Dynamics of permethrin on mosquito nets used in the malaria control program in Honiara, Solomon Islands

Abstract

A total of 11,373 permethrin-treated common and Olyset^[○!R](Sumika Life-Tech Co., Osaka) nets was distributed to 64 villages from October 1993 to February 1996 for the Pilot Malaria Control Program in Honiara. To monitor the efficacy of the nets, the chemical and biological assays were made. The gas chromatographic analysis of 206 nets showed an average surface dose of 258.1mg per m^2 of net, and 46.6 and 37% to retain the entomologically and epidemiologically effective doses of 60 and 100mg/m^2,respectively. Olyset nets lost 76% of the surface dose of permethrin by one washing with soap, but regained 82% by exposing to strong sunlight. The bioassay suggested that under the natural context Anopheles farauti escaped from the entomologically effective net before taking up a lethal dose due to the repellency and irritancy. From the results, it is recommended washing nets without soap, timely retreating common nets with permethrin, and reactivating Olyset nets by exposing to strong sunlight.