 JUSTIFICATION OF THE STUDY The district of Muleba has been subjected to IRS with pyrethroid lambdacyhalothrin every year for 5 years under the President Malaria Initiative PMI programme. The malaria vector Anopheles gambiae s.s. is predominant in Muleba region and shows high level resistance to pyrethroid insecticides 14. In World Health Organisation WHO resistance tests with the pyrethroid used for IRS, An gambiae s.s. showed levels of mortality ranging from 8 to 40, indicating a high frequency of resistance across the entire district. Mortality to permethrin, the pyrethroid used in the LLIN distributed during the UCC Olyset Net was only 22. Entomological studies by the present authors showed that the pyrethroid resistance mechanism kdr is almost 100 in the Muleba An.gambiae s.s. population and elevated levels of mixed function oxidases and non-specific esterases are involved in the detoxification of pyrethroids. The carbamate bendiocarb was selected by PMI as the new insecticide of choice for IRS in the region. Following two rounds of bendiocarb IRS in January and May 2012, resistance is fast emerging. WHO resistance tests with bendiocarb showed mosquito survival rates rising from 18 in November 2011 to 23 in May 2012 and to 69 in November 2012 14. The only insecticide to which An.gambiae shows full susceptibility 100 mortality is the organophosphate pirimiphos methyl, the proposed new IRS intervention. 