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Evaluation of Predatory Mites and Acramite for Control of Twospotted Spider Mites in Strawberries in North Central Florida
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Title: Evaluation of Predatory Mites and Acramite for Control of Twospotted Spider Mites in Strawberries in North Central Florida
Series Title: J. Econ. Entomol. 99(4): 1291-1298 (2006)
Physical Description: Journal Article
Language: English
Creator: Rhodes, Elena M.
Liburd, Oscar E.
Publisher: Entomological Society of America
Publication Date: 2006
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Abstract: Greenhouse and field experiments were conducted from 2003 to 2005 to determine the effectiveness of two predatory mite species, Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor), and a reduced-risk miticide, Acramite 50 WP (bifenazate), for control of twospotted spider mite, Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). In greenhouse tests, three treatments consisting of releases of P. persimilis, N. californicus, and an untreated control were evaluated. Both species of predatory mites significantly reduced twospotted spider mite numbers below those found in the control during the first 3 wk of evaluation. However, during week 4, twospotted spider mite numbers on the plants treated with P. persimilis increased and did not differ significantly from the control. Field studies used releases of P. persimilis and N. californicus, applications of Acramite, and untreated control plots. Both N. californicus and P. persimilis significantly reduced populations of twospotted spider mite below numbers recorded in the control plots. During the 2003-2004 field season P. persimilis took longer than N. californicus to bring the twospotted spider mite population under control (<10 mites per leaflet). Acramite was effective in reducing twospotted spider mite populations below 10 mites per leaflet during the 2003-2004 field season but not during the 2004-2005 field season, possibly because of a late application. These findings indicate that N. californicus releases and properly timed Acramite applications are promising options for twospotted spider mite control in strawberries for growers in north Florida and other areas of the southeast.
Funding: Support for the development of the technical infrastructure and partner training provided by the United States Department of Education TICFIA program.
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Dina Benson.
Publication Status: Published
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Rights Management: Permissions granted to the University of Florida Institutional Repository and University of Florida Digital Collections to allow use by the submitter. Open access rights reserved by the authors.
System ID: IR00000081:00001

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HORTICULTURALENTOMOLOGYEvaluationofPredatoryMitesandAcramiteforControlofTwospotted SpiderMitesinStrawberriesinNorthCentralFloridaELENAM.RHODESANDOSCARE.LIBURDDepartmentofEntomologyandNematology,UniversityofFlorida,Gainesville,FL32611 J.Econ.Entomol.99(4):12911298(2006)ABSTRACT Greenhouseandeldexperimentswereconductedfrom2003to2005todeterminethe effectivenessoftwopredatorymitespecies, Phytoseiuluspersimilis Athias-Henriotand Neoseiulus californicus (McGregor),andareduced-riskmiticide,Acramite50WP(bifenazate),forcontrolof twospottedspidermite, Tetranychusurticae Koch,instrawberries( Fragariaxananassa Duchesne).In greenhousetests,threetreatmentsconsistingofreleasesof P persimilis N californicus ,andan untreatedcontrolwereevaluated.Bothspeciesofpredatorymitessignicantlyreducedtwospotted spidermitenumbersbelowthosefoundinthecontrolduringtherst3wkofevaluation.However, duringweek4,twospottedspidermitenumbersontheplantstreatedwith P persimilis increasedand didnotdiffersignicantlyfromthecontrol.Fieldstudiesusedreleasesof P persimilis and N californicus ,applicationsofAcramite,anduntreatedcontrolplots.Both N californicus and P persimilis signicantlyreducedpopulationsoftwospottedspidermitebelownumbersrecordedinthecontrol plots.Duringthe20032004eldseason P persimilis tooklongerthan N californicus tobringthe twospottedspidermitepopulationundercontrol( 10mitesperleaet).Acramitewaseffectivein reducingtwospottedspidermitepopulationsbelow10mitesperleaetduringthe20032004eld