Abstract
Cytochrome P450-monoxygenase mediated resistance (P450) is a vital biochemical enzymatic system that metabolizes xenobiotics and endogenous compounds. My project aims to characterize this detoxification resistance mechanism to pyrethroids in the southern house mosquito, Culex pipiens quinquefasciatus. Cx. p. quinquefasciatus is distributed throughout the southern hemisphere and vectors the nematode that causes lymphatic filariasis1 , West Nile virus 2, St. Louis encephalitis virus, bird malaria pathogens and the nematode that causes dog heartworm3 . Worldwide, pyrethroids are the primary class of insecticides used to control mosquito populations, especially during epidemics. According to the World Health Organization, resistance is “the biggest single obstacle in the struggle against vector borne diseases.” The mechanisms of resistance to pyrethroids include the P450 monooxygenases and a mutation (called kdr) at the voltage sensitive sodium channel. Currently, the P450(s) that confers resistance to pyrethroids is unknown, and only a handful of fitness tests have been conducted on mosquitoes, none of which were associated with the P450 mechanism. Understanding this system will aid in vector control management practices to help delay the onset of resistance in field populations. To characterize the P450 mechanism, we have created a strain of Cx. p. quinquefasciatus that is isogenic (99.94% related) to a laboratory susceptible strain. This new strain (ISOP450) is 1,000-fold resistant to permethrin (a pyrethroid). ISOP450 contains the P450 mechanism and is susceptible at the kdr site. To further explore this mechanism my project will address the following objectives: 1. Determine the inheritance of the P450 mechanism, 2. Trace P450 genotype frequencies through time under a neutral condition and two conditions of environmental pressure (cold and selection with the organophosphate, temephos), 3. Determine the structure activity of the P450(s), 4. Investigate the interaction with kdr, 5. Identify the over expressed P450(s) using proteomics, 6. Determine fitness costs using life table parameters, 7. Create a model based on the observed genetics, and 8. Conduct a population genetics study to determine P450 frequencies in field populations and relate those frequencies to those of other resistance mechanisms.
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1. WHO. (1957). Expert Committee on Insecticides, 125.
2. CDC. (2002). Provisional Surveillance Summary of the West Nile Virus Epidemic – United States, January-November 2002. MMWR 51(50):1129-1133.
3. James, M.T. and R.F. Harwood. (1969). Herms’s Medical Entomology. Sixth edition. The MacMillian Company: London. 484 pages.
