Establishment and dispersal of the re ant decapitating - PDF document

Establishmentanddispersalofthe“reantdecapitating”yPseudacteontricuspisinNorthFloridaSanfordD.Porter,LuizAlexandreNogueiradeSandLloydW.MorrisonUSDA-ARS,CenterforMedical,AgriculturalandVeterinaryEntomology,P.O.Box14565,Gainesville,FL32604,USAriodeQuarentenaCostaLima,EmbrapaMeioAmbiente,P.O.Box69,13.820-000,Jaguarina,SP,BrazilReceived28February2002;accepted21June2003Thedecapitating”yPseudacteontricuspisBorgmeierwasreleasedateightsitesinNorthFloridabetweenthesummerof1997andthefallof1999asaself-sustainingbiocontrolagentoftheredimported“reant,SolenopsisinvictaBuren.Severalreleasesusedparasitized“reantworkerswhilemostinvolvedadult”iesreleasedoverdisturbedantmounds.Establishmentanddispersalof”ypopulationsweremonitoredbydisturbingabout10“reantmoundsateachsiteandtheninspectingthemcloselyforhovering”iesoveraperiodofabout30min.Overwinteringpopulationsof”iesweresuccessfullyestablishedat6of8releasesites.Overseveralyears,”ypopulationsatthesesitesincreasedtolevelsashighorhigherthanthosenormallyseenintheirSouthAmericanhomeland.Bythefallof1999,”ieshadexpandedout1…6kmfrom“vereleasesitesandoccupiedabout125km.Bythefallof2000the“veinitialreleasesitesplusonenewsitehadfusedintoonelargeareaabout70kmindiameter.The”ieshadexpandedoutanadditional16…29kmandoccupiedabout3300km.Bythefallof2001the”ieshadexpandedoutanadditional10…30kmandoccupiedap-proximately8100km.FlydispersalwasnotrelatedtowindpatternsintheGainesvillearea.Basedontheaboveratesofdispersalandanestablishmentrateof66%,weestimatethatastatethesizeofFloridawouldrequire5…10releasesspacedovera3-yearperiod BiologicalControl29(2004)179…188 www.elsevier.com/locate/ybcon Correspondingauthor.Fax:1-352-374-5818.E-mailaddress:sdp@nersp.nerdc.u”.edu(S.D.Porter).1049-9644/$-seefrontmatter2003ElsevierInc.Allrightsreserved.doi:10.1016/S1049-9644(03)00149-X years,dozensofnaturalenemieshavebeenreportedinSouthAmericacomparedtoonlyafewintheUnitedStates(Jouvenaz,1983;Jouvenazetal.,1977).Interestinthesenaturalenemieswanedbecausenoneofthemseemedlikelytokilllargenumbersof“reantcolonies.However,interestinself-sustainingbiologicalcontrolagentswasrekindledintheearly1990swhenresearchersdiscoveredthat“reantpopulationsintheUnitedStatesare5…7timeshigherthantheyareintheirSouthAmericanhomelands(Porteretal.,1992,1997b).Acarefulevalua-tionofmanypossiblefactorsleftescapefromnaturalenemiesasthemostlikelyexplanationforinterconti-nentalpopulationdi
erences(Porteretal.,1997b).Re-searchersbegantorealizethat“reantbiocontrolismorelikeweedbiocontrolthanbiocontrolofcroppestsinthat“reantenemiesdonotneedtokillacolonydirectlytoreduce“reantpopulations(FeenerandBrown,1992).Enemieslikepathogensandparasitessimplyneedtostress“reantcoloniessucientlysothattheecologicalbalanceisshiftedinfavorofnativeants(Porter,1998a).Ifthishappens,“reantcolonieswouldbeout-competedandpopulationdensitiesofthispestintheUnitedStateswoulddroptolevelsmorelikethosenormallyfoundinSouthAmericawhere“reantsarenotconsideredamajorpest.Formostofthelastdecade,decapitating”iesinthePseudacteonhavebeenthesubjectofintensivere-searche
ortsofscientistsatourUSDA-ARSlaboratoryinGainesville,Florida(Porter,1998a),andbycolleaguesattheUniversityofTexasatAustin(GilbertandPatrock,2002)andcooperatorsinSouthAmerica.PreviousresearchersreportedthatPseudacteon”ieswereattractedSolenopsis“reantsandappearedtoovipositonorinthem(Borgmeier,1921;WilliamsandWhitcomb,1974).SubsequentresearchdiscoveredtheimmaturestagesofPseudacteon”ies(Porteretal.,1995b)andasuiteofspeci“cbehaviorsthat“reantsusetodefendagainstat-tacksofthese”ies(FeenerandBrown,1992;Orretal.,1995;Porteretal.,1995c).Thesedefensescouldonlyhaveevolvedandbeenmaintainedifdecapitating”ieswerehavingpopulationlevelimpactson“reantcoloniesortheirproductionofsexualreproductives.Ofalmost20possiblespecies(PorterandPesquero,2001