[Residual effectiveness of temephos observed in a Mexican southeast city affected by dengue].

OBJECTIVE To study the effect of water extraction and renewal on the residual action of temephos applied at 1ppm to cement water-storage containers at home. METHODS The study was conducted in two stages: one, determination of the granular temephos effectiveness on wild Aedes aegypti populations in order to set the monitoring baseline; and second, the measurement of the mean rate of water extraction at home and its effect on the residual activity of temephos. RESULTS The effectiveness of granular temephos was CL95 = 0.095 ppm (IC95%: 0.079-0.118). As average, it was found that 69.2% of water stored in cement containers was daily used and renewed, which means significant dilution. For the purpose of simplifying the experiments on residual activity, water was extracted and renewed at a rate of 50% every day for 2 weeks. It was found that temephos effectiveness significantly declined from day 7 on after application. CONCLUSIONS This rate of water extraction under study has an important effect on the residual activity of temephos. If this rate and the CL95 of granular temephos are considered in estimating the dosing, positive effects on the control of Aedes aegypti and more likely on the occurrence of resistance will be attained.