seasonbutnotduringthe20042005eldseason,possiblybecauseofalateapplication.Thesendings indicatethat N californicus releasesandproperlytimedAcramiteapplicationsarepromisingoptions fortwospottedspidermitecontrolinstrawberriesforgrowersinnorthFloridaandotherareasofthe southeast. KEYWORDS Acramite, Neoseiuluscalifornicus Phytoseiuluspersimilis ,twospottedspidermite, strawberry Thetwospottedspidermite, Tetranychusurticae Koch, isthekeyarthropodpestaffectingstrawberries( Fragariaxananassa Duchesne)inFlorida(Mosslerand Nesheim2003).Theirfeedingcausesinjurytochlorophyllcontainingmesophyllcellswithintheleaftissue,whichresultsinadecreaseofphotosynthetic capacitiesofinfestedleaves(Sancesetal.1982).Early seasoninfestationsoftwospottedspidermitescause reductionsinphotosynthesisandtranspirationata muchlowerpopulationlevelthanthepopulationlevel thatcausesthesamelevelofinjurylaterintheseason (Sancesetal.1981). Developmentfromeggtomatureadulttakes 19d (Mitchell1973),althoughthistimecanbeasshortas 5d(HoandLo1979).Optimalconditionsfordevelopmentarehightemperatures(upto38 C)andlow humidity(WhiteandLiburd2005).Theirhighfecundityandshortlifecycleallowtwospottedspidermites toquicklybecomeresistanttomiticidesusedtocontrolthem.Theuseofreduced-riskmiticidesandperiodicreleasesofpredatorymitesmaygivegrowers moreoptionsformanagementoftwospottedspider mites. Acramite50WP(bifenazate)(Crompton,Morgantown,WV)isareduced-riskmiticidethathasshown promisingresultsinstrawberries(Liburdetal.2003). Thismiticidehasalowtoxicitytowardpredatorymites (White2004).Acramitecanonlybeappliedtwicein aseasonat0.851.125kgofproductperhectarewith applicationsatleast21dapart(Price2002,Mossler andNesheim2003).Inlaboratorystudiesusingleaf disks,White(2004)recordedahigherrateoftwospottedspidermitemortalityusingAcramite50WPcomparedwiththeconventionalmiticideVendex(fenbutatinoxide)(DuPont,Wilmington,DE). Phytoseiuluspersimilis Athias-Henriotand Neoseiuluscalifornicus (McGregor)arepredatorymitesbelongingtothefamilyPhytoseiidae.Theyhavebeen showntoeffectivelycontroltwospottedspidermites onstrawberryandothercropsinvariouspartsofthe world(PortandScopes1981,Cross1984,Charlesetal. 1985,Charles1988,Waite1988,Easterbrook1992,Decou1994,Crossetal.1996,Garcia-MariandGonzalezZamora1999,Easterbrooketal.2001,Barberetal. 2003,Liburdetal.2003). Phytoseiuluspersimilis and N. californicus arealsoeffectiveincontrollingtwospottedspidermitesonstrawberriesinCalifornia(Oat-0022-0493/06/12911298$04.00/0 2006EntomologicalSocietyofAmerica

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manetal.1967,1968,1976,1977a,b;Trumbleand Morse1993). Phytoseiuluspersimilis isatypeIspecialistthatfeedsexclusivelyon Tetranychus mites (McMurtryandCroft1997).Incontrast, N.californicus hastraitsofbothatypeIIspecialistandatypeIII generalist(Croftetal.1998). N.californicus prefer spidermitesasfoodbutcansubsistonothersources offoodsuchasthripsandpollenwhenmitepopulationsarelow,andtheyalsopreyuponotherpredatory mitespecies(Gersonetal.2003). InFlorida,seasonalreleasesof P.persimilis have beenfairlysuccessfulincontrollingtwospottedspider mitepopulationsinthesouthernregionsofthestate (Decou1994).However,releasesof P.persimilis have notbeeneffectiveinnorthernFlorida,possiblybecauseitmaynotbeabletosurvivethewintertypical ofthisarea(White2004).Preliminarystudiesby Liburdetal.(2003)indicatethat N.californicus may beabletoeffectivelycontroltwospottedspidermite innorthFloridastrawberrieswhere P.persimilis is ineffective. Theobjectiveoftheseexperimentswastocompare theefcacyofbothspeciesofpredatorymitesfor controloftwospottedspidermitesundercontrolled greenhouseconditionsandundereldconditionsin northFlorida.Undercontrolledgreenhouseconditions, P.persimilis wouldbeexpectedtoperformas wellasorbetterthan N.californicus becausetemperatureeffectsarenotafactor. Intheeld,ourhypothesiswasthat N.californicus wouldprovidebettercontroloftwospottedspider mitescomparedwith P.persimilis. Furthermore,both N.californicus andAcramitewouldsignicantlyreducepopulationsoftwospottedspidermitesinstrawberriestobelowlevelsfoundinuntreated(control) plots. MaterialsandMethods Colony. Atwospottedspidermitecolonyrearedon strawberrieswasmaintainedinthelaboratorytoensurethatonlytwospottedspidermitespredisposedto strawberrieswereusedintheexperiments.Thecolonyconsistedofmite-infestedstrawberryplantsthat werekeptunderaphotoperiodof14:10(L:D)regime atatemperatureof 