),weselectedPseudacteontricuspisBorgmeierforreleasebecausestudiesshowedthatthis”ywasveryhost-speci“c(GilbertandMorrison,1997;Porter,1998b;PorterandAlonso,1999;Porteretal.,1995a)andbecauseitwasthe“rstspeciestobesuccessfullyrearedinthelaboratory(Porteretal.,1997a).Thisspecieswasalsoselectedbecauseitwasoneof2…3verycommonspeciesintheregionsaroundthecitiesofJaguariunaandRioClarointhestateofSaoPaulo,Brazil(Porter,1998a)wheretheseniorauthordidmostofhis“eldwork(1994…1997).Pseudacteontricuspiswas“rstreleasedintheUnitedStatesinTexas(Gilbert,1996)beginningin1995.Unfortunately,theseinitialattemptsfailed,probablybecauselownumbersof”ieswereinvolvedandbecauseweatherconditionswerehotanddry.The“rstsuc-cessfulreleaseoccurredinNorthFloridainthelatesummerof1997(Porteretal.,1999).AdditionalreleaseshavealsobeenmadewiththeassistanceofcooperatorsinArkansas(1998),Texas(1998…present),Alabama(1998…2001),SouthCarolina(1999…2001),Louisiana(1999…2001),Mississippi(2000),Oklahoma(1999…2000),Tennessee(1999),NorthCarolina(2000),andGeorgia(2000).Thefateofthesereleaseswillbedis-cussedinsubsequentpapers.Theobjectiveofthispaperistodocumenttherelease,establishment,anddispersalofthedecapitating”y,P.tricuspisaroundGainesville,Florida.Wewillalsousedatafromthisstudytoesti-matethenumberofreleasesneededforthese”iestooccupyastateinaspeci“edperiodoftime.2.Materialsandmethods2.1.FliesreleasedP.tricuspis”iesreleasedinthisstudyoriginatedfrom”iescollectedattheLaboratoriodeQuarentenaCostaLima,EmbrapaMeioAmbiente,JaguariStateofSaoPaulo,BrazilduringlateMayandearlyJune1996.FlieswerecollectedwhileattackingS.invictaandSolenopsissaevissimaF.Smith“reants.These”iesweretheBrazilianformofP.tricuspisasillustratedbyPorterandPesquero(2001,Fig.19a).Theyareverysmall”ies,1.0…1.8mminlengthaboutthesizeofthe“reantheadsfromwhichtheyemerge.Theywereex-portedfromBrazilunderpermitsfromtheMinisterioTecnologico,theInstitutoBrasileirodoMeioAmbienteedosRecursosNaturaisRenovaveis(IBAMA),andtheMinisteriodaAgricultura,PecuariaeAbastecimento(MAPA).TheywereimportedintoquarantinefacilitiesinGainesville,FLunderapermitfromUSDA-APHISwithnoti“cationoftheUSFWS.Weappliedfor“eldreleaseafterconductinganextensiveevaluationofhostspeci“city(GilbertandMorrison,1997;Porter,1998b;PorterandAlonso,1999;Porteretal.,1995a),writinganenvironmentalassessment,andobtainingaUSDA-ARSFindingofNoSigni“cantImpact(FONSI)onnontargetorganisms.The”ieswerereleasedunderapermitfromtheFloridaDepartmentofAgricultureandwiththeacquiescenceofUSDA-APHIS.Voucherspecimensofthe”iesweredepositedintheFloridaStateCollectionofArthropods(FSCA),Gainesville,FL.2.2.ReleasemethodsDependingonthereleasesite(Table1),”ieswereeitherintroducedintothe“eldasadult”iesorasim-maturesinparasitized“reantworkers.Releasemethodsvariedovertime.S.D.Porteretal./BiologicalControl29(2004)179…188 Initially,wesimplyreleasedadult”iesneardisturbed“reantmounds.Eventually,wedevelopedaprotocolwhere25…40adult”ieswereallowedto”youtofawide-mouthedcontainertoanewlydisturbed“reantmound20…30cmaway.Inordertokeepantsactiveonthesurfaceandavailablefor”yattacks,“reantmoundsweredisturbedevery3…10minforupto2h.Progressivee
ortsatcolonydisturbanceusuallyresultedinlevelingtheearthenmoundsthat“reantsbuildandweoftendug10…15cmbelowthesurface.Whenweatherconditionswerehotanddry,shadingthemoundswithseveralstyrofoamplatesonwire”agshelpedkeeptheantsac-tiveasdidsprinklingseverallitersofwateroverthemoundanhourorsobeforetherelease.Wealsofoundthatmaceratingseveralpinchesofantsbetweenour“ngersjustpriortoreleasingthe”ieshelpedstimulateattacks(VanderMeerandPorter,2001).Atseveralsites,wereleasedimmature”iesinpara-sitizedworkers.Thiswasdonebyshovelingdirtwith5…15gofantsandbroodfromamoundintoabucket.Theseworkerswerethenseparatedfromthesoilinthelaboratorybydrip”otation(Banksetal.,1981).Workerswereseparatedfrombroodusingsortingsheetsandsieved(PorterandTschinkel