Pyrethroid tolerance in Culex pipiens pipiens var molestus from Marin County, California

Abstract

In May 2001 a sample of Culex pipiens pipiens variety molestus Forskål from Marin County, California, collected as larvae and reared to adults, was found to show reduced resmethrin and permethrin knock-down responses in bottle bioassays relative to a standard susceptible Cx. pipiens quinquefasciatus Say colony (CQ1). Larval susceptibility tests, using CQ1 as standard susceptible, indicated that the Marin mosquitoes had LC50 resistance ratios of 18.3 for permethrin, 12 for deltamethrin and 3.3 for pyrethrum. A colony of Marin was established and rapidly developed higher levels of resistance in a few generations after exposure to permethrin as larvae. These selected larvae were shown to cross-resist to lambda-cyhalothrin as well as to DDT. However, adult knock-down time in the presence of permethrin, resmethrin and pyrethrum was not increased after increase in tolerance to pyrethroids as larvae. Partial and almost complete reversion to susceptibility as larvae was achieved with S, S, S-tributylphosphorotrithioate and piperonyl butoxide (PBO), respectively, suggesting the presence of carboxylesterase and P450 monooxygenase mediated resistance. Insensitive target site resistance (kdr) was also detected in some Marin mosquitoes by use of an existing PCR-based diagnostic assay designed for Cx. p. pipiens L mosquitoes. Carboxylesterase mediated resistance was supported by use of newly synthesized novel pyrethroid-selective substrates in activity assays. Bottle bioassays gave underestimates of the levels of tolerance to pyrethroids of Marin mosquitoes when compared with mortality rates in field trials using registered pyrethroid adulticides with and without PBO. This study represents the first report of resistance to pyrethroids in a feral population of a mosquito species in the USA.

Carboxylesterases in the Metabolism and Toxicity of Pesticides

“…with increased expression of esterase activity have now been reported (Anstead et al 2007;Guerrero and Barros 2006;McAbee et al 2004;Oakeshott et al 2005). In some cases the increased activity is due to specific CarbE isozymes, but in other cases several isozymes show more intense staining.…”

Phenotypic Variation among Culex pipiens Complex (Diptera: Culicidae) Populations from the Sacramento Valley, California: Horizontal and Vertical Transmission of West Nile Virus, Diapause Potential, Autogeny, and Host Selection

“…32,33,[38][39][40][41][42] Fonseca and others 30 found extensive hybridization (40%) between pipiens and molestus forms in the United States compared with European populations ( 10%), and a more recent study 42 found that autogenous populations in Santa Clara County, CA, were a genetic mix of f. molestus hybridized with Cx. quinquefasciatus and to a lesser extent f. pipiens.…”

Surveillance, insecticide resistance and control of an invasive Aedes aegypti (Diptera: Culicidae) population in California

“…A pyrethroidsensitive colony of Culex quinquefasciatus Say (CQ1), was used in one of the ULV trials as an additional pyrethroid susceptible control. The CQ1 strain was initially field-collected in Merced County, California, in the early 1950s and has been used at the Mosquito Control Research Laboratory, UC Davis as susceptible controls in insecticide bio-assays in the past (McAbee et al, 2004).…”