27 Cwith65%RH.Plantswere wateredtwiceweekly. PredatorymitesusedinallexperimentswereobtainedfromKoppertBiologicalSystems(Romulus, MI).Predatorymiteswereusedwithin48hoftheir arrivaldates. GreenhouseExperiment. Fifteenmite-freeFestival'strawberryplantswithatotaloffourtrifoliates wereplacedintopreviouslyconstructedmite-free cages(Fig.1).Eachplantwasplacedintoanindividual cage(60by30by20cm).Cageswereconstructedof nylonfabric.Velcrowasplacedonthreesidesofthe cagetogaineasyaccesstotheplants.Eachcagewas attachedtoapotcontainingastrawberryplantby usingapullcordsownintothebottomofthecage. Cageswereusedtokeepbothtwospottedspidermites andpredatorymitesfromdispersingbetweenplants. Tentwospottedspidermiteswerereleasedontoeach plantandallowedtomultiplyfor1to2wk(thisvaried dependingonwhenthepredatorymiteshipmentarrived).Beforethereleaseofpredatorymites,aleaet wascollectedfromeachplant.Thenumberof twospottedspidermitemotilesandeggsoneachleafletwascounted,andthemeannumberperleaetwas calculated.Theaveragereleaseratewasapproximatelya10:1ratio(10twospottedspidermitetoone predatorymite).Also,arepresentativesample(one bottlefromeachspeciesofpredatorymite)wasobservedforatleast15mintoensurethattheshipped predatorymiteswereactiveandingoodcondition beforeuse. Experimentaldesignwasacompletelyrandomized blockwiththreetreatments.Eachtreatmentwasreplicatedvetimes.Treatmentsincluded1)10 P.persimilis adultsreleasedperinfestedplant( 100 twospottedspidermites),2)10 N.californicus adults releasedperinfestedplant( 100twospottedspider mites),and3)untreated(control)plants( 100 twospottedspidermites)withoutpredatorymites. Sampling. Eachweekthepopulationofpredators andtwospottedspidermiteswassampledbytaking oneleaetfromeachplant(veleaetsfromeach individualtreatment)andcountingthenumbersof twospottedspidermitesaswellaspredatorymites (motilesandeggs).Thetermmotilesreferstoalllife stagesexcepteggs.Sampleswererecordedfor4wk. Threetrialsofthisexperimentwererun:thersttrial wasconductedinFebruary/March2004,thesecondin December2004/January2005,andthethirdinMarch/ April2005. DataAnalysis. Twospottedspidermitemotileand eggdatawerelogtransformed.Meantwospottedspidermitesperleaetwascomparedeachweekacross treatmentsbyusingananalysisofvariance(ANOVA), andmeanswereseparatedusingaleastsignicant difference(LSD)test(SASInstitute2002). Fig.1. Mite-freecages(60by30by20cm)containing strawberryplants.1292JOURNALOFECONOMICENTOMOLOGYVol.99,no.4

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FieldExperiment. TheeldexperimentwasconductedattheUniversityofFlorida,PlantScience ResearchUnit,Citra,FL.Festivalstrawberryplants wereplantedinmid-October.Theyweregrownasan annualcroponraisedbedscoveredbyblackplastic mulch.Acombinationofoverheadanddripirrigation wasusedfortherst3wktohelpestablishthetransplants.Afterthisestablishmentperiod,onlydripirrigationwasused.Strawberrieswereplantedinplots7.3 by6.1mconsistingofsixrows0.5mwidewith0.5-m rowspacing.Therewere24plotsarrangedi na4by6 gridandspaced7.3mapart.Theexperimentwasa completelyrandomizedblockdesignwithsixreplicates.Fourtreatmentswereevaluatedandincluded1) tworeleasesof P.persimilis (P),2)tworeleasesof N. californicus (N),3)twoapplicationsofthereducedriskmiticideAcramite50WPattherateof1.125kgof productperhectare(A),and4)anuntreatedcontrol (C).Inthe20032004eldseason,alltreatmentswere appliedduringtheweeksof11Decemberand11 February.Inthe20042005eldseason,alltreatments wereappliedon9Decemberandagainon10March. Predatorymiteswereappliedatarateofonebottle (2000mites)perplotbyhandbygentlyrotatingthe bottleovereachplant.Acramitewassprayedusinga 11-liter(3-gal)backpacksprayer. Sampling. Samplingwasinitiatedoncetheplants hadestablished( 3wkafterplanting).Eachweek,six leavesperplot(36leavespertreatment)werecollectedrandomlyfromthemiddleandlowerstrataof eachplantandbroughtbacktothelaboratorywhere thenumberoftwospottedspidermitemotilesand eggsandpredatorymitemotilesandeggsoneachleaf werecountedunderadissectingmicroscope.Only P. persimilis and N.californicus miteswerecounted. DataAnalysis. Thetwospottedspidermitemotile andeggdatawereseparatedintoveperiodsbasedon treatmentapplicationdatesandtimeduringtheseason.Thiswasalsoimportanttoexaminetrends throughoutthe4-moeldseason.Theseperiodswere 1)pretreatment(3wkbeforeanytreatment),2)early-season(posttreatmenttoweek7),3)mid-season (week8towhenthesecondapplicationwasapplied