Culex pipiens complex insecticide resistance

Insecticide resistance in and control challenges of Cx. pipiens s.l. in California (currently funded by multiple California Mosquito Abatement Districts and California Mosquito Research Foundation –

Since we discovered a population of Cx. pipiens  s.l. resistant to pyrethroids (Cornel et al 2000) we have followed up with ad hoc susceptibility testing. Most of our tracking efforts have focused on populations in Fresno County and resistance is quite widespread due to combined roles of kdr resistance and enzyme mediated detoxification (Waite et al. 2005, Inceoglu et al. 2009). ULV field trials inFresnoCounty, which have just been completed,   confirm that resistance to pyrethroids compromise efficacy of adulticides in urban residential areas and orchards. Resistance management strategies are now required to be developed and used in earnest for effective control of this important vector complex.

 Part and parcel of resistance management is to monitor for resistance and we have been engaged in multiple investigations with post docs and staff working in Bruce Hammock’s laboratory (Dept. Entomology and Nematology, UC Davis, http://www.biopestlab.ucdavis.edu/) to design high throughput sensitive and selective assays for detection of enzymatic/metabolic resistance (Kamita et al. 2011, Huang et al. 2012, Aman et al. 2012).

 Cornel, A. J., Stanich, M., McAbee, R. & Mulligan III. F. S. High level methoprene resistance in the mosquito Ochlerotatus nigromaculis (Ludlow) in Central California. Pest Management Science. 58: 791-798. 2002

 Inceoglu, A. B., Waite, T. D., Christiansen, J. A., McAbee, R. D., Kamita, S. G., Hammock, B. D. and Cornel, A. J. A rapid luminescent assay for measuring cytochrome P450 activity in individual larval Culex pipiens complex mosquitoes (Diptera: Culicidae). J. Med Entomol. 46 (1): 83-92. 2009.

 Waite, T.D., H. Huang, B. Inceoglu, J.S. Christiansen, R.D. McAbee, B.D. Hammock and A.J. Cornel.  Improved methods for identifying elevated enzyme activities in pyrethroid-resistant mosquitoes.  Proceedings of the 2005 Annual Mosquito and Vector Control Association of California Conference.  Vol. 73: 131-136. 2005.

 Kamita, S. G., Samra, A., Liu, J-Y., Cornel, A. J., Hammock, B. D. Juvenile Hormone (JH) esterase of the mosquito Culex quinquefasciatus  is not a target of the JH analog insecticide Methoprene. Plos One 6: (12) e28392. 2011.

 Huang, H., Yao, H., Liu, J.Y., Samra, A., Kamita, S. G., Cornel, A. J. Hammock, B.D. Development of pyrethroid-like fluorescent substrates for glutathione S- transferase. Analyt. Biochem. Doi:10.1016/j.ab.2012.09.011. 2012.

 Aman, S., Kamita, S., Hong-Wei, Y., Cornel, A. J., Hammock, H. B. Cloning and characterization of two glutathione-S-transferases from pyrethroid resistant ­Culex pipiens.

Pest Manag. Science. 68(5): 764-72. doi: 10.1002/ps.2324. 2012.

As mentioned earlier, not only have mosquitoes adapted to survive presence of xenobiotics (foreign chemicals) in the form of insecticides, they appear to, as is the case with Cx. pipiens s.l., have adapted to breed in underground trunk lines and storm drains in urban California. These sites are very difficult to treat because of unacceptability. This past summer we completed a evaluating an above ground trap kill system to try and reduce their numbers. We assumed that mosquitoes when given a choice would prefer to breed above ground but it appears from preliminary analyses that numbers were not impacted and that we will have to continue to work on developing monitoring and control strategies targeting the more inaccessible underground sources.