PesticidePesticide ResistanceResistance ManagementManagement AnAn InsectInsect PerspectivePerspective
FrankFrank Zalom,Zalom, Dept.Dept. ofof Entomology,Entomology, UCUC DavisDavis NickNick Toscano,Toscano, DeptDept ofof Entomology,Entomology, UCUC RiversideRiverside FrankFrank Byrne,Byrne, DeptDept ofof Entomology,Entomology, UCUC RiversideRiverside
InsecticideInsecticide resistanceresistance isis duedue toto aa geneticgenetic traittrait aa pestpest inheritsinherits thatthat allowsallows itit toto survivesurvive anan applicationapplication thatthat mostmost otherother individualsindividuals inin thethe populationpopulation cannotcannot survive.survive.
TheThe survivorsurvivor thenthen passespasses thethe genesgenes forfor resistanceresistance onon toto thethe nextnext generation.generation.
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TheThe moremore thethe insecticideinsecticide isis used,used, thethe moremore quicklyquickly susceptiblesusceptible individualsindividuals areare eliminatedeliminated andand thethe fasterfaster thethe proportionproportion ofof resistantresistant individualsindividuals increasesincreases inin thethe population.population.
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X IncreasingIncreasing pesticidepesticide ratesrates ResistanceResistance MechanismsMechanisms InsecticideInsecticide avoidanceavoidance behaviorsbehaviors -- • InsectsInsects maymay changechange theirtheir behaviorbehavior inin orderorder toto avoidavoid thethe pesticide.pesticide. BiochemicalBiochemical mechanismsmechanisms -- • ResistantResistant insectsinsects possesposses enzymesenzymes thatthat breakbreak downdown thethe pesticidepesticide oror thethe pesticidepesticide maymay notnot affectaffect themthem inin thethe samesame way.way.
FactorsFactors InfluencingInfluencing SelectionSelection BiochemicalBiochemical mechanismsmechanisms • TargetTarget sitesite resistanceresistance -- decreasesdecreases sensitivitysensitivity ofof targettarget sitesite (e.g.(e.g. nerves);nerves); insecticideinsecticide nono longerlonger bindsbinds toto itsits target.target. • DetoxificationDetoxification -- occursoccurs whenwhen enzymesenzymes (e.g.(e.g. esterases,esterases, oxidases,oxidases, oror glutathioneglutathione S-S- transferasestransferases (GST))(GST)) preventprevent thethe insecticideinsecticide fromfrom reachingreaching itsits sitesite ofof action.action. • CuticularCuticular penetrationpenetration -- reducedreduced movementmovement ofof pesticidepesticide throughthrough thethe insect’sinsect’s cuticle.cuticle.
FactorsFactors InfluencingInfluencing SelectionSelection BiochemicalBiochemical mechanismsmechanisms • Cross-resistanceCross-resistance -- PestPest isis resistantresistant toto 22 oror moremore pesticides,pesticides, andand thethe samesame genesgenes mediatemediate thethe resistance.resistance.
OnceOnce aa pestpest exhibitsexhibits resistanceresistance toto oneone pesticide,pesticide, resistanceresistance toto otherother pesticidespesticides withwith thethe samesame modemode ofof actionaction maymay followfollow moremore quickly.quickly.
TargetTarget SiteSite ResistanceResistance MechanismsMechanisms TheThe targettarget ofof organophosphatesorganophosphates (e.g.(e.g. azinphosmethyl,azinphosmethyl, diazinon,diazinon, chlorpyrifos)chlorpyrifos) andand carbamatescarbamates (e.g.,(e.g., carbarylcarbaryl andand methomyl)methomyl) isis acetylcholinesteraseacetylcholinesterase (ache)(ache) inin nervenerve synapses.synapses. AtAt leastleast fivefive pointpoint mutationsmutations inin thethe (ache)(ache) insecticide-bindinginsecticide-binding sitesite havehave beenbeen identifiedidentified thatthat singlysingly oror togethertogether causecause varyingvarying degreesdegrees ofof reducedreduced sensitivitysensitivity toto OPsOPs andand carbamates.carbamates.
TargetTarget SiteSite ResistanceResistance MechanismsMechanisms TheThe targettarget ofof organochlorinesorganochlorines (e.g.(e.g. DDT)DDT) andand syntheticsynthetic pyrethroidspyrethroids areare thethe sodiumsodium channelschannels ofof thethe nervenerve sheath.sheath. TheirTheir commoncommon resistanceresistance mechanismmechanism isis referredreferred toto asas "knockdown"knockdown resistance"resistance" (kdr)(kdr) oror target-sitetarget-site insensitivity.insensitivity.
TargetTarget SiteSite ResistanceResistance MechanismsMechanisms TheThe genesgenes thatthat conveyconvey kdrkdr areare recessive.recessive. RecessiveRecessive genesgenes cancan persistpersist atat lowlow levelslevels inin aa populationpopulation withoutwithout beingbeing detecteddetected eveneven ifif nono selectionselection pressurepressure isis present.present. InIn 1980,1980, atat leastleast 229229 insectinsect pestspests werewere documenteddocumented toto bebe resistantresistant toto DDT.DDT.
DetoxificationDetoxification MechanismsMechanisms TheThe enzymesenzymes responsibleresponsible forfor detoxificationdetoxification areare transcribedtranscribed byby membersmembers ofof largelarge multigenemultigene familiesfamilies ofof esterases,esterases, oxidases,oxidases, andand GST.GST. TheThe mostmost commoncommon resistanceresistance mechanismsmechanisms inin insectsinsects areare modifiedmodified levelslevels oror activitiesactivities ofof esteraseesterase detoxificationdetoxification enzymesenzymes thatthat metabolizemetabolize aa widewide rangerange ofof insecticides.insecticides.