in20032004atweek12),4)early-lateseason(week 13towhenthesecondtreatmentwasappliedinthe 20042005seasonatweek16),and5)lateseason (weeks1719).Thelateseasonwassplitintotwo periodsbecauseofthedifferenceintimingofthe secondapplicationbetweenseasons.Forexample, duringthe20032004season,thesecondapplication occurredatthebeginningofthelateseason,whereas inthe20042005eldseason,thesecondapplication occurredinthemiddleofthelateseason.Ineach period,datawerelogtransformedandthentreatments werecomparedusinganANOVA,andmeanswere separatedusinganLSDtest(SASInstitute2002). Yield. Yielddatawerecollectedbeginninginearly Januaryinbothseasons.Strawberrieswereharvested weeklybyhand.Marketablestrawberriesfromthe fourinnerrowswereweighedonabenchscale(MettlerToledo,Columbus,OH).Damaged,rotten,and severelydeformedstrawberrieswerediscarded.The twoouterrowsservedasborderrowsandthestrawberriesfromtheserowsalsowerediscarded. DataAnalysis. Themeanyieldpertreatmentfor thewholeseasonwascomparedacrosstreatments usinganANOVA(SASInstitute2002).ALSDtestwas usedtoshowtreatmentdifferencesfortheyielddata. Thiswasdoneforbotheldseasons. Results GreenhouseExperiment. Therewerenosignicant differencesintwospottedspidermitemotileandegg populationsamongtreatmentswhentheinitialsample wastaken(week0)(motiles: F 1.1;df 2,24; P 0.3638;eggs: F 0.94;df 2,24; P 0.4046)and1wk afterpredatorymiterelease(motiles: F 0.08;df 2, 24; P 0.9257;eggs: F 0.45;df 2,24; P 0.6441) (Fig.2).Twoweeksafterthereleaseofpredatory mites, P.persimilis signicantlyreducedtwospotted spidermitemotileandeggnumbersbelownumbersin thecontrol(motiles: F 3.4;df 2,24; P 0.0513; eggs: F 4.4;df 2,24; P 0.0230).However, twospottedspidermitenumbersonplantswhere N. californicus wasreleasedwereintermediate,averaging Fig.2. Weeklymean SEMtwospottedspidermite (TSSM)(a)motilesand(b)eggsperleaetineachtreatmentinthegreenhouseexperiment.Week0istheinitial sampletakenbeforepredatorymiteswerereleased.Means onthesamedatefollowedbythesameletterarenotsignificantlydifferentbyLSD( P 0.05)(C,control;P, P persimilis ;andN, N californicus ).August2006RHODESANDLIBURD:CONTROLOFTWOSPOTTEDSPIDERMITES1293

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1.3 1.3motilesand9.7 8.4eggsperleaet(Fig.2). Bothspeciesofpredatorymitessignicantlyreduced numbersoftwospottedspidermitemotilesandeggs belowthecontrolbyweek3(motiles: F 6.2;df 2, 24; P 0.0068;eggs: F 6.0;df 2,24; P 0.0075). Twospottedspidermitemotileandeggnumberson plantswhere P.persimilis werereleasedbegantoincreaseatweek4andwerenotsignicantlydifferent fromthecontrol.Atthistime,thereweresignicantly fewermotilesperleaetinthe N.californicus treatmentcomparedwiththeothertwotreatments(motiles: F 4.3;df 2,24; P 0.0256).However,the differenceineggnumberswasnotsignicant(eggs: F 1.9;df 2,24; P 0.1717). Oneweekafterpredatorymiterelease,therewere anaverageof0.1 0.1 P.persimilis motilesperleaet inthe P.persimilis treatment.Thisincreasedto0.5 0.2motilesperleaetatweek2and0.7 0.6motiles perleaetatweek3.Thepopulationthendecreased to0.3 0.2motilesperleaetatweek4.Onlyone P. persimilis eggwasrecordedinthestudyatweek4in thethirdtrialoftheexperiment. Incontrast, N.californicus numbersinthe N.californicus treatmentweresimilarthroughoutthestudy. Therewereanaverageof0.7 0.5,0.7 0.4,0.6 0.3, and0.6 0.3motilesperleaetatweeks1,2,3,and 4,respectively.Intotal,seveneggswerelaidduring theexperiment:fouratweek1inthersttrial,oneat week2inthethirdtrial,andtwoatweek3inthe secondtrial. FieldExperiment. 20032004FieldSeason. There werenosignicantdifferencesinmotileandeggnumbersamongtreatmentsinthepretreatmentperiod (motiles: F 0.8;df 3,15; P 0.5041;eggs: F 0.7; df 3,15; P 0.5805)orintheearly-season(motiles: F 0.7;df 3,15; P 0.5511;eggs: F 1.4;df 3, 15; P 0.2755)(Fig.3).The N.californicus andAcramitetreatmentshadsignicantlyfewermotilesand eggsperleaetthanthecontrolplotsduringthemidseason(motiles: F 3.9;df 3,15; P 0.0297;eggs: F 5.0;df 3,15; P 0.0137)andduringtheearly-late season(motiles: F 5.1;df 3,15; P 0.0121;eggs: F 4.0;df 3,15; P 0.0280)(Fig.3).Duringthese twoperiods,twospottedspidermitenumbersinthe P. persimilis treatmentwerefairlyhighbutwerenot signicantlydifferentfromtwospottedspidermite numbersinthe N.californicus treatment.Also,numbersoftwospottedspidermiteinthe P.persimilis treatmentwerenotsignicantlydifferentfromthose inthecontrolwiththeexceptionoftheearly-late seasonintermsofthenumbersofmotiles(Fig.3). Therewerenosignicantdifferencesintwospotted