Línea básica de susceptibilidad y efecto sinérgico a los insecticidas malation y pirmifos-metil en adultos de Culex spp. Say, 1823 (Díptera: Culicidae) del municipio Mario Brice？o Iragorry del estado Aragua, Venezuela

we evaluated the response to the organophosphorus insecticides malathion and pirimiphos-methyl in field populations of adult culex spp. mario brice？o iragorry municipality aragua state. bioassays were carried out using the bottles treated with insecticides. the time-mortality determination allowed us to obtain the baseline susceptibility of the insecticides evaluated. diagnostic dose was defined as the lowest dose that kills the highest percentage of exposed insects. survivors after 60 minutes of exposure to these doses was considered as resistance criterion defining this time, as the threshold of resistance. the mosquitoes were resistant to malathion at concentrations 0.1; 1 and 5 μg/ml with values of tl100= 90; 90 and 75 minutes respectively and susceptible to pirimiphos-methyl at concentrations 1 and 5 μg/ml with values of tl100= 30 and 15 minutes respectively, was obtained at the concentration 0.1 μg /ml tl100= 75 which was not considered to be a low dose. the concentrations 5 μg /ml of malathion, 0.1 μg / ml of pirimiphos-methyl are suggested as a reference dose. resistance mechanisms were identified with the synergist piperonyl butoxide (pb) at concentrations of malathion 1 and 5 μg/ml with fs = 2 and 2.5 respectively. multifunction oxidase enzymes (mfo) play an important role in resistance to the insecticide malathion. the obtained results provide basic information for future monitoring programs of culex spp, if necessary, due to its importance as a pest of tourist environments and as a vector of filariasis (bacroftiosis) and west nile fever.