,1985)toremoveex-cesslargeandsmallworkersnotnormallyparasitizedbyP.tricuspis(Morrisonetal.,1999b).Weusedworkersthatpassedthrougha#16sieve(USStandard),butwereretainedbya#20sieve.Groupsof0.8gofsievedants(400…500individuals)fromasinglecolonytogetherwith1gofbroodwereplacedinattacktraysinthelabwhere”ieswereallowedtoparasitizetheantsfor2days.Theseantswerereturnedtotheirmothercolonies3…4daysaftertheywerecollected.2.3.ReleasesitesLocationsofreleasesitesareindicatedinFig.3.Datesandmethodsofreleasing”iesaresummarizedinTable1.The“rst“eldreleaseofP.tricuspisinFloridawasconductedatKanapahaBotanicalGardens(Fig.3,siteA)inJuly1997(Table1).Approximately50par-ticipantsatamediaeventwereeachallowedtorelease4…5”iesintheairorneara“reantmound.Onsub-sequentdays,wereleasedabout450additional”iesneardisturbedmounds.Antsfromseveralcolonieswerealsobroughtintothelabwhereovipositing”ieswereal-lowedtoattackthemforseveraldaysbeforetheywerereturnedtotheirmothercolony.Alltold,about700”ieswerereleasedatthissiteinJulyandanother200inmidSeptember.ThesecondseriesofreleaseswasconductedattheHagueDairyFarm(B).Halfofthemoundsusedweremonogynecoloniesaroundtheedgeofasmallpondandtheotherhalfwerepolygynecoloniesabout200mawayalongapastureedge.Severalhundred”ieswerealsoreleasedover“eldcolonies.Thethirdsitewasinapowerlineright-of-waynexttoHogtownCreek(C).Thissitewasalowwettriangleofabout0.3haborderedbytreesontwosidesandbyaroadem-bankmentonthethird.Wereleasedabout800adult”iesatthissiteovermoundsandanother1000”ieswereusedtoparasitizeworkersbroughtintothelab.ThefourthreleaseareawasaroundourUSDAlaboratoryontheUniversityofFloridacampus(D).Thiswasaninformalreleasesite.Afewadult”ieswerereleasedoverdisturbedmounds,butmost�(5000)weresimplyre-leasedoutthebackdoorofthelabwhenwehadtoomany”iestouseinourrearingoperations(July1997…October1999).The“fthreleasesitewasontheMorrillFarm(E)nearLaCrosse.Thissitewasa16-hacowpasture.Thepasturecontainedamixtureoftrees,bu-shes,andseveralponds.Releasesatthissitewerecon-ductedinthespringof1998andthenagaininthelatesummer.ThesixthsitewasjustnorthoftheGainesvilleRegionalAirport(F).Itwasanarrowsitealonga200-mstripofabandonedpavedroad.Eithersideoftheroadwascloselyborderedbyaswampyforest.TheseventhsitewasontheNor”eetFarm(G)nearNew-berry.Thissitewasinanoldabandonedphosphatepit,partofwhichwasusedtograzecattleandtheotherparthadamixtureoftreesandbushes.The“nalsitewasatSandersFarm(H).Thissiteconsistedofa4-hapastureborderedbytreesandseveralhouses. Table1Summaryof“eldreleasesofthe“reantdecapitating”yP.tricuspisaroundGainesville,FL(1997…1999)Site(#Releases)ReleaseperiodFliesusedMoundsusedMethodResultKanapaha(5)9…29Julyand16September199790014(poly)Adult”iesandparasitizedantsFailedDairyFarm(5)1…15September1997120019(both)Both,asaboveFailedHogtownCr.(8)10September…20October1997180024(mono)Both,asaboveSuccessfulCMAVE(many)July1997…October1999�6000Afew(poly)Adult”iesSuccessful?MorrillFarm(11)29April…3June1998160045(mono)ParasitizedantsFailed?MorrillFarm(11)28August…18September1998150025(mono)Adult”iesSuccessfulAirport(9)22September…8October1998180017(mono)Adult”iesSuccessfulNor”eetFarm(5)26October…7December1998110016(mono)Adult”iesSuccessfulSandersFarm(10)25October…9November1999280046(mono)Adult”iesSuccessfulSocialformof“reantcoloniespresent:single-queen(monogyne)ormultiple-queen(polygyne).S.D.Porteretal./BiologicalControl29(2004)179…188 