spidermitemotileandeggnumbersamongtreatments inthelateseason(motiles: F 1.2;df 3,15; P 0.3461;eggs: F 0.68;df 3,15; P 0.5777). Predatorymiteswereobservedfrom17December until17March(mid-andearly-lateseasons).Inthe P. persimilis treatment,the P.persimilis populationbeganincreasingon7Januaryreachingapeakof1.4 0.4motilesand1.6 0.4eggsperleaeton20January. Thepopulationremainedhighforseveralweeksthen declinedsharplyon20Februaryandremainedlow. No P.persimilis wererecordedafter17March.Inthe N.californicus treatment,the N.californicus populationbegantoincreaseat17December,reachinga peakof1.0 0.3motilesand0.6 0.1eggsperleaet on2February.Thepopulationdeclinedsharplyat25 February.Afterthisdate,no N.californicus wererecordedwiththeexceptionofasmallnumbernotedon 30March(notwospottedspidermiteswererecorded after25Februaryinthistreatmenteither).Verysmall numbersofmotilesofbothspecieswererecorded fromtheAcramitetreatmenttheweekaftereach release.However,noeggswereeverrecorded.Small numbersofbothspeciesdispersedintothecontrol plotsandwererecordedfrom2Februaryuntil9 March.Thecombinedpopulationneverexceeded 0.4 0.3motilesor0.2 0.2eggsperleaet. 20042005FieldSeason. Duringthe20042005eld season,thetwospottedspidermitepopulationpeaked muchlaterintheseason.Therewerenosignicant differencesintwospottedspidermitemotileandegg numbersinthepretreatmentperiod(motiles: F 0; df 3,15; P 1;eggs: F 0;df 3,15; P 1)orin theearly-season(motiles: F 0.47;df 3,15; P 0.7073;eggs: F 0.57;df 3,15; P 0.6432)(Fig.4). Fig.3. Mean SEMtwospottedspidermite(TSSM)(a) motilesand(b)eggsperleaetforveperiodsofthe2003 2004eldseason.Meansonthesamedatefollowedbythe sameletterarenotsignicantlydifferentbyLSD( P 0.05) (C,control;P, P persimilis ;N, N californicus ;A,Acramite).1294JOURNALOFECONOMICENTOMOLOGYVol.99,no.4

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Therewerealsonosignicantdifferencesintwospottedspidermitemotileoreggnumbersinthemidseason(motiles: F 1.9;df 3,15; P 0.1699;eggs: F 2.4;df 3,15; P 0.1129).However,twospotted spidermiteeggnumbersshowedatrendofbeing higherintheAcramitetreatmentcomparedwiththe N.californicus treatmentduringthemid-season(Fig. 4).Thecontroltreatmenthadsignicantlyhigher numbersoftwospottedspidermitemotilesandeggs thanthe N.californicus and P.persimilis treatmentsin theearly-lateseason(motiles: F 11.1;df 3,15; P 0.0004;eggs: F 13.0;df 3,15; P 0.0002)and thelateseason(motiles: F 14.6;df 3,15; P 0.0001; eggs: F 14.6;df 3,15; P 0.0001)(Fig.4).During theearly-lateseason,numbersoftwospottedspider mitemotilesintheAcramitetreatmentdidnotdiffer signicantlyfromthosefoundinthecontrol.However,thereweresignicantlylesstwospottedspider miteeggsintheAcramitetreatmentduringthisperiod thaninthecontrol.TheAcramitetreatmenthadsignicantlyhighernumbersoftwospottedspidermite motilesandeggsthanbothpredatorymitetreatments intheearlylateseason.Inthelateseason,theAcramitetreatmenthadsignicantlymoretwospotted spidermitemotilesthanbothpredatorymitetreatmentsandsignicantlymoretwospottedspidermite eggsthanthe N.californicus treatment(Fig.4). Predatorymiteswereobservedfrom12January until30March(mid,early-late,andlateseasons). Observationsweresporadicuntil23February.Inthe P.persimilis treatment, P.persimilis motilesandeggs wererecordedcontinuouslyfrom9Marchuntil30 March.Thepopulationneverroseabove0.1 0.1 motilesor0.1 0.03eggsperleaet.Inthe N.californicus treatment, N.californicus motilesandeggs wererecordedcontinuouslyfrom23Februaryuntil25 March.Thepopulationneverroseabove0.2 0.1 motilesor0.3 0.1eggsperleaet.Intotal,two P. persimilis motilesandfour P.persimilis eggswere recordedintheAcramitetreatmenton25March,and oneeggwasrecordedon16March.Bothspecies dispersedintothecontrolplotsandwererecorded from23Februaryuntil30March.Thecombinedpopulationreachedapeakof0.4 0.1motilesand0.4 0.1eggsperleaeton25Marchandthendeclined slightlyby30March. Yield. Inthe20032004season,themeantotalmarketableyieldfromthe P.persimilis treatmentwasnot signicantlydifferentfromthecontrol(Table1).The totalmarketableyieldforthe N.californicus treatment averagedsignicantlyhigherthanthe P.persimilis and controltreatments( F 3.36;df 3,15; P 0.0376). ThetotalmarketableyieldfortheAcramitetreatment wasnotsignicantlydifferentfromtheotherthree treatments. Incontrast,inthe20042005season,therewereno signicantdifferencesinmeantotalmarketableyield betweenthefourtreatments( F 