Bottle Bioassay in Duval County

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Bottle Bioassay in Duval County

• Testing Insecticide Resistance of
• Culex quinquefasciatus to Dibrom

Marah S. Clark, Jacksonville Mosquito Control
Division
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Introduction

• Dibrom has been applied by aircraft for over 30
  years in Duval County
• Culex quinquefasciatus is a vector species
• Evidence suggests that aerial adulticiding is not
  efficacious in controlling Culex in Jacksonville
  (2004 CDC collections after aerial spray
  application)
• Is there any significant resistance by wild Culex
  quinquefasciatus to Dibrom?

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Procedure

• Review bottle bioassay protocol, including
  documentation on preparing Dibrom test solution.
• www.pherec.org/memoranda/procedure.html
• Collect and rear native mosquitoes.
• Collected in larval stage from select catch
  basins
• Reared using artesian well water and pulverized
  dog food
• Obtain Dibrom sample from chemical store on site.

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Appropriate Test Solution Concentration

• ACS grade acetone used to prepare the solution
• Specific gravity 1.7 grams naled/ mL Dibrom
• To maintain consistency with other districts, the
  test solution was prepared based on 14.1 lbs
  naled/gallon of Dibrom
• Diagnostic concentration 25 ug/mL

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Percent Mortality
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Concentration Changes

• Previous labels report 14.1 lbs of naled/gallon
  of Dibrom (Dibrom 14), 85 active ingredient.
• Existing label changed to 87.4 active ingredient
  (Dibrom Concentrate).
• Will the change in concentration for Dibrom
  negatively effect the bottle bioassay tests?
• Is it necessary to modify the standard protocol
  because of the label change?

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Previous Dibrom 14 Label

• Active Ingredient, by wt
• Naled 85
• Inert Ingredients 15
• Contains 14 pounds technical naled per gallon
  equivalent to 12.6 pounds of naled

• Note, density was not put on previous Chevron
  Ortho or Valent MSDSs

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Current Dibrom Concentrate MSDS

• MSDS released October 23, 2003

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Current Dibrom Concentrate MSDS

• MSDS released October 23, 2003

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Gas Chromatography

• To determine if the difference would impact test
  results, GC was performed in August by the PHEREC
  lab with the Dibrom sample from JAX used to
  prepare the test solution.
• 0.50 ug naled/mL sample run
• Sample read at 0.4451 ug naled /mL
• Difference deemed insignificant.
• The bottle bioassay is a qualitative test, not
  quantitative.

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Conclusions

• Culex quinquefasciatus collected in Jacksonville
  displayed uniform susceptibility to Dibrom
  concentrate
• Difference in concentration according to old and
  new label is insignificant in preparing test
  solutions
• Consistency of how the test is conducted is
  important to maintain statewide standards

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Next Question

• If resistance is not a problem, is correct
  concentration being applied for the area?
• What may be other causes that would prevent
  effective control?
• Mosquito behavior minimizes vulnerability
• Weather (humidity, wind, temp., etc.)
• Mission timing (dusk versus dawn)
• Aerosol equipment, technique

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Notes/Future Tests

• Bottle Bioassay results indicate resistance only.
  They will not point toward appropriate field
  application rates.
• Bottle concentration is 2 X LC95 and is designed
  to kill 100 of the test mosquitoes in 1 hour.
• Run pre- and post- season tests for resistance in
  Culex species to Dibrom.
• Run permethrin tests for Culex species pre- and
  post- season.
• Conduct Dose Response experiments using Log Dose
  Probit (LDP) to estimate appropriate
  concentrations for both Cx. nigripalpus and Cx.
  quinquefasciatus.

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Acknowledgements

• Dr. Jack Petersen, PHEREC laboratory
• Dr. Ruide Xue, Anastasia Mosquito Control
• Whitney Qualls, Anastasia Mosquito Control
• Dr. He Zhong, PHEREC laboratory

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Thank you