confirmationwasrequiredthatL.striatellusfliesathighaltitudesinamanner
similartoN.lugens,whichascendstomakeuseofwindsathighaltitudesforitsmigration[10].
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Take-OffTimeofLaodelphaxstriatellusinEastAsia
Insectsshowvariouspatternsofflightperiodicitybasedondatafromabouthalfamillion
speciescollectedinsuctiontrapsonthegroundintheUK[25].Usingentomologicalradar,the
numberoftargetsataltitudesinsummertypicallypeaksatduskanddawnandadaytimehigh-
valueperiod,aswellasanighttimelayeronsomeoccasions[26].Practically,thetake-offtime
directlyaffectsthepredictedarrivaltimeandareainamigrationsimulation,sincethewinds
thatcarryinsectschangecontinuously.Forthisreason,itiscrucialtoknowwhenL.striatellus
beginsitsemigrationinordertoimprovethepredictionquality.
Thisstudy,therefore,monitoredthetake-offtimeofemigrationofL.striatellusinlateMay
toearlyJuneinbothChinaandJapan.Themonitoringemployedseveraltrappingmethodsat
differentmonitoringheightssuchasacanopytrap,asuctiontrap,apole-mountednettrap,
andaballoon-supportedorhelicopter-towednettrap.
MaterialsandMethods
MonitoringthemigrationsourceinChina
ThesurveywasconductedbothineasternChinaandwesternJapan,wherewinterwheatand
summerricecropsaregrown.ThefirstgenerationofoverwinteringL.striatelluspopulations
inJiangsuProvincemostlyemigratesfromlateMaytoearlyandmiddleJune[17].Theobjec-
tiveofthesurveyinChinawastocharacterizethetake-offpatternofL.striatellusatthepossi-
blemigrationsource,wheretheinsect’sdensitywashigh;however,thenumberofmonitoring
locationsintheChinesesurveywaslowduetolimitedfunding.Therefore,thesurveyinJapan
aimedtoobtainreplicateddataonthenumberofL.striatellusemigrants,althoughtheinsect’s
densityinJapanwasrelativelysmall.
TwomonitoringsiteswereestablishedinJiangsuProvince,China.Jiangsuisamajoroccur-
renceareaofL.striatellusoccurrencehavinghadabout70%ofthetotalChineseRiceStripe
Virusoccurrenceareain2003[27],andpossiblyservingasasourceareafortheoverseasmi-
grationintoJapanandKorea[12].OnesiteislocatedinTongzhou(32.112°N,121.077°E,4m
abovesealevel(ASL))inthesouthernpartoftheprovincein2012,andtheotherinDongtai
(32.842°N,120.257°E,2mASL)inthecentralpartin2013(Fig.1).Theformersitewasselected
becauseanettrapwasalreadyinstalledinanexperimentalfieldfortheTongzhouPlantProtec-
tionStation.ThelattersitewasinanexperimentalfieldfortheDongtaiPlantProtectionSta-
tionandwasselectedbecausethedensityofL.striatellusinwheatfieldsat10locationsinthe
provincewascheckedinthemiddleofMay,2013andthatinDongtaiwasfoundtobesuffi-
cient.Theplantprotectionstationsissuedpermitsforlandusage.Nootherspecialpermission
wasnecessaryforthesesurveysbecausethesitesarenotlocatedinanyprotectedareaandno
protectedspeciesweresampledinthesurveys.AtownettrapwasusedattheTongzhousitein
2012andacanopytrapattheDongtaisitein2013.Althoughthetownettrapisoneofthe
standardmethodsformonitoringmigratinginsects,townettrapspossiblycapturebothlocal
emigrantsandimmigrantsfromoutsideofthelocalarea.Therefore,acanopytrapwasusedin
thesecondyeartocapturedirectlyonlyemigrantsfromwheatfields.