2.6;df 3,15; P 0.0907)(Table1).Meantotalmarketableyieldper treatmentwasmuchlowerthanthepreviousseason. Marketableyieldsaveragedbetween35and40kgper treatmentcomparedwith8590kgpertreatmentin the20032004eldseason. Discussion GreenhouseExperiment. Ourresultsindicatethat bothspeciesofpredatorymitessignicantlyreduced twospottedspidermitenumbersbelowthosefoundin thecontrol. N.californicus suppressedtwospottedspidermitepopulationsforalongertimeperiodandits populationremainedrelativelyconstantthroughout theexperiment.However,thesepredatorsinitially Fig.4. Mean SEMtwospottedspidermite(TSSM)(a) motilesand(b)eggsperleaetforveperiodsofthe2004 2005eldseason.Meansonthesamedatefollowedbythe sameletterarenotsignicantlydifferentbyLSD( P 0.05) (C,control;P, P persimilis ;N, N californicus ;andA,Acramite).Table1.Meantotalmarketablestrawberryyieldfromeach treatmentforthe2003–2004and2004–2005eldseason Treatment Mean SEMtotalyield(kg)of strawberries 2003200420042005 Acramite93.9 4.9ab39.2 1.8 N.californicus 98.3 3.8a35.1 1.4 P.persimilis 83.1 4.8b37.2 0.9 Control83.1 7.6b38.9 1.1 Meanswithinaseasonfollowedbythesameletterarenotsignificantlydifferent(LSDtest; P 0.05).August2006RHODESANDLIBURD:CONTROLOFTWOSPOTTEDSPIDERMITES1295

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tooklonger(1wk)than P.persimilis toreduce twospottedspidermitenumbersbelowthecontrol. Thiswasnotsurprisingbecause P.persimilis isknown toquicklyknockdowntwospottedspidermitepopulationsundercontrolledconditions(Gilstrapand Friese1985).Inourstudies, P.persimilis seemstobe unabletosustainsuppressionoftwospottedspider mitebeyond3wkinthegreenhouse.Thetwospotted spidermitepopulationincreasedatweek4,whereas the P.persimiils populationdeclined.Thereasonfor thismayberelatedtoitsbiology.AsatypeIspecialist, P.persimilis cannotsurviveinareaswhereitsfood suppliesarelow.Therefore,oncethetwospottedspidermitepopulationhasbeengreatlyreduced, P.persimilis mustdispersetoanewlocationtondfood (McMurtryandCroft1997).Bothspeciesofpredatory miteslaidveryfeweggs.Wedonotknowwhythis occurred,butwespeculatethattherewasnotenough twospottedspidermitepreyforeitherspeciestoproducelargenumbersofeggs. FieldExperiment. Inbotheldseasons,therewere fewertwospottedspidermitesinthe N.californicus treatedplotscomparedwiththe P.persimilis -treated plots,althoughthedifferenceinthe20042005season wasnotsignicant.Thissuggeststhat N.californicus maybebetteratreducingorregulatingeldpopulationsoftwospottedspidermitethan P.persimilis. In thisstudy,wedonotthinkthatenvironmentalconditionscontributedtothebetterperformanceof N. californicus becausesimilarresultswereobtainedin thegreenhouseundercontrolledconditions. Acramitewashighlyeffectiveinthe20032004season,butdidnotadequatelycontroltwospottedspider mitepopulationsinthe20042005season.Thiswas primarilyaresultoftiming.Inthe20032004season, therstsprayknockeddownthetwospottedspider mitepopulationandthesecondsprayinearlyFebruarykeptthenumberslow.Duringthe20042005 season,incontrast,therewerenodetectabletwospottedspidermitepopulationswhenAcramitewasrst sprayed.Bythetimetwospottedspidermitepopulationsbegantoincrease,therewaslittleresidualactivityleftintheAcramiteplots.WedelayedthesecondapplicationofalltreatmentsuntilMarchduring the20042005eldseasonsothattwospottedspider mitepopulationscouldhaveachancetoincrease. BecausetheAcramiteplotswereessentiallycontrols (becauseofdelayedapplication),thetwospottedspidermitepopulationintheseplotsexplodedandwasso highthatthesecondapplicationofAcramitecouldnot signicantlyreducetwospottedspidermitelevels. ThisillustratestheimportanceofproperlytimingAcramiteapplicationsforgrowers.UsingAcramitein combinationwithothermanagementtactics(predatorymites)tocontroltwospottedspidermitesmight avoidsuchproblems,althoughfurtherresearchwould beneededtodemonstratethispossibility. Therewereseveraldifferencesinthetwospotted spidermitepopulationsbetweenthetwoeldseasons. Inthe20032004season,twospottedspidermiteswere presentintheplotsfromthestartoftheexperiment, theybegantoincreasewhenthetemperaturebegan toincrease,andthendeclinedbythelastfewweeks oftheseason.Incontrast,nodetectablenumbersof twospottedspidermiteswerefoundinthe20042005 seasonuntilmid-January,andthenumbersoftwospottedspidermitedidnotincreasegreatlyuntillate February.Overall,bothtwospottedspidermiteand predatorymitenumbersweremuchlowerinthe 20042005season.WhiteandLiburd(2005)found thattwospottedspidermitespreferhot,dryconditions,andthelatesummerandfall2004wereincrediblywetbecauseofhurricanesFrancisandJeanne. Thismayhaveknockedbackthesurroundingpopulationoftwospottedspidermites,leavingsmallernumberstodisperseintothestrawberrieswhentheywere planted. Anotherdifferenceinthetwospottedspidermite populationsbetweenseasonswasthatthepresenceof thegreenformoftwospottedspidermitewasmuch moreprevalentthantheredformin20032004.This trendreverseditselfin20042005.Theredandgreen formswereconsideredseparatespeciesuntilHinomotoetal.