2.4.Monitoring”yestablishmentanddispersalThepresenceofPseudacteon”iesinthe“eldwasdeterminedbypunchingdepressions(15…20cmdiam-eter)in“reantmoundswithahandorasmallshovel.Fliesweredetectedbycloselyinspectingareasarounddisturbedantsforhovering”ies(Fig.1).FlieswereeasilyaspiratedwithanAllen-typedoublechamberas-piratorandcheckedwithahandlensiftherewasanydoubtabouttheiridentity.Asinglepersonusuallymonitored8…10mounds,visitingeachmoundevery5…10minoveraperiodofupto30min.Aftereachob-servation,theantswerestirreduptokeepthemactive.Severalpinchesofantsineachmoundwereusuallymaceratedbetweenthe“ngerstoreleasepheromonesthatattractthe”ies.Monitoringfor”ieswasgenerallydonebetween11:30amand4:30pmondayswithairtemperaturesgreaterthan20Cwhenadult”iesareactive(unpublisheddataandMorrisonetal.,1999a).Sunshades(Fig.1)wereplacedovermoundsonhotsunnydayssothattheantscouldremainactiveonthesurfaceduringthemonitoringperiod.Pseudacteontricuspis”iesprefermediumtomedium-large“reants(Morrisonetal.,1999b),butpolygyneormultiple-queen“reantcolonieshavesubstantiallyfewerlargeworkersthanmonogynecolonies(Greenbergetal.,1985).Inordertodetermineif”ieswerelessabundantinareaswithpolygyne“reants,wescoredobservationsitesaspolygyne(P),mostlypolygyne(P/M),monogyne(M),ormostlymonogyne(M/P)basedprimarilyonthesizeandcolorofworkersin“reantmoundsinspectedfor”ies.3.ResultsEvenaftermorethan60yearswithoutPseudacteonparasitoids,theimported“reantsaroundGainesvillestillrecognizedthese”iesasenemies.Coloniesunderattackbyseveral”iesoftenshowedgreatlyreducedac-tivity.Thisbehaviorwasoftenthe“rstcluethat”ieswerepresent.Workersincoloniesunderheavyattackalsofrozemotionlessintightclustersjustlike“reantsinSouthAmericado.3.1.FateofreleasesResultsofour”yreleasesaresummarizedinTable1.The“rstreleaseatKanapahaGardenswasapparentlynotsuccessfulasno“eld-reared”ieswererecoveredduringrepeatedobservationsoverthenext9months.WeweremoresuccessfulwiththesecondreleaseattheDairyFarmwherewefoundsome“eld-reared”ies,about24total,50…60daysafterthe“rstrelease,butnonethereafter.Field-reared”ieswerecollectedfromtheHogtownCreeksite44daysaftertheinitialrelease(Table1).Flieswererecoveredeverymonthfromthissiteforthenextyear(Fig.2).Duringa3-monthdroughtinthespringof1998,”ynumberswereverylow,butnumbersincreasedbeginninglateMayandJunewhenthesummerrainsbegan.Thereafter,”ynumbersgraduallyincreaseduntilthefallof2001whentheyjumpedfromseveraldozenper10moundstooverahundred.WedidnotmonitorforestablishmentaroundtheCMAVElaboratoryuntilthemiddleofMayandearlyJune1999.Atthattimeafew”ieswerefoundatseverallocationsaroundthelaboratory.Noadditional”ieswerefoundonthreesampledatesfromJulythrough Fig.1.LloydDavissearchingforPseudacteon”ieshoveringovera“reantmound.Notethatpartofthemoundisshadedbyastyrofoamplateonawire”agandthat”iesarebeingcollectedwithadouble-chamberAllen-typeaspirator. Fig.2.FlyabundanceattheHogtownCreekandMorrillFarmreleasesitesplottedagainsttime.PointsplottedfromOctober1997toOctober1999aremonthlyaveragesof1…4sampledates.Morerecentpointswerenotaveraged.S.D.Porteretal./BiologicalControl29(2004)179…188 September.However,inthemiddleofNovember,webegan“nding”iesatCMAVEandsurroundingsites.Thepatternofdistributionatthattimeindicatedthatreleasesfromourlaboratorywerelikelysuccessful;however,westillcouldnotexcludethepossibilitythatthese”iescamefromtheHogtownCreeksite5…8kmtothewest.The“rstreleasesatMorrillFarmappearedtofailor,atbest,doverypoorly(Table1).Werecoveredonlythree”iesneartheendofJune1998andonethemiddleofJuly,butno”ieswerefoundinAugust.Theapparentfailureofthise
ortcausedustoswitchbackfromre-leasingparasitizedantstoreleasingadult”iesoverdis-turbedmounds.However,itisjustaslikelythatseveredroughtconditionsfromAprilthroughtheendofJuneandfrequentmaximumtemperaturesinexcessof35wereresponsibleforthedearthof”ies.Thesecondre-leasee