AttheTongzhousite,atownettrap1.5mindepthwitha1-mringwasmountedatthetop
ofapole10mabovetheground.Thefirstdateofthesurveyperiodwasdeterminedbyrefer-
ringtotheemergencedatesofthefirstgenerationoftheoverwinteringpopulation.Theemer-
gencedatewasestimatedbyL.striatellus’seffectiveaccumulativetemperaturefromthefirst
dayofeachyearwithamethoddescribedinZhangetal.(2012)[28].Thestageonthefirstday
wasassumedtobethe3rdand4thinstar,anddevelopmentalparametersused(thedevelop-
mentalzero,developmentalstoptemperatureandeffectiveaccumulativetemperatureforeach
stage)wereestimatesoftheChinesepopulation[28].Dailyairtemperaturedatausedwere
thoseinTongzhouobtainedfromChineseweatherdatabase(http://www.weather.com.cn).
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Take-OffTimeofLaodelphaxstriatellusinEastAsia
Fig1.Locationmapofsurveysites.
doi:10.1371/journal.pone.0120271.g001
TheestimatedemergencedaterangedfromMay30toJune3andtheadultstagerangedfrom
May30toJune10,2012.Thefirstdayofthesurveybeganseveraldaysbefore30May.Thelast
dateofthesurveyperiodwasdeterminedwhenlargenumbersofinsectswerecaughtinthenet
trap.Consequently,insectscaughtinthetrapwerecollecteddailyat0900hCSTfromMay25
toJune14,andwerecollectedfrequentlyat0440,0700,0900,1200,1500,1800,1900,2000and
2100hCSTfromJune8to11.Duringthefrequentmonitoringperiod,insectswerenotcollect-
edwhenitrainedheavily.
TheinvestigationperiodatDongtaiin2013wasfromMay31toJune6.Thesedateswere
determinedsimilarlyasdescribedabove[28],exceptthatthetemperaturedataatDongtaiwere
usedtocalculatetheeffectiveaccumulativetemperatures.Theestimateoftheemergencedate
rangedfrom3to7JuneandtheadultstagerangedfromJune3to13,2013.Twocanopytraps
(Fig.2a)tomonitorthetake-offofL.striatellusdirectlyfromwheatplantsweresetupover
wheatfieldsat1700hCSTonMay31,andmonitoringwasoverat0700hCSTonJune08
(Table1).Trappedinsectswerefromanaturalpopulationattwowheatplots,andnoinsects
wereaddedartificiallyintotheplotsfromoutside.Thedistancebetweenthetwotrapswas
about50m.Acanopytrapconsistedofthreemajorparts:analuminumcanopyframe
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Take-OffTimeofLaodelphaxstriatellusinEastAsia
Fig2.Canopytrapandhelicopter-towednettrap.a.Canopytrapoverwheatplants.Laodelphax
striatellusflewdirectlyupintotheacrylicbox,orinsectsflewontotheplasticsheetandthenwalkedintothe
box.b.Helicopter-towednettrapintheair.Thephotowastakenfromthecabinlookingbelowthehelicopter.
Thetraphastwogatesatthetailofthemeshnet.Thetailgatewasclosedwhensamplingstartedatabout
260mhigh,andthefrontgateclosedwhenthesamplingended.Thehelicoptermaintaineditsflightspeed
(65km/h)andheightfor20minduringeachsampling.
doi:10.1371/journal.pone.0120271.g002
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Take-OffTimeofLaodelphaxstriatellusinEastAsia
Table1. CanopytrapsettingsatDongtai,Jiangsuprovince,China.
