CDC Bottle Bioassay

About Insecticide Resistance

The use of insecticides to kill mosquitoes that spread Zika, dengue, and chikungunya viruses, is one part of an integrated mosquito management program. Insecticides may be used by professionals and by homeowners. Insecticides can be applied by hand (indoor and outdoor sprays and foggers), by truck, or by aerial (airplane) spraying.

Over time and repeated use, insecticide resistance can occur in mosquito populations. Insecticide resistance is an overall reduction in the ability of an insecticide to kill mosquitoes. This means that, when used as directed, a product no longer works, or only partially works. Insecticide resistance can be product specific, or it can develop to a certain class(es) of product.

In order to delay or prevent the development of insecticide resistance in vector populations, integrated vector management programs should include a resistance management component (Florida Coordinating Council on Mosquito Control 1998). Ideally, this should include annual monitoring of the status of resistance in target populations to:

  • Provide baseline data for program planning and pesticide selection before the start of control operations.
  • Detect resistance at an early stage so that timely management can be implemented.
  • Continuously monitor the effect of control strategies on insecticide resistance.

Explore the Pesticide Resistance Monitoring Program.

How Insecticide Resistance is Measured

Monitoring for resistance in the vector population is essential and is useful in determining the potential causes for control failures, should they occur. CDC has developed an assay to determine if a particular insecticide active ingredient is able to kill mosquito vectors. The technique, referred to as the CDC bottle bioassay, is simple, rapid, and economical compared with alternatives. The results can help guide the choice of insecticide used for spraying.

Programs in the continental United States and its territories can order free Insecticide Resistance Kits by sending an email to and requesting an order form. Kits include bottles, insecticide, and manual.

How the Bottle Bioassay Works

  • A bottle is coated with a known amount of insecticide (diagnostic dose). Mosquitoes are then put into the bottle and observed for 2 hours.
  • Resistance is determined by the percentage of mosquitoes that die (mortality rate) at the pre-determined threshold time during those 2 hours. The test should be run for the entire 2 hours unless all mosquitoes have died earlier than the 2 hours.

Bottle Bioassay Threshold Times and Amounts

CDC has determined bottle bioassay threshold times and diagnostic doses for several species of mosquitoes. Using the suggested bottle diagnostic dosages, the threshold times for various susceptible colonies are provided below. The CDC entomology laboratory uses these threshold times and amounts for their bottle bioassays. The concentrations and cut-off times can be used as a starting point for determining diagnostic doses and threshold times for additional species if susceptible colonies or populations are available. Once developed, the test can be routinely used for insecticide resistance testing.

Bottle Bioassay Threshold Times and Amounts
Chemical Class Chemical Final Concentration/Bottle µg/bottle Ae. aegypti REX colony Ae. albopictus LC colony Cx. pipiens NY/Chicago colony Cx. tarsalis BFS/KNWR colony Cx. quinque SEABRING colony
100% Mortality Expected (minutes)
Carbamate Bendiocarb 0.5 30 30 TBD 45 60
Organophosphate Chlorpyrifos 20 45 45 90 60 45
Fenthion 800 TBD TBD 75 45 45
Malathion 400 15 30 45 45 45
Naled 2.25 30 30 45 45 45
Pyrethroid Alpha- cypermethrin 5 10 15 45 TBD 45
Bifenthrin 10 10 10 45 30 60
Deltamethrin 0.75 30 30 45 TBD 60
Etofenprox 12.5 15 30 15 60 30
Lambda-cypermethrin 10 15 TBD 30 TBD 45
Permethrin 43 10 10 30 30 30
Prallethrin 0.05 120+ 120+ 60 120+ 60
Pyrethrum 15 15 30 45 30 45
Resmethrin 30 5 10 15 10 30
Sumithrin 20 10 45 30 30 45
Tau-fluvalinate 18 30 30 30 45 45

Information for Aedes aegypti, Ae. albopictus, and four Culex species mosquitoes are provided for areas where these species may be co-circulating. Culex species mosquitoes are important vectors of other arboviruses such as West Nile virus, St. Louis encephalitis virus, and Western equine encephalitis virus, which are endemic in the United States.