(2001)showedthatreproductiveincompatibilitybetweenthetwoformsisincomplete.Using cytochromeoxidasesubunitIsequences,Hinomotoet al.(2001)demonstratedthatthetwoformsbelongto thesamespeciesfromaphylogeneticstandpoint.We donotknowwhythegreenformpredominatedin 20032004andtheredpredominatedin20042005. Thiswouldbeaninterestingtopictoresearchfurther. Predatorymitepopulationtrendsalsodiffered greatlybetweenseasons.In20032004,bothspecies wereabundantwhentwospottedspidermitepopulationswerehigh,decliningwhenpreypopulationsdiminished.In20042005,predatorymitesalsowere presentwhentwospottedspidermitepopulations werehigh(comparedwiththerestoftheseason). However,overallpredatorymitepopulationswere muchlowerthanthoseinthepreviousseason.This wasprobablybecauseoftheoverallmuchlower twospottedspidermitepopulationinthe20042005 season. Yield. Duringthe20032004eldseason,the N. californicus treatmenthadasignicantlyhighermean totalmarketableyieldthanboththecontroland P. persimilis treatments.However,duringthe20042005 eldseason,therewerenosignicantdifferences amongtreatments.Thedifferenceintwospottedspidermitepopulationtrendsbetweenthetwoseasons maypartiallyexplainwhythereweresignicantdifferencesbetweentreatmentsin20032004butnotin 20042005.Sancesetal.(1981)foundthathigher numbersoftwospottedspidermitesareneededto causeasimilarlevelofdamagewheninfestationoccurslaterintheseason.Thatthetwospottedspider mitepopulationin20042005wassolowandtwospottedspidermitesoccurredsolateintheseasonsuggestedthatthenumbersoftwospottedspidermites werenothighenoughtoaffectthequantityofstrawberriesproducedduringthe20042005eldseason. Otherfactorsthatmayhavecontributedtothelackof signicantdifferencesinthe20042005eldseason wereagreateramountoffungalproblems,including 1296JOURNALOFECONOMICENTOMOLOGYVol.99,no.4

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Anthracnosefruitrot, Colletotrichumacutatum Simmonds,andgray,mold Botrytiscinerea Pers;birddamage;andweedinfestationin20042005.Thesefactors alsomayhaveleadtotheoveralllowermarketable yieldsin20042005comparedwith20032004. Overall,releasesof N.californicus seemtobea viabletacticfornorthFloridastrawberrygrowers. Acramiteisveryeffectiveifapplicationsaretimedand appliedproperly.ApplicationofAcramitefollowedby thereleaseofaneffectivepredatorymitesuchas N. californicus maybeaneffectivemanagementtacticfor strawberrygrowersinnorthFlorida.Furtherresearch oncombinationtreatmentsisneededbeforedenite conclusionscanbedrawn. AcknowledgmentsWethankScottTaylorandthestaffattheCitraPlant ScienceResearchandEducationUnitlocatedinCitra,FL, forassistanceinmanagingourresearchplots.Wealsothank AlejandoArevalo,MarinelaCapana,andRaymondLittellfor helpwiththestatisticalanalysis.Finally,wethankallthestaff andstudentsoftheUniversityofFloridaSmallFruitand VegetableIntegratedPestManagementLaboratoryin GainesvilleFlorida,especiallyCrystalKelts,forassistancein theeldwork.WethankRobertMeagherandDonaldDicksonforeditingtheearlierdraftsofthismanuscript.Funding forthisprojectwasprovidedbyanEPARegionfourStrawberryIPMGrant736404813.ReferencesCitedBarber,A.,C.A.M.Campbell,H.Crane,R.Lilley,andE. Tregidga.2003. Biocontroloftwo-spottedspidermite Tetranychusurticae ondwarfhopsbythephytoseiidmites Phytoseiuluspersimilis and Neoseiuluscalifornicus. BiocontrolSci.Technol.13:275284. Charles,J.G.1988. Using Phytoseiuluspersimilis tocontrol two-spottedmitesinstrawberry,pp.202206. In Proceedingsofthe41stNewZealandWeedandPestControl Conference. Charles,J.G.,E.Collyer,andV.White.1985. Integrated controlof Tetranychusurticae with Phytoseiuluspersimilis and Stethorusbidus incommercialraspberrygardens.N ZJ.Exp.Agric.13:385393. Croft,B.A.,L.N.Monetti,andP.D.Pratt.1998. Comparativelifehistoriesandpredationtypes:are Neoseiulus californicus and N.fallacis (Acari:Phytoseiidae)similar typeIIselectivepredatorsofspidermites.Environ.Entomol.27:531538. Cross,J.V.1984. Biologicalcontroloftwo-spottedspider mite( Tetranychusurticae )by Phytoseiuluspersimilis on strawberriesgrowninwalk-in'plastictunnels,anda simpliedmethodofspidermitepopulationassessment. PlantPathol.33:417423. Cross,J.V.,C.M.Burgess,andG.R.Hanks.1996. Integratinginsecticideusewithbiologicalcontroloftwospotted spidermite( Tetranychusurticae )by Phytoseiuluspersimilis onstrawberryintheUK,pp.899906.BrightonCrop ProtectionConference-PestsandDiseases,1821November1996,Brighton,UnitedKingdom. Decou,G.C.1994. 