Date Samplecollectiontime(h) Videorecordingmode Remark
Period CT1 CT2
May31 - - - Installationat1700
Jun1 0700 - -
1900 - -
Jun2 0700 0735–1900 - Visible Recordingstartedat0700
1900 1935–0700 Infrared Infrared
Jun3 0700 0735–1900 Visible Visible
1900 1935–0700 Infrared Visible
Jun4 0700 0735–1900 Visible Visible
1900 1935–0700 Infrared Visible
Jun5 0700 0735–1900 Visible Visible
1900 1935–0700 Infrared Visible
Jun6 0700 0735–1900 Visible Visible
1900 1935–0700 Infrared Visible
Jun7 0700 0735–1900 Visible Visible
1900 1935–0700 Infrared Visible
Jun8 0700 - - Monitoringendedat0700
doi:10.1371/journal.pone.0120271.t001
consistingofasquarepyramid(260×260×60cm)withfour144-cmlegsatthecorners(Cole-
manJapanCo.,Ltd.,EasyCanopyUltraLight/260),ameshscreen(ColemanJapanCo.,Ltd.,
MeshScreenHangerforEasyCanopyUltraLight/260)suspendedfromthecanopyframe,
andantransparentacrylicbox(30×30×30cm)withasquarehole(65×65mm)atthebottom,
placedonanaluminumbaseframeoverthetopofthecanopyframe(Fig.2a).Thetrapen-
trance(thesquarehole,about220cmabovetheground)andasquareaperture(120×120cm)
ofthemeshscreenatitstopwereconnectedwithatransparentplasticsheet.Themeshscreen
wascuthorizontallyatabout25cmabovethetopofthewheatplantstopreventinsectsfrom
walkingindirectlyfromthewheatplantstothemesh.Duringthemonitoringperiod,thenum-
berofL.striatelluscaughtinthecanopytrapwascountedat0700and1900hCSTdailybytwo
oftheauthors.Ittookabout35mintocollectinsects,changethememorycardandvideore-
cordingmode(seebelow),andtoputtheacrylicboxbackontopofthecanopytrap.Therefore,
insectswerenotcollectedduringtheperiodsof0700–0735and1900–1935hCST(Table1).
Theinsectscollectedwereputinarefrigeratorat-20°Cforsometimeandcountedtodeter-
minetheirflightactivitiesindayandnighttimes.
Inaddition,adigitalvideocamera(SonyCorporation,HDR-CX720V)wasplacedinthe
boxtorecordthetimeofeachinsect’sentrythroughthehole.Thevideocameraoncanopy
trap1(CT1)usedthevisiblelightmodeforrecordingduringthedayfrom0700to1900hCST,
andtheinfraredlightmodeduringthenightfrom1900to0700hCST(Table1).Thevideo
cameraoncanopytrap2(CT2)mostlyusedvisiblelighttorecordinsectsatdawn(Table1),
becausenoinsectswererecordedintheinfraredafter0500hCSTduetothesaturationofin-
fraredimagesbythebrightnessofmorningsunlight.Noinsectswererecordedinthevisible
lightmodeduringthenightduetoinsufficientlighting.Thenumberofinsectscollectedfrom
thecanopytrapsandseenonthevideowerenotcomparedandweredealtwithseparately,be-
causesomeinsectsthatflewdirectlyintothecanopytrapcouldnotberecognizedinthevideo
duetotheirfastmovement.
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Table2. Monitoringmethodsandparameters.
Location Monitoringmethod Surveyperioda Operationhours(JST)/ Samplingintervals/sampling
numberofflight durationperflight
May26-June5, May24-June8,
2012 2013
Site1 Nettrapat10m P P 24h 1,2h
(S1)
Nettrapat5m P 24h 1,2h
Balloon-towednettrapat P P 0430–2100 1,2h
20m
Suctiontrapat1.7m Pb P 24h 1,2h
Lighttrapat1.5m P P 1800–0600 Daily
Site2 Balloon-towednettrapat P P 0430–2100 1,2h
(S2) 10m
Suctiontrapat1.7m Pb P 24h 1,2h
Lighttrapat1.5m P 1800–0600 Daily
Airport Helicopter-towednettrap Pc 6flights 20min
at260m
aP:Eachmonitoringwasperformed.
bOperationin2012waslimitedfrom0430to2100h.
cSuveydate:May31,2013.
