Do Mosquito Misting Systems Do Mosquito Misting Systems Contribute to Resistance?Contribute to Resistance?

Joseph M. ConlonJoseph M. Conlon

Technical AdvisorTechnical Advisor

American Mosquito Control AssociationAmerican Mosquito Control Association

What is Resistance?What is Resistance?

The ability, in a population of insects, to The ability, in a population of insects, to tolerate doses of a pesticide that would be tolerate doses of a pesticide that would be lethal to the majority of the individuals in a lethal to the majority of the individuals in a normal population of the same species, and normal population of the same species, and developed as a result of the selection pressure developed as a result of the selection pressure exerted by the insecticide.exerted by the insecticide.

Resistance MechanismsResistance Mechanisms

Pyrethroids – act by binding with sodium Pyrethroids – act by binding with sodium channel protein, causing nerve to be channel protein, causing nerve to be permanently switched on: “permanently switched on: “kdrkdr”” Persistent activation of sodium channels by Persistent activation of sodium channels by

delaying normal voltage-dependent deactivationdelaying normal voltage-dependent deactivation Increase in permeability due to lesions produced Increase in permeability due to lesions produced

by pyrethroidsby pyrethroids Resistance due to altered sodium channel proteinResistance due to altered sodium channel protein

Resistance MechanismsResistance Mechanisms

EsterasesEsterases Bind and sequesterBind and sequester

Culex resistanceCulex resistance

Amplification/over expression of genes encoding Amplification/over expression of genes encoding xenobiotic metabolizing enzymesxenobiotic metabolizing enzymes

Low fitness cost compared to gene structure alterationLow fitness cost compared to gene structure alteration Anopheline resistanceAnopheline resistance

kdrkdr – reduction in site sensitivity of the voltage-gated – reduction in site sensitivity of the voltage-gated sodium channels to binding of insecticidessodium channels to binding of insecticides

Fitness cost - genes occur at low frequency unless selected forFitness cost - genes occur at low frequency unless selected for

Resistance MechanismsResistance Mechanisms

Monooxygenase – P450 gene binds molecular oxygen Monooxygenase – P450 gene binds molecular oxygen and introduces the oxygen molecule into substrateand introduces the oxygen molecule into substrate Elevated in Anopheles and Elevated in Anopheles and C. quinquefasciatusC. quinquefasciatus Primary mechanism in pyrethrum resistancePrimary mechanism in pyrethrum resistance High fitness cost due to gene alterationHigh fitness cost due to gene alteration

Glutathione S-transferase (GST)Glutathione S-transferase (GST) Binds the insecticide to glutathione, making it more water Binds the insecticide to glutathione, making it more water

solublesoluble More easily excreted More easily excreted

Resistance ManagementResistance Management

Management by Moderation - spare portion of Management by Moderation - spare portion of susceptible genotypessusceptible genotypes Low dose Low dose Non-persistent chemicals – no slow releaseNon-persistent chemicals – no slow release Leave certain generations untreatedLeave certain generations untreated Preserving refugiaPreserving refugia Apply locallyApply locally High thresholds High thresholds

Resistance ManagementResistance Management

Management by Saturation – overwhelm Management by Saturation – overwhelm defense mechanisms by high dosagesdefense mechanisms by high dosages Apply dosages sufficiently high to be lethal to Apply dosages sufficiently high to be lethal to

susceptible as well as heterozygous-resistantsusceptible as well as heterozygous-resistant Prevents buildup of homozygous resistantPrevents buildup of homozygous resistant Use of synergistsUse of synergists

May not work with OPsMay not work with OPs

Resistance ManagementResistance Management

Lower selection pressureLower selection pressure Remove selective advantage – increase fitness Remove selective advantage – increase fitness

costcost IPMIPM

Factors Affecting Resistance Factors Affecting Resistance ManagementManagement

GeneticGenetic Frequency/dominance of resistant alleles - How extensive is resistanceFrequency/dominance of resistant alleles - How extensive is resistance Past selection by other chemicalsPast selection by other chemicals Fitness factors – competitive disadvantage Fitness factors – competitive disadvantage

BioticBiotic Generations/yearGenerations/year Offspring/generationOffspring/generation Single/multiple matingsSingle/multiple matings

Behavior/ecologicalBehavior/ecological Migration, mobility, isolationMigration, mobility, isolation Monophagy/polyphagy – feeding on many hosts reduces exposureMonophagy/polyphagy – feeding on many hosts reduces exposure

ChemicalChemical Mode of actionMode of action Relationship to previously used chemicalsRelationship to previously used chemicals PersistencePersistence

ApplicationApplication Rate, frequency and size of areaRate, frequency and size of area Life stage – treat only one stageLife stage – treat only one stage Application threshold – lower thresholds yield quicker resistanceApplication threshold – lower thresholds yield quicker resistance

Resistance in MosquitoesResistance in Mosquitoes

Harris County Texas – resmethrin (ScourgeHarris County Texas – resmethrin (Scourge©)©) 0.003 lbs AI/acre – no control0.003 lbs AI/acre – no control 0.007 lbs AI/acre – 40% control0.007 lbs AI/acre – 40% control Recovered resmethrin mortality at 0.007 lbs AI/acre within Recovered resmethrin mortality at 0.007 lbs AI/acre within

one year of malathion rotationone year of malathion rotation California California

C. tarsalisC. tarsalis – resmethrin, permethrin and pyrethrum – resmethrin, permethrin and pyrethrum Contra Costa, Fresno, Merced, Riverside, SacramentoContra Costa, Fresno, Merced, Riverside, Sacramento

C. pipiensC. pipiens – pyrethrum, permethrin, deltamethrin and – pyrethrum, permethrin, deltamethrin and lambda-cyhalothrinlambda-cyhalothrin

MarinMarin

Do MMS Contribute To Resistance?Do MMS Contribute To Resistance?

Sublethal dosing – increases selection pressureSublethal dosing – increases selection pressure 90% control in heavily vegetated areas may 90% control in heavily vegetated areas may

require 2x-3x maximum label raterequire 2x-3x maximum label rate Resistance not monitoredResistance not monitored No rotation of insecticidesNo rotation of insecticides May kill natural predators in foliageMay kill natural predators in foliage Saturation in one area promotes resistanceSaturation in one area promotes resistance Lessens incentive for IPM implementationLessens incentive for IPM implementation