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Thepredatorypotentialof Phytoseiuluspersimilis,Amblyseiuscalifornicus, and Metaseiulusoccidentalis (Acarina:Phytoseiidae).Int. J.Acarol.11:163168. Hinomoto,N.,M.Osakabe,T.Gotoh,andA.Takafuji.2001. Phylogeneticanalysisofgreenandredformsofthetwospottedspidermite, Tetranychusurticae Koch(Acari: Tetranychidae),inJapan,basedonmitochondrialcytochromeoxidasesubunitIsequences.Appl.Entomol. Zool.36:459464. Ho,C.C.,andK.C.Lo.1979. Inuenceoftemperatureon lifehistoryandpopulationparametersof Tetranychus urticae. Agric.Res.China.28:261271. Liburd,O.E.,G.G.Seferina,andD.A.Dinkins.2003. Suppressionoftwospottedspidermites.Universityof Florida.InstituteofFoodandAgriculturalSciencesExt. Newsl.Berry/VegetableTimes3:34. McMurtry,J.A.,andB.A.Croft.1997. Life-stylesofphytoseiidmitesandtheirrolesinbiologicalcontrol.Annu. Rev.Entomol.42:291321. Mitchell,R.1973. Growthandpopulationdynamicsofa spidermite( Tetranychusurticae K.,Acarina:Tetranychidae).Ecology54:13491355. Mossler,M.A.,andO.N.Nesheim.2003. Strawberrypest managementstrategicplan.Valrico,FL.Universityof FloridaIFASExtension,Gainesville,FL. Oatman,E.R.,F.E.Gilstrap,andV.Voth.1976. Effectof differentreleaseratesof Phytoseiuluspersimilis (Acarina: Phytoseiidae)onthetwospottedspidermiteonstrawberryinsouthernCalifornia.Entomophaga21:269273. Oatman,E.R.,J.A.McMurtry,F.E.Gilstrap,andV.Voth. 1977a. Effectof Amblyseiuscalifornicus,Phytoseiuluspersimilis, and Typhlodromusoccidentalsi onthetwospotted spidermiteonstrawberryinsouthernCalifornia.J.Econ. Entomol.70:4547. Oatman,E.R.,J.A.McMurtry,F.E.Gilstrap,andV.Voth. 1977b. Effectofreleasesof Amblyseiuscalifornicus onthe twospottedspidermiteonstrawberryinsouthernCalifornia.J.Econ.Entomol.70:638640. Oatman,E.R.,J.A.McMurtry,H.H.Shorey,andV.Voth. 1967. Studiesonintegrating Phytoseiuluspersimilis releases,chemicalapplications,culturalmanipulations,and naturalpredationforcontrolofthetwo-spottedspider miteonstrawberryinsouthernCalifornia.J.Econ.Entomol.60:13441351. Oatman,E.R.,J.A.McMurtry,andV.Voth.1968. Suppressionofthetwo-spottedspidermiteonstrawberrywith massreleasesof Phytoseiuluspersimilus. J.Econ.Entomol. 61:15171521. Port,C.M.,andN.E.A.Scopes.1981. Biologicalcontrolby predatorymites( Phytoseiuluspersimilis Athias-Henriot) ofredspidermite( Tetranychusurticae Koch)infestingAugust2006RHODESANDLIBURD:CONTROLOFTWOSPOTTEDSPIDERMITES1297

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strawberriesgrowninwalk-in'plastictunnels.Plant Pathol.30:9599. Price,J.2002. NewAcramite50WSmiticidenowavailable. UniversityofFlorida.InstituteofFoodandAgricultural SciencesExt.Newsl.Berry/VegetableTimes7:12. Sances,F.V.,N.C.Toscano,E.R.Oatman,L.F.Lapre,M.W. Johnson,andV.Voth.1982. Reductionsinplantprocessesby Tetranychusurticae (Acarina:Tetranychidae) feedingonstrawberry.Environ.Entomol.11:733737. Sances,F.V.,J.A.Wyman,I.P.Ting,R.A.VanSteenwyk, andE.R.Oatman.1981. Spidermiteinfestationswith photosynthesis,transpirationandproductivityofstrawberry.Environ.Entomol.10:442448. SASInstitute.2002. TheSASsystem9.0forWindows.SAS Institute,Cary,NC. Trumble,J.T.,andJ.P.Morse.1993. Economicsofintegratingthepredaceousmite Phytoseiulusperimilis (Acari: Phytoseiidae)withpesticidesinstrawberries.J.Econ. Entomol.86:879885. Waite,G.K.1988. Integratedcontrolof Tetranychusurticae instrawberriesinsouth-eastQueensland.Exp.Appl.Acarol.5:2332. White,J.C.2004. DevelopingIPMstrategiesforcontrolof twospottedspidermitesinstrawberriesinnorth-central Florida.M.S.thesis.UniversityofFlorida,Gainesville,FL. White,J.C.,andO.E.Liburd.2005. Effectsofsoilmoisture andtemperatureonreproductionanddevelopmentof twospottedspidermite(Acari:Tetranychidae)instrawberries.J.Econ.Entomol.98:154158. Received22September2005;accepted2March2006. 1298JOURNALOFECONOMICENTOMOLOGYVol.99,no.4
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