Bioassay for Evaluating Insecticide Resistance in Mosquitoes

Insecticide resistance can be evaluated using bioassays. The two commonly used assays are the WHO cone assay and the CDC bottle assay.

The WHO cone assay involves attaching standard WHO plastic cones to the treated test wall and transferring five female mosquitoes into one cone with an aspirator. The mosquitoes are exposed to the treated surface for 3 minutes, and the number of immobilized mosquitoes is documented one hour after exposure.

The mortality rate is determined after 24 hours. The CDC bottle assay is similar, but instead of cones, bottles are used, and the mosquitoes are observed for 2 hours. The resistance is determined by the percentage of mosquitoes that die at the pre-determined threshold time during the 2 hours.

If resistance is confirmed, an intensity bioassay is conducted to measure the strength of resistance in the population. The synergist bioassay is then used to determine if the resistance is caused by metabolic or other mechanisms. If the mortality rate of the susceptible test is more than 90%, no synergist assays are needed.

Review questions:

• What are the two commonly used assays for evaluating insecticide resistance?
• How long are mosquitoes exposed in the WHO cone assay?
• How long are mosquitoes observed in the CDC bottle assay?
• What is the purpose of the intensity bioassay?
• What is the purpose of the synergist bioassay?