doi:10.1371/journal.pone.0120271.t002
MonitoringinJapan
TheJapanesesurveywasconductedtomonitorL.striatellusemigrantsatdifferentaltitudesin
twolocationsfortwoyears.TwomonitoringsiteswereestablishedinSagaPrefecture,western
Japan(Fig.1).Site1(S1)islocatedat33.218°N,130.311°E,2mASLattheSagaPrefecturalAg-
ricultureResearchCenterwhoissuedthepermitoflandusage.Site2(S2)waslocated10.9km
northeastofS1(33.294°N,130.385°E,1mASL)andisaprivatepropertywhoseownerissued
thepermitforlandusage.Nootherspecialpermissionwasnecessaryforthesesurveysbecause
thesitesarenotlocatedinanyprotectedareaandnoprotectedspeciesweresampledinthesur-
veys.Bothsitesweresurroundedbywheatandbarleyfieldsthatwerereadyforharvest.Surveys
tomonitorL.striatellusemigrationwereconductedfromlateMaytoearlyJunein2012and
2013(Table2).Thefirstdayofthesurveyperiodsforbothyearswassimilarlydeterminedby
L.striatellus’seffectiveaccumulativetemperaturesasdescribedabove,exceptusingdevelop-
mentalparametersoftheJapanesepopulation[19].Airtemperaturedatausedwerethosefrom
SagaWeatherStationabout3.2kmnorthofS1.Estimatedemergencedatesin2012and2013
were27Mayand28May,respectively,andthesurveyperiodforeachyearstartedafewdays
beforethecorrespondingestimate(Table2).
Severaltypesoftrapswereusedtocaptureinsectsatdifferentaltitudes(Table2).AtS1in
2012andbothsitesin2013,alighttrapwitha60wattelectricbulbat1.5mabovetheground
(AGL)andafunnelbeneaththebulb(IkedaScientificCo.,Ltd.,MT-7-N)wereused.Thetrap
wasoperatedfrom1800to0600hJSTtocollectinsectsduringthenight.
ThesuctiontrapwasaJohnson-Taylortype[29]paintedyellow;anet80cmindepthwitha
60-cmcircularaperturewasmountedat1.7mabovethegroundtoaverticalcircularcylinder
1mlongand70cmindiameter,underwhicha400-wattfan60cmindiameter(Mitsubishi
ElectricCo.,Ltd.,EG-60ETB-PR)wasinstalledat70cmabovethegroundtomoveairintothe
cylinder(9210m3/h).Suctiontrapswereoperatedduring0430–2100hJSTin2012,andfor24
hin2013(Table2).
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Take-OffTimeofLaodelphaxstriatellusinEastAsia
The10-mnettrapwasthesametypeasthatusedinTongzhou,Chinaandwasusedonlyat
S1(Table2).In2013,anadditionalnettrapofthesamesizewasmountedat5mabovethe
groundonthesamepoleasthe10-mnettrap,inordertocatchinsectsatalowerheight.The
nettrapswereoperatedfor24h.
Theballoon-suspendednettrapconsistedofahelium-filledcaptiveballoon2.3mindiame-
terandatownettrap80cmindepthwitha60-cmringattachedtoasupportingropeunder
theballoon.Theheightoftheballoon-suspendednettrapatS1andS2was20and10m
AGL,respectively.Theballoonswereloweredforsafetyto2mAGLbothduringthenight
(2100–0430hJST)andwhenthewindwasstrongoritrained.
Insectsinthe10-mor5-mnettraps,suctiontrapsandballoon-suspendednettrapsmen-
tionedabovewerecollectedat0430,0600,0800,1000,1200,1400,1600,1800,1900,2000,and
2100hJST,andthenumberoftrappedL.striatelluswascounted.ForthetrapsatS1andS2,
dataondayswhenthereweremissingdataduetostrongwind,heavyrain,andelectricpower
interruptionswereexcluded.
StatisticalanalysisoftheJapanesetrapdataconsistedofthreesteps.First,toavoidsparse
datafromthecatchnumberineachtimecategory,catchnumberdataoffemaleandmale
L.striatelluswerere-categorizedinto3timecategories,i.e.,timecategoryfrom0600to1200h
JST(Morning),at1400and1600hJST(Afternoon),andat1800and2000hJST(Evening).
