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Techniques for Evaluating Insecticide Resistance in Filth Flies R esistance Profiles: Which Test To Use? Phil Kaufman Entomology and Nematology Dept. University of Florida
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Background Resistance is genetic, therefore inherited –Return to susceptibility not guaranteed Speed of return is quite variable Resistance is a population phenomenon –All sampling methods are biased –All testing methods are biased –We must identify our needs…. and choose according to our abilities
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Susceptible Individuals Predominate Insecticide Application
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Resistant Individuals Predominate Susceptibles still present, few in number
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How to evaluate? Biochemical/Immunological (Genotypic) methods –Molecular tools targeting physiological processes –Genetic mapping - Sequencing/gene expression Phenotypic methods –Exposure followed by death counts
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Treat and Count Technical or Formulated? –Technical much more precise Very precise results Eliminate effect of formulation shifts Eliminate concentration problems of formulations –Formulated often much easier Loss of precision - more variables Can compare different formulations Provides a “real world” result
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Insect issues….. Lab reared or Field collected? –Lab provides a more even comparison No parasites, healthy Similar sized/aged organisms Genetic bottleneck? –Field No rearing issues Faster turnaround Variable size/age/health
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Insect issues….cont. What stage to use? –Often the stage that is pestiferous - Adult Insect sex –Important differences between sexes Size, metabolism, longevity Insect age –Can greatly influence survival
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Insect issues….cont. Insecticide susceptible strain? –Where to get one? –What is your testing interest? LD-50 or Resistance Ratio (RR) Colony? –Who keeps one for your insect? –Use WHO standard? No Susceptible comparison…. –Reduces comparative values –Alright if using a diagnostic dose?
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Testing methods - Direct vs. Indirect Direct –Microapplicator Tiny drop applied to individual insects Cumbersome - Most accurate –Dip method Insect submerged into a solution of known strength
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Testing methods - Direct vs. Indirect Indirect –Treated glass Most common and often best method –Treated organics Treating filter papers, cloth, wood May have adsorption issues, especially formulated
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Treated Board Studies
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Holding patterns…. How long to expose insects to insecticide? –1 hr, 4 hr, 24 hr? –Irrelevant - pick one, dose will be adjusted When to count the dead? –Post-treatment count? OR –24 or 48 hr after exposure? Allows for kdr-resistant resistance detection.
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Resistance Profile vs. Diagnostic Dose Resistance Profile –Profile requires increasing doses Usually predates use of Diagnostic Dose Single dose or Diagnostic dose –Often used with formulated materials Label Rate or a Given level exposure Replication vs. Psuedoreplication –All steps must be repeated Includes weighing and mixing all solutions
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Analysis Control mortality –Critical Many blood-feeding Diptera survive poorly off host –Often use “Abbott’s Formula” Probit (logistic regression) –Generates mortality line –Used for Lethal Dose (LD) calculation Often used to identify 50% or 99% mortality value (% Mortality - % Control Mortality) (1 - % Control Mortality) = * 100
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Real-world Data House flies from 8 NY poultry and 4 dairy farms surveyed Many formulations tested –Multiple active ingredients Residual contact, feeding and larvicide assays Take home: Variations between sites, chemicals, methods, insecticide source….
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Experimental Compound
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Methomyl (Feeding)
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Dimethoate
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Tetrachlorvinphos
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Cyfluthrin
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Permethrin
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Permethrin
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Tetrachlorvinphos
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Dimethoate
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Ectiban EC
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Ectiban WP
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Which one to use? Needs based. To rapidly identify resistance –Field collected**** –Lab reared Precision –Technical**** –Formulated Deployed situations –Technical –Formulated**** Control failures –Technical –Formulated****
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www.who.int/whopes/resistance/en/ WHO - Test Kits
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Purchasing Kits
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Filth Flies
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