CrossCross resistanceresistance forfor selectedselected insecticideinsecticide classesclasses
carbamatescarbamates AcheAche organophosphatesorganophosphates EsterasesEsterases pyrethroidspyrethroids kdrkdr OxidasesOxidases
DDTDDT IGRsIGRs
FactorsFactors InfluencingInfluencing SelectionSelection Biological/ecologicalBiological/ecological factorsfactors -- • LifeLife spanspan ofof insect/insect/ numbernumber ofof generationsgenerations • ReproductiveReproductive capacitycapacity -- • MobilityMobility -- • AvailabilityAvailability ofof refugiarefugia -- • PolyphagyPolyphagy vs.vs. monophagymonophagy (host(host range)range) --
FactorsFactors InfluencingInfluencing SelectionSelection OperationalOperational factorsfactors -- ThoseThose factorsfactors relatedrelated toto thethe applicationapplication ofof pesticidespesticides including:including: • ChoiceChoice ofof pesticidepesticide • TimingTiming • DoseDose • PersistencePersistence
ResistanceResistance MonitoringMonitoring MonitoringMonitoring detectsdetects tolerancetolerance toto pesticidespesticides inin pestpest populationspopulations beforebefore resistanceresistance becomesbecomes widespread.widespread.
ResistanceResistance MonitoringMonitoring TopicalTopical bioassaysbioassays -- exposeexpose insectsinsects toto aa discriminatingdiscriminating dosedose ofof anan insecticide.insecticide. • DippingDipping -- dipdip intointo pesticidepesticide • CagingCaging -- confineconfine toto sprayedsprayed fruitfruit oror leafleaf • Petri-dishPetri-dish bioassaysbioassays -- onon aa treatedtreated dishdish (or(or vialvial oror plasticplastic baggie)baggie) surfacesurface • PheromonePheromone cardcard bioassaysbioassays -- adultsadults capturedcaptured onon pheromonepheromone trapstraps RangeRange ofof dosesdoses requiredrequired toto determinedetermine discriminatingdiscriminating dosedose == researchresearch ResistanceResistance MonitoringMonitoring ELISAELISA teststests -- developeddeveloped forfor insectsinsects thatthat useuse knownknown enzymesenzymes toto resistresist thethe pesticide.pesticide.
ProportionProportion ofof LygusLygus BugsBugs KilledKilled
Bifenthrin (Brigade) Malathion Bifenthrin (Brigade) 100 ug in Bioassay Bag 200 ug in Bioassay Bag 100 ug in Bioassay Bag
100 100 90 90 80 80 Garey Garey 70 70 Santa Maria Santa Maria 60 Salinas 60 Salinas 50 Prunedale 50 Prunedale 40 Riverside Rd 40 Riverside Rd San Andreas 30 San Andreas 30 UC Davis UC Davis 20 20 10 10 0 0
Methomyl (Lannate) Fenpropathrin (Danitol) 1.5 ug in Bioassay Bag 100 ug in Bioassay Bag 100 100 90 90 80 80 Garey Garey 70 70 Santa Maria Santa Maria 60 60 Salinas Salinas 50 Prunedale 50 Prunedale Riverside Rd 40 Riverside Rd 40 San Andreas 30 San Andreas 30 UC Davis UC Davis 20 20 10 10 0 0 ResistanceResistance ManagementManagement StrategiesStrategies • ChangeChange frequencyfrequency ofof application,application, useuse onlyonly whenwhen necessarynecessary basedbased onon monitoringmonitoring andand economiceconomic thresholdsthresholds • LocalLocal ratherrather thanthan areawideareawide treatmentstreatments • TakeTake intointo considerationconsideration lifelife stagesstages ofof aa pest,pest, treattreat thethe moremore susceptiblesusceptible stagestage • MaintainMaintain untreateduntreated refugesrefuges • UseUse lessless persistentpersistent pesticidespesticides
ResistanceResistance ManagementManagement StrategiesStrategies • UseUse rotationsrotations ofof insecticidesinsecticides withwith differentdifferent modesmodes ofof actionaction • UseUse recommendedrecommended highhigh ratesrates • UseUse selectiveselective pesticidespesticides • PesticidePesticide mixturesmixtures inin suitablesuitable areasareas • PromotePromote useuse ofof naturalnatural enemiesenemies withwith pesticidepesticide tolerancetolerance TheThe goalgoal ofof resistanceresistance managementmanagement isis toto conserveconserve geneticgenetic susceptibilitysusceptibility ofof aa population.population.
PesticidePesticide ResistanceResistance IsIs NotNot TheThe OnlyOnly FactorFactor InfluencingInfluencing EfficacyEfficacy (It(It maymay notnot eveneven bebe thethe mostmost importantimportant factor)factor) • InadequateInadequate coveragecoverage • IncorrectIncorrect pesticidepesticide raterate oror calibrationcalibration • ImproperImproper treatmenttreatment timingtiming • IncompatibilityIncompatibility withwith otherother pesticidespesticides oror adjuvantsadjuvants • pHpH • TemperatureTemperature • ImmigrationImmigration afterafter treatmenttreatment appliedapplied
PesticidePesticide ResistanceResistance ManagementManagement AnAn InsectInsect PerspectivePerspective
FrankFrank Zalom,Zalom, Dept.Dept. ofof Entomology,Entomology, UCUC DavisDavis NickNick Toscano,Toscano, DeptDept ofof Entomology,Entomology, UCUC RiversideRiverside FrankFrank Byrne,Byrne, DeptDept ofof Entomology,Entomology, UCUC RiversideRiverside