Resistance monitoring is routine testing of mosquito populations to detect changes in their susceptibility to the insecticides used to delay or prevent the development of insecticide resistance.
A. Larvicide Resistance
1. Evaluation of treatment efficacy may be
accomplished by monitoring the survival of contained larvae or monitoring larval densities before and after treatment using surveillance methods as in Section I. A. Larval mosquito surveillance above.
2. Dosage mortality bioassays are used to measure changes in lethal doses necessary to kill 50% (LD50) and 90% (LD90) of the population.
3. Biochemical microplate assays directly measure for esterases and oxidases, enzymes responsible for resistance, as well as the insensitive acetylcholine esterase altered target site mechanism. There is no microplate assay to detect the sodium channel altered target site mechanism.
4. Molecular tools such as Polymerase Chain Reaction (PCR) and real time RT-PCR measure increased copies of enzyme genes or mutations altering target sites.
1. Evaluation of treatment efficacy may be
achieved by monitoring pre and post treatment mosquito densities inside the control area using surveillance methods as in Section I. B. Adult Mosquito Surveillance above. Monitoring caged mosquitoes in the spray area may also be used to evaluate treatment efficacy.
2. Wind tunnel systems and other topical treatments provide data on changes in LD50 and LD90 levels.
3. Centers for Disease Control and Prevention (CDC) Bottle bioassays or World Health Organization (WHO) susceptibility bioassay kits can be used to test for resistance (see Appendix D for CDC & WHO websites). Bottle bioassays are easily combined with synergist to determine underlying mechanism(s).
4. Biochemical microplate assays directly measure for esterases and oxidases, enzymes responsible for resistance, as well as the insensitive acetylcholine esterase altered target site mechanism. Identification of resistance mechanisms helps determine cross-resistance spectrum and facilitates the choice of alternative insecticides.
5. Molecular tools work similarly on adults as they do on larvae.
1. The biologist/entomologist should routinely perform evaluations of treatment efficacy, as listed in A. 1 and B. 1 above. In addition, at least one of the other testing methods should be done regularly.
2. When resources are limited, universities or other established mosquito control districts may be contacted to assist with biochemical microplate assays and other susceptibility assays.
3. Inspector(s) should assist with field collections.
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