ortatMorrillFarmwasmuchmoresuccessful.Asingle”ywasrecoveredinthemiddleofOctober1998andthereafter”ieswerefoundalmosteverysampleperiodforthenextyear(Fig.2).AswithHogtownCreek,”ynumbersgraduallyincreaseduntilthefallof2001whennumbersjumpedfromseveraldozen”iespersampletooverahundred.TheAirportreleasesitewasalsosuccessful.A“eld-reared”ywasfoundon1November1998,40daysafterthe“rst”ieswerereleased.Flieswererecoveredfromthissiteeverymonthforthenextyear,afterwhichregularmonitoringwasdiscontinued.FliesfromtheNor”eetFarmreleasewererecoveredonsixoccasionsfromFebruarytoOctober1999.No”ieswerefoundoneightoccasionsduringthesameperiodincludinga3-monthdearthfromlateApriltolateJuly.However,14”ieswerefoundon6of10moundsinOctober1999,ayearaftertheywerereleased.Largenumbersof”ieswerefoundatSandersFarminearlyJanuaryandagaininlateFebruary2000indicatingthatthereleasewaslikelysuccessful.However,bylatespring2000,theadvancingwavefrontsof”iesfromHogtownCreekandMorrillFarmhadprobablyreachedthissite.Afterthe“rstorsecondyear,”ypopulationsatthesixreleasesites(Fig.2)wereashighorhigherthanthosenormallyseenbytheauthorsinBrazilorArgentina.3.2.DispersalWecheckedfordispersalof”iesoutoftheHogtownCreeksiteinMay1998(foursites)andOctober1998(onesite)andfoundno”iesalongroads0.1…1.4kmawayeventhough”ieswereactiveandcommonatthereleasesite.InJune1999,wefoundseveral”iesatasiteabout5kmsouthwestoftheHogtownCreeksite,butagainno”ieswherefoundatmoundsafewhundredyardsawayfromthesiteatHogtownCreek.FlieswerealsofoundatMorrillFarminJune1999.Wefoundthemat11of13sitesupto0.5kmaway,butnotatfoursitesbeyondthis.InNovemberandDecember1999,wefound”ieshadexpandedout3…4kmfromourreleasesiteatMorrillFarm,1…2kmoutfromourreleasesiteattheairport,and1kmoutfromthereleasesiteatNor”eetFarm Fig.3.Dispersalofthedecapitating”yP.tricuspis(1999…2001)fromreleasesitesinAlachuaCounty,FL.(A)KanapahaGardens,(B)DairyFarm,(C)HogtownCreek,(D)CMAVE,(E)MorrillFarm,(F)Airport,(G)Nor”eetFarm,and(H)SandersFarm.S.D.Porteretal./BiologicalControl29(2004)179…188 (Fig.3).Wefound”ies6,3.5,and2kmtothesouth,west,andnorthoftheHogtownCreekreleasesite,re-spectively.Wefound”ies4,4.2,and3.5kmtothenorth,eastandsouthofourlaboratory.FlieswerealsofoundatfoursitesbetweentheHogtownCreeksiteandourlaboratory.Thispattern(Fig.3)suggeststhat”iesfrombothsites(3.5kmapart)hadfusedtoformalargeel-lipse;however,asmentionedpreviously,itispossiblethatthe”iescamefromtheHogtownCreeksite.Withintheareasenclosingpositivesites,86%ofsites(32/37)contained”ies;outsidetheseareaswehad31negativesites.Takentogetherthe”iesoccupiedabout125kmBythefallof2000,”ieshadexpandedoutanaverageofanadditional19km(range16…29)(Fig.3)andthefourdistributionsfromthepreviousyearhadallfused.FliesappearedtoexpandoutofallbutperhapstheNor”eetsite.DispersaloutoftheNor”eetsiteisuncertainbecausenowestwardmovementwasdetectedandmovementinotherdirectionswouldhavebeenconfoundedwithdis-persaloutoftheothersites.Withintheareaenclosingpositivesites,80%ofsites(63/79)contained”ies;outsidethisareawefound32negativesites.The”ieshadex-pandedtooccupy3300kmbythefallof2000.Thenumberof”iesfoundatsamplesitesdecreasedasthedistancefromreleasesitesincreased(Fig.4).Therateofoutwarddispersalincreasedagainduring2001;the”iesexpandedoutwardanaverageofanad-ditional23km(range10…30)sothattheyoccupiedover8100km.Thedispersalratetothesouthwaslessthanthattothenorth,eastandwest.Withintheareaen-closingpositivesites,86%ofsites(36/42)contained”ies;whileoutsidetheseareaswehad25negativesites.TheaverageairtemperatureduringoursampleswasSD)andtheaveragerelativehumiditywas13%.Theaveragetimeuntilwefoundthe“rst”ywas138min.Abouthalfofoursamplesiteswith”iesappearedtohavepolygyne(P)ormostlypolygyne(P/M)“reantsandhalfhadmonogyne(M)ormostlymonogyne(M/P)“reants,buttherewasnosigni“cantdi
erenceinthenumberof”iesobservedamongthesesites(ANOVA,397).Wefoundthenative“reantSolenopsisgeminata(Fabricius)atsixsiteswherewefoundP.tricuspisattackingimported“reants,but,aspredicted(PorterandAlonso,1999),noneoftheintro-duced”ieswereseenattackingthenative“reants.4.Discussion4.1.EstablishmentThispaperdocumentsthe“rstsuccessfulreleaseandestablishmentofaclassicalbiologicalcontrolagentagainstapestant.Infact,itisthe“rstclassicalbio-controlagentreleasedagainstanysocialinsectpestthathasestablishedandthenexpandedrapidlyacrossthelandscape.ResearchersinNewZealandwereabletosuccessfullyintroduceanichneumonidparasitoidagainstintroducedVespulawasps,butafterabout15yearsthisbiocontrolagentisstillrestrictedtoseveralisolatedreleasesiteswhereitisexpandingslowly(Bar-lowetal.,1998).Unfortunately,therehasneverbeenacasewhereasocialinsectpesthasbeensuccessfullycontrolledwithaself-sustainingbiocontrolagent.Thislackofsuccessispartlyduetolackofe
