Download Do Mosquito Misting Systems Contribute to Resistance?

Do Mosquito Misting Systems
Contribute to Resistance?
Joseph M. Conlon
Technical Advisor
American Mosquito Control Association
What is Resistance?
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The ability, in a population of insects, to
tolerate doses of a pesticide that would be
lethal to the majority of the individuals in a
normal population of the same species, and
developed as a result of the selection pressure
exerted by the insecticide.
Resistance Mechanisms
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Pyrethroids – act by binding with sodium
channel protein, causing nerve to be
permanently switched on: “kdr”
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Persistent activation of sodium channels by
delaying normal voltage-dependent deactivation
Increase in permeability due to lesions produced
by pyrethroids
Resistance due to altered sodium channel protein
Resistance Mechanisms
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Esterases
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Bind and sequester
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Amplification/over expression of genes encoding
xenobiotic metabolizing enzymes
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Culex resistance
Low fitness cost compared to gene structure alteration
Anopheline resistance
kdr – reduction in site sensitivity of the voltage-gated
sodium channels to binding of insecticides
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Fitness cost - genes occur at low frequency unless selected for
Resistance Mechanisms
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Monooxygenase – P450 gene binds molecular oxygen
and introduces the oxygen molecule into substrate
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Elevated in Anopheles and C. quinquefasciatus
Primary mechanism in pyrethrum resistance
High fitness cost due to gene alteration
Glutathione S-transferase (GST)
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Binds the insecticide to glutathione, making it more water
soluble
More easily excreted
Resistance Management
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Management by Moderation - spare portion of
susceptible genotypes
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Low dose
Non-persistent chemicals – no slow release
Leave certain generations untreated
Preserving refugia
Apply locally
High thresholds
Resistance Management
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Management by Saturation – overwhelm
defense mechanisms by high dosages
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Apply dosages sufficiently high to be lethal to
susceptible as well as heterozygous-resistant
Prevents buildup of homozygous resistant
Use of synergists
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May not work with OPs
Resistance Management
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Lower selection pressure
Remove selective advantage – increase fitness
cost
IPM
Factors Affecting Resistance
Management
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Genetic
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Biotic
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Migration, mobility, isolation
Monophagy/polyphagy – feeding on many hosts reduces exposure
Chemical
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Generations/year
Offspring/generation
Single/multiple matings
Behavior/ecological
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Frequency/dominance of resistant alleles - How extensive is resistance
Past selection by other chemicals
Fitness factors – competitive disadvantage
Mode of action
Relationship to previously used chemicals
Persistence
Application
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Rate, frequency and size of area
Life stage – treat only one stage
Application threshold – lower thresholds yield quicker resistance
Resistance in Mosquitoes
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Harris County Texas – resmethrin (Scourge©)
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0.003 lbs AI/acre – no control
0.007 lbs AI/acre – 40% control
Recovered resmethrin mortality at 0.007 lbs AI/acre within
one year of malathion rotation
California
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C. tarsalis – resmethrin, permethrin and pyrethrum
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Contra Costa, Fresno, Merced, Riverside, Sacramento
C. pipiens – pyrethrum, permethrin, deltamethrin and
lambda-cyhalothrin
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Marin
Do MMS Contribute To Resistance?
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Sublethal dosing – increases selection pressure
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90% control in heavily vegetated areas may
require 2x-3x maximum label rate
Resistance not monitored
No rotation of insecticides
May kill natural predators in foliage
Saturation in one area promotes resistance
Lessens incentive for IPM implementation