Then,theoveralldifferencebetweenthecatchpatternoffemalesandmaleswasanalyzedbylo-
gisticregressionandlikelihoodratiotestswithtimes(Morning,Afternoon,Evening)nestedby
5differenttraps(the10-mnettrapatS1in2012,thesuctiontrapatS2in2012,the10-mnet
trapatS1in2013,the5-mnettrapatS1in2013,andthesuctiontrapatS1in2013).These
trapswereselectedbecausetheircatchnumberswerelarge,anddailycatchnumbers≧10were
usedforeachtrap.Inthesecondstepoftheanalysis,whenitwasevidentthattherewasnot
anysignificantdifferencebetweenfemalesandmales,thenumbersoffemaleandmalewere
summedforasimpleinsectcatchnumberwithineachoriginaltimecategory(0600,0800,
1000,1200,1400,1600,1800,and2000hJST)onadailybasis.Then,proportionaldataof
L.striatellus(sumofthenumberoffemalesandmalesineachtimecategory/dailytotalnum-
beroffemalesandmales)werearcsinetransformed,andanalyzedtodetermineoveralldiffer-
encesamongtheeighttimecategories(0600,0800,1000,1200,1400,1600,1800,and2000h
JST)andfivedifferenttrapsbyaGeneralLinearModel.Inthethirdstep,whentherewasasig-
nificantdifferenceamongthetimecategoriesand/ortrapsinthepreviousstep,differencesin
thearcsine-transformedproportiondatabetweenapairwisecombinationofthetimecategories
and/ortrapsweredeterminedbytheTukey-KramerHSDtest.Thesestatisticalanalyseswere
conductedwithJMP8software(SASInstituteInc.,Cary,NC,USA).
Thehelicopter-towednettrapconsistingofasquarepyramidofmeshfabricwasusedto
catchinsectsatanaltitudeasdescribedbyBeerwinkleetal.(1990)[30](Fig.2b).Theframeof
thenettrapwasmadeofsteelpipes(48.6mmindiameter,JISG3444STK500)andzincalloy
joints.Steelwires(9mmindiameter×10mlong)connectedthenettrapanda1-mbalance
(SupertoolCo.,Ltd.,LSBN11)thatwasattachedtoaloadhookonthehelicopter(Eurocopter,
AS350B).Thesizeofthesquareapertureoftheplasticmeshnetwas207×207cmandthe
depthwas226cm.Asmallmeshbagtocatchinsectswasattachedwithahookandloopfasten-
ertothesquaremeshtube(8×8×20cm)atthetailofthenet.Themeshbagandthemeshtube
wereclosedbytwoclippinggatesoneachsliderunit(OrientalMotorCo.,Ltd.,ELSM2-
XE020K),atailgateandafrontgate,beingcontrolledbyanoperatorinthehelicopter’scabin
withatabletcomputer(GoogleInc.Nexus7)throughawirelessLAN.Duringascentforasam-
plingflight,allthegateswereopen.Thetailgatewasclosedwhenthehelicopterreachedalevel
ofabout270mabovethegroundandsamplingatabout260mstarted.Duringthesampling,
thehelicoptermaintaineditsheightandflightspeed(65km/h)andfollowedanelliptical
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flight-path(3kmEW×1.7kmNS)for20min.Thecenteroftheflight-pathwaslocatedover
wheatfieldsabout3kmnorthofSagaAirport(33.150°N,130.302°E:7.7kmsouthofS1)
(Fig.1).Thefrontgatewasclosedwhenthesamplingended.Sixflightswithstartingtimesof
0718,0832,1031,1530,1647and1826hJSTonMay31,asunnyday,wereconducted.There
wasnorepetitiononanotherdayduetolimitedavailabilityofthehelicopter.
Theinsectscollectedbythenet,suction,balloon-supportedandhelicopter-towednettraps
werefrozeninarefrigeratorat-20°Candcountedwithinafewdaysafterthecollectionina
laboratoryattheSagaPrefecturalAgricultureResearchCenter.
Nilaparvatalugenstakesoffatanilluminanceofapproximately100lux[19],whereasthere
werenosuchreportsforL.striatellus.Hence,theilluminance(lux)atS2atduskanddawnwas
measuredin2012byanilluminancemeter(SanwaElectricInstrumentCo.,Ltd.,LX2)withthe
photosensorpointedupward.