ort.WiththeexceptionofwaspsinNewZealandand“reantsintheUnitedStates,veryfewattemptshavebeenmadetomanagesocialinsectpestswithclassicalorself-sustain-ingbiologicalcontrolagents(Orretal.,2001).Thislackofe
ortisprobablyduetoignoranceaboutnaturalenemiesofsocialinsectpests,thecomplexityofsocialinsectbiology,andlimitedfundingforresearchthatisnotlikelytoproduceeconomicpro“ts.Nevertheless,thepotentialvalueofusingclassicalbiocontrolagentsagainstsocialinsectsisclearlydemonstratedbytheimpactsoftrachealmitesandseveralkindsofdiseasesonhoneybeepopulations(MorseandNowogrodzki,4.2.DispersalDispersaloutofourreleasesitesacceleratedovertime(Fig.3)sothatbythethirdyear”ieswereex-pandingoutatarateofabout23km/year.Assuming6…8generationsof”iesperyear(SDPunpublisheddata),thismeansthatthebestdispersersineachgenerationof”iesaretraveling3…4km.Most”iesprobablydonotdispersemorethanseveralhundredmeters(Morrisonetal.,1999a)intheirshort1…3daylifespans(Porter,1998a),butatleastafewfemale”iesareevidentlyabletotravelmuchfurther.Theincreasingratesofdispersalmaybeduetoraredispersaleventsbecomingmore Fig.4.Flyabundanceasafunctionofdistancefromnearestreleasesite,fall2000.Alinearregressionisplottedbecausepolynomialregressionswerenotsig-ni“cantlybetter�(0.05).S.D.Porteretal./BiologicalControl29(2004)179…188 commonwithincreasingnumbersof”iesoritispossiblethatrapidlydispersing”iesarebeingselectedforbecausetheyareablecolonizenewhabitatmorefrequently.Thefactthat80…85%ofsamplesiteswithinthewavefrontwerepositivedemonstratedthattheexpandingwavefrontof”iesoccupiedahighpercentageofavail-ablesites.Italsosuggeststhatwewereusuallysuccessfulin“nding”ieswhentheywerepresent;inotherwords,thefrequencyoffalsenegativeswasprobablyrelativelyDecapitating”ieswereascommonatpolygynesitesasatmonogynesites.Perhapsthehigherdensitiesof“reantworkersnormallyfoundinpolygyneareas(2…3times,MacomandPorter,1996;Porter,1992)counter-balancedthelowerfrequenciesoflargerworkers(Greenbergetal.,1985)thatthis”yneedstoproducefemales(Morrisonetal.,1999b).However,itispossiblethatmoreaccurateassessmentsofaverageworkersizesatobservationsitesandactualcensusesofestablished”ypopulationsoverlongerperiodsoftimewouldresultinanegativecorrelationbetweenthesevariables.TherelativelyuniformdispersalpatternsofP.tricu-(Fig.3)donotcorrelatewellwiththestronglybi-directionalwindpatternintheGainesvilleareaduringhoursof”yactivity(Fig.5).Basically,the”iesdonotappearprimarilytodisperseeitherbydriftingwiththewindorby”yingupwindtracking“reantscents.Per-hapsthisisbecausethey”yclosetothegroundwherethewindisgreatlyreduced.Morrisonetal.(2000)foundnocorrelationbetweenwindandtheactivityofnativePseudacteon”iesinTexasalthough”iesdidarriveafewminutessoonerwhenwindswereabove1.9m/satoneoftwosites.Slowdispersaltothesouthin2001maybeduetothehighprevalenceofpolygyne“reantcoloniesinthisregion(Porter,1992);however,asmentionedabove,wedidnotdetectlowerpopulationsof”iesatsiteswithpolygyne“reants.Slowdispersaltothesouthcouldalsobeaquirkofthehabitatorthesamplinge
ortbecausethise
