Techniques for Evaluating Insecticide Resistance in Filth Flies Resistance Profiles: Which Test To Use?

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Techniques for Evaluating Insecticide Resistance
in Filth FliesResistance 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
InsecticideApplication
InsecticideApplication
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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 oftenbest 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 Abbotts Formula
• Probit (logistic regression)
• Generates mortality line
• Used for Lethal Dose (LD) calculation
• Often used to identify 50 or 99 mortality value

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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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WHO - Test Kits
www.who.int/whopes/resistance/en/
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Purchasing Kits
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Filth Flies