Additionally,inordertodeterminewhetheranyoverseasimmigrantsarrivedintheJapa-
nesesurveyareaduringthetwo-yearsurveyperiod,simulatedmigrationfromJiangsuProvince
towesternJapanwasexaminedwithin24haftertakingoff.Inotherwords,thisanalysis
showedwhetherwindsfavorablefortheoverseasmigrationfromChinatowesternJapanoc-
curred.Themigrationsimulationwascalculatedusingthepredictionmethodreportedin
Otukaetal.(2012)[19],andamigrationdurationof24hwasacriterioninthemethod.Inad-
dition,thenumberofinsectstrappedinanoperational10-mnettrapattheNagasakiPlant
ProtectionStation,IsahayaCity,NagasakiPrefecture(32.837°Nand130.021°E,2mASL)
(Fig.1),locatedapproximately50kmsouthwestoftheS1site,wasusedtodetermineifany
overseasimmigrantsweretrappedthere.ThenettrapwaslocatedinthewesternpartofKyu-
shuIskand,whichisasensitiveplacetocatchtheinsect’soverseasimmigration.Thissurvey
wasconductedbytheNagasakiPlantProtectionStationinaregularmonitoringprogram.No
specialpermissionwasneededforthissurveybecausethesiteisnotlocatedinanyprotected
areaandnoprotectedspeciesweresampledinthesurvey
Results
Chinesesurvey
ThedailynumberofL.striatelluscaughtinthenettrapatTongzhouin2012waslow,not
morethan13insects,untilJune7.Thecatchnumberpeakedat496onJune8,andthende-
creasedto317insectsonJune9,69onJune10,119onJune11,and7onJune12.Sinceinsects
werenotcollectedatallobservationtimesonJune10and11duetoheavyrains,complete
hourlycatchdatawereobtainedonlyonJune8and9(Fig.3a).Thenumberoftrappedinsects
peakedat1800hCST(Fig.3b),andthendecreasedquicklytoasmallnumberat2000hCST.
Althoughmorefemaleinsectsweretrappedthanmales(Fig.3c),thetemporalpatternsofboth
sexesweresimilar,andpeakedat1800hCST.SunsetatTongzhouonJune8,2012occurredat
1901hCST,anddusk,whentheilluminanceis100lux,shouldbeabout10minafterthistime.
Therewerealsosomecatchesduringthedaytime,from0900to1500hCST,butcatchesduring
thenight(from2100to0440hCST)anddawn(from0440to0700hCST)wererelatively
small.SunriseatTongzhouonJune8,2012occurredat0449hCST.
In2013,fewinsectsweretrappedincanopytrapsduringthenight,atdawnorintheearly
morning(1935–0700hCST);however,moreinsectsweretrappedduringthedayandevening
thanatothertimes(Fig.4).Thetotalnumberofinsectstrappedinthetwocanopytrapswas79
(female:40,male:39).Duringthedayandevening,0735–1900hCST,thenumberofL.striatel-
lusthatenteredthecanopytrapchangedhourly,butincreasedgraduallytowardstheevening
andpeakedat1700h(Fig.5a).Incanopytraps,thecatchpatternforfemalespeakedat1700h,
butthatformalespeakedat1900h(Fig.5b).
PLOSONE|DOI:10.1371/journal.pone.0120271 March17,2015 9/20
Take-OffTimeofLaodelphaxstriatellusinEastAsia
Fig3.ThenumberofL.striatellustrappedinthenettrapatTongzhou,JiangsuProvince,China.a.The
dailynumberofinsectstrapped.b.Thenumberofinsectstrappedatthree-hourintervalsonJune8and9,
2012.c.ThesexofinsectstrappedonJune8and9,2012asshownina.
doi:10.1371/journal.pone.0120271.g003
Japanesesurvey
Inthefieldsurvey,noL.striatelluswerecapturedat0430hJSTinthenettrapatS1in2012.
NoL.striatelluswerecapturedat0430hinthe10-mand5-mnettrapsatS1in2013.Twoand
oneL.striatelluswerecaughtat0430hinthesuctiontrapin2013atS1andS2,respectively.
NoL.striatelluswerecaughtbythelighttraps,exceptfortwospecimenscaughtatS1in2013.
PLOSONE|DOI:10.1371/journal.pone.0120271 March17,2015 10/20