Introduction: Dengue and chikungunya are anthroponotic virus infections transmitted by Aedes aegypti mosquitoes. These conditions affect large areas of the American continent, including Costa Rica. The recent introduction of Zika virus infection is a new challenge for health systems. Given the absence of antiviral treatment and vaccines, Aedes aegypti control is the only alternative to minimize the impact of these viral diseases. In Costa Rica chemical control of the vector is based on the use of pyrethroids (cypermethrin and deltamethrin) and the organophosphate larvicide temephos, hence the importance of detecting the emergence of resistance to these insecticides. Objective: Determine the level of resistance to temephos, cypermethrin and deltamethrin in three Aedes aegypti strains from the Caribbean region of Costa Rica, as well as the corresponding enzymatic detoxification mechanisms. Methods: Resistance to temephos, cypermethrin and deltamethrin was evaluated with larval bioassays. Groups of 20 larvae were exposed to 5 insecticide concentrations for 24 hours. Mortality ranged between 2 and 100 %. Each concentration was evaluated by means of five replications, and estimation was performed of the concentration causing 50 % lethality (CL50). The Rockefeller strain was used as susceptible control. Each strain underwent estimation of a 50 % resistance factor (RF50) for each insecticide. Whenever resistance was observed, the bioaasays were repeated with prior exposure of the larvae to piperonyl butoxide (PBO) and S.S.S. phosphotrithiate tributyl (DEF) to evaluate the corresponding detoxification mechanism. Results: None of the strains evaluated was resistant to temephos. Incipient resistance to cypermethrin was detected in strains Guápiles and Limón (CL50= 0.01022, RF50= 7.35 and CL 50= 0.01016, RF50= 7.30, respectively), whereas resistance to deltamethrin was detected in the Siquirres strain (CL50= 0.01973 mg/L, RF50= 12.64). In the above-mentioned cases resistance decreased when pre-treatment with PBO was provided, indicating the presence of detoxification mediated by the Cyt P450 monooxygenase system. Conclusions: Results show that temephos continues to be effective for larval control of Aedes aegypti in the main areas of the Caribbean region of Costa Rica. A warning is hereby given about the emergence of pyrethroid resistance, leading to the need to optimize monitoring processes and the implementation of other chemical control alternatives.