ectwasnotseentheyearbefore.IntheonlyotherstudyofdispersalinPseudacteonMorrisonetal.(1999a)foundthatnativePseudacteonspeciesinTexasdispersedupto650mawayfromtheirnearesthostS.geminatacolony.LittleisknownofdispersalinotherfamiliesofPhoridae(Disney,1994)otherthanthattheyareoftencomponentsoftheaerialplanktoncaughtinnetsoronshipsthousandsofkilo-metersfromland(BowdenandJohnson,1976;Yo-shimotoetal.,1962).ThePhoridaeareaverydiversefamily,however,andtheyarelikelytobecharacterizedbymuchvariationindispersalstrategiesandability.ThedispersalabilityofestablishedP.tricuspis(23km/year)isinthehighrangeofratesreportedforsmallparasitoids.Goldsonetal.(1999)citeddispersalratesof1…2km/yearforseveralhymenopteranparasi-toids,6km/yearforanother,andtensofkilometersperyearforyetanother.Munro(1998)reported13…24km/yearforanichneumonidwaspparasitoidand8…15km/yearforatachinid”yparasitoid.Franketal.(1996)reportedadispersalrateof64km/yearforalargetachinidparasitoidofmolecrickets.Incontrasttotheratesabove,dispersalratesofsomebiocontrolagentsreleasedagainstexoticplantscanbeonlyafewhundredmetersperyearorless(Centeretal.,2000;McClayandDeClerck-Floate,1999)ascanatleastoneparasitoid(Goldsonetal.,1999).4.3.PredictingdispersalratesDeterminingdispersalratesfromreleasesofP.tric-isimportantbecauseitallowsustopredicthowmanyreleaseswouldbenecessarytocoveragivenre-gioninaspeci“edamountoftime.Italsoallowsustochoosereleasesitesthatarespacedatsucientintervalsto“llaregionwithasfewreleasesaspossible.Asde-scribed,dispersalratesvariedamongsites.Duringthe“rstyear,theHogtownsiteshowednoindicationofdispersalevenafewdozenmetersawayfromthereleasesite.Similarly,”iesattheNor”eetsitewereonlyfound1kmfromthereleasearea.Incontrast,”ieswerefound2kmoutafterayearattheAirportsiteand4kmoutafteronlyaboutayearattheMorrillFarmsite.Takentogetherwefeelthat1.5kmwouldbeaconservativeestimatefordispersalattheendofthe“rstyear.Inthe Fig.5.MeanannualwinddriftpatternatGainesvilleRegionalAirport(1999…2001)duringhoursof”yactivity(800…1800h,airtemperatureC;datawerecalculatedbymultiplyingmeanwindspeedforeachof36compassdirectionsbythetotalnumberofhoursthatwindblewtowardeachdirection).WeusedhourlydataretrievedfromNOAANationalClimaticDataCenter(EditedLocalClimatologicalDatatext“le:http://lwf.ncdc.noaa.gov;searchforGainesville,FL).S.D.Porteretal./BiologicalControl29(2004)179…188 secondyear,theNor”eetsitedidnotexpand,buttheHogtownsiteexpandedoutanadditional16km.TheMorrillFarmandAirportsitesexpandedoutanadditional26and23km,respectively.Consequently,wefeelthat15kmwouldbeaslightlyconservativeestimatefortheaddedexpansioninthesecondyear.Bythethirdyear,allthesiteshadfused.Aconservativeestimatefortheaverageexpansionrateinthethirdyearwouldbe20km.Assumingdispersalratesinfutureyearsaresimilartothethirdyear,wecanpredicthowmanysuccessfulre-leasesitwilltaketo“llthestateofFloridainagivenperiodoftime(Fig.6).Onesuccessfulreleaseperyearfor3years(3total)wouldcoverthestateinjustunder9years.Twosuccessfulreleasesperyearfor3years(6total)wouldcoverFloridainabout7years.Finally,foursuccessfulreleasesperyearforeachofthreeyears(12total)would“llFloridainjustover5years.Inotherwords,doublingthereleasee
ortfrom2to4peryearonlyshortenedthecoveragetimeby1.5years(22%).Theseestimates,ofcourse,donottakeintoaccountthegeographicshapeofFlorida.Afewextrareleasesoranotheryearortwowouldprobablybeneededtodis-tributethe”iesthroughoutthepanhandleandoutacrosstheKeys.Ontheotherhand,thethirdyearofreleasescouldprobablybedroppedwiththe4/yearscenariobecausetheywouldaccountforlessthan12%oftheareacoveredafter5years.Additionalreleaseswouldalsoneedtobemadetoreplacethosethatfailed.Wehada66%successrate(Table1),althoughitappearedtoimprovewithlaterreleases.Allthingsconsidered,astatethesizeofFloridacouldprobablybecoveredwith”iesin6…9yearswith5…10releases.Consideringallsoutheasternstatestogetherandaddinginacushionforfailedreleases,weestimatethat90…140releaseswouldbenecessarytocompletethetaskin6…9years(providedcoolertemperaturesinmorenorthernregionsdonotresultinslowerdispersalrates).AdditionalreleasesmayalsobeneededfortheCarib-beanandperhapsCaliforniaandBrisbane,Australiaiferadicationattemptsinthesetwoareasarenotsuc-cessful.Weassumethatsimilarreleasee
