Stability of Resistance to Permethrin and Malathion in Mexican Populations of Aedes aegypti (Diptera: Culicidae) with Recommendations for Rotational Use1

(L.) (Diptera: Culicidae) management in Mexico primarily involves destruction of breeding sites and application of insecticides. There are many cases of field resistance and few studies on the instability of this phenomenon, despite its usefulness in management of this pest. The goal of this research was to estimate, under laboratory conditions, the stability of resistance to permethrin and malathion in 3 field-collected Mexican populations of Ae. aegypti. Early fourth-instar larvae were used for the bioassays according to the methodology of the World Health Organization (WHO). Initially, we estimated the level of insecticide resistance in F1 larvae. Then, each population was individually reared without selection pressure through 7 generations, and the insecticide response was monitored and compared with the susceptible New Orleans strain. The resistance response (RR95) to permethrin in the F1 generation varied from 53.8 to 267.9X at the LC95 level. In malathion, the RR95 of the F1 generation ranged from 5.6 to 10.5X. In most cases, the highest rate of resistance decline occurred from F1 to F2. The response to permethrin and malathion after 7 generations without selection pressure was similar to that observed in the susceptible reference strain.