Insecticide Resistance Testing

What is Resistance?

Insecticide resistance has been defined as a genetic change in response to selection by toxicants that may impair control in the field.  Insecticide resistance is measured at the population level (proportion or percentage of individuals in the population expressing a resistance trait). It is important to NOMTRCB to be good stewards of the environment, human health and city resources by using the most effective products while preserving susceptibility in local mosquito populations. Product use decisions are based on trends or changes over time in the proportion of individuals with resistance traits from our test sites.

How Do We Test for Resistance?

We use a variety of laboratory and field tests to measure resistance in our mosquito populations.  Resistance testing protocols, designed to enhance coverage and consistency across the parish are deployed. The protocol includes: ten fixed testing sites assessed annually, and six rotating sites evaluated on a five-year cycle. We test 5 chemicals on mosquitoes from each site. Chemicals tested are pyrethroids: deltamethrin, sumithrin, and etofenprox; and organophosphates: malathion and naled. We regularly test Cx. quinquefasciatus for resistance to these five insecticides using reagents and protocols according to the CDC Bottle Bioassay Kit. 

We also regularly screen our mosquito populations for molecular insecticide resistance. We test our Ae. aegypti for two known knock-down resistance (KDR) mutations and our Cx. quinquefasciatus for one known KDR mutation.