ortswouldalsobenecessaryforeachadditionalspeciesorbiotypeof”yimported.4.4.Futureimpactson“reantpopulationsPseudacteondecapitating”iesclearlyimpact“reantpopulationsbecausethatistheonlyway“reantscouldhaveevolvedandcontinuetomaintainspeci“cdefensivebehaviorsagainstthisgroupof”ies(Porter,1998a).Whilethemagnitudeofthisimpactisstillunknown,theimpactofasinglespeciesofdecapitating”yislikelytobesmallormoderate.Severaladditionalspeciesof”iesandothernaturalenemieswillalmostcertainlybenec-essarytoobtainmaximumimpacts(Porter,2000).Itisclearfromourdatathat”ypopulationsrequireseveralyearstoreachmaximumlevels(Figs.2and4).Addi-tionally,ifthe”iesarecapableoftiltingtheecologicalbalanceinfavorofthenativeants,thennativeantsarelikelytoneedanotheryearortwofortheirpopulationstobuildupincompetitionwiththeimported“reants.Inordertoquantifytheimpactsofthis”y,wehavesetupapproximately80monitoringplotsatincreasingdis-tancesfromthereleasesites.Fireantpopulationsattheseplotsarebeingestimatedtwiceayearbymoundcounts,baitsandpitfalltraps.Fliesmovedintothe“rstsetofplotsbetweenspringandfall2000.Overthenextseveralyears,wewillmonitortheimpactofP.tricuspison“reantpopulationsintheseplots.Theultimatere-sultsofourreleasee
ortarestillunknown,butitseemsclearthatself-sustainingbiocontrolagentslikeP.tric-aretheonlyhopewehaveforpermanentcontrolofimported“reantsintherurallandscape.AcknowledgmentsWethankTerezinhadellaLuciaforobtainingtheinitialBrazilianpermitswhichallowedustoexportthe“rstshipmentsof”iesbacktotheUnitedStates.WealsothankHaroldFowlerandOdairBuenofortheirassistanceandsupportwhiletheseniorauthorstudiedthelifehistoryofthese”iesatUNESP,RioClaro,StateofSaoPaulo,Brazil.Similarly,wethankGilbertoJosdeMoraeswhokindlyallowedtheseniorauthorandhisfamilytostayathismountainfarmhomeduringthe“rstmonthwhenseniorauthorworkedatthe Fig.6.Projectionsofdispersalscenariosfrommultiplereleasesof”ies.Thegraphassumes1,2,or4successfulreleasesforeachof3yearsanddispersalratesof1.5kmthe“rstyear,15kmthesecondyear,and20kmeachyearthereafter.TheheavydashedlineindicatesthetotallandareaofFlorida.Forcomparison,theapproximateareas)occupiedby“reantsinothersoutheasternstatesareasfollows:400,000,Oklahoma25,000,Arkansas60,000,Louisiana110,000,Mississippi120,000,Alabama130,000,Tennessee150,000,SouthCarolina110,000,andNorthCarolinaS.D.Porteretal./BiologicalControl29(2004)179…188 LaboratoriodeQuarentenaCostaLima,EmbrapaMeioAmbiente,Jaguariuna,StateofSaoPaulo,Brazil.GaryBuckinghamandRobertoPereiraarethankedforreviewingthemanuscript.LloydDavisisthankedforthemanyhoursthathespentinthe“eldreleasingthe”iesandmonitoringtheirestablishmentanddispersal.ReferencesAllen,G.E.,Silveira-Guido,A.,1974.OccurrenceofmicrosporidiainSolenopsisrichterisp.inUruguayandArgentina.FloridaEntomol.57,327…329.Anon.,1965.Antsversusants.USDA,ARS,Agric.Res.13(11),8…9.Anon.,2001.Thestatewideeconomicimpactoftheredimported“reantinTexas.TexasImportedFireAntResearchandManagementPlan,TexasA&MUniversity9.Banks,W.A.,Lofgren,C.S.,Jouvenaz,D.P.,Stringer,C.E.,Bishop,P.M.,Williams,D.F.,Wojcik,D.P.,Glancey,B.M.,1981.Tech-niquesforcollecting,rearing,andhandlingimported“reants.USDA,SEA,AATS-S-21,9.Barlow,N.D.,Beggs,J.R.,Moller,H.,1998.SpreadofthewaspSphecophagavesparumvesparumfollowingitsreleaseinNewZealand.NewZealandJ.Ecol.22,205…208.Borgmeier,T.,1921.ZurlebensweisevonPseudacteonborgmeieriSchmitz(inlitt.)(Diptera:Phoridae).Z.Deut.Ver.Wiss.KunstSaoPaulo2,239…248.Bowden,J.,Johnson,C.G.,1976.Migratingandotherterrestrialinsectsatsea.In:Cheng,L.(Ed.),MarineInsects.North-Holland,Amsterdam,pp.97…117.Callcott,A.-M.A.,Collins,H.L.,1996.Invasionandrangeexpansionofredimported“reant(Hymenoptera:Formicidae)inNorthAmericafrom1918to1995.FloridaEntomol.79,240…251.Center,T.D.,Van,T.K.,Rayachhetry,M.,Buckingham,G.R.,Dray,F.A.,Wineriter,S.A.,Purcell,M.F.,Pratt,P.D.,2000.FieldcolonizationoftheMelaleucasnoutbeetle(Oxyopsvitiosa)inSouthFlorida.Biol.Control19,112…123.Collins,H.L.,Callcott,A.M.,Lockley,T.C.,Ladner,A.,1992.Seasonaltrendsine
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