Insecticide-treated nets (ITN) are an effective tool to reduce the burden of malaria in Africa. To address questions concerning the sustained impact of ITN in the face of changing transmission intensity and spreading insecticide resistance a series of four entomological investigations was undertaken in Tanzania. / First, a longitudinal survey of vector populations at different altitudes was conducted in the Hai District, Kilimanjaro Region, Tanzania. Entomological parameters relevant to malaria transmission were measured. Vector densities and entomological inoculation rates decreased dramatically with increasing altitude. Seasonal variations in the host preference and resting behaviour of Anopheles arabiensismay influence malaria transmission and control. / Second, the insecticide susceptibility status of vector populations from agricultural sites in the Kilimanjaro Region was evaluated. Malaria vectors from six sites were highly susceptible to diagnostic concentrations of pyrethroid insecticides and DDT in susceptibility tests. Permethrin tolerance in populations of An. arabiensis from an irrigated rice-growing area was not directly related to agricultural use of insecticides. Synergist bioassays indicated the contribution of a metabolic oxidase-based mechanism to the observed resistance while the knockdown resistance (kdr) mechanism was not detected. Close monitoring of resistance development in this area is needed. / Third, the biological efficacy of ITN and the insecticide susceptibility status of mosquito populations from areas with long-term use of ITN were investigated. Data were compiled from national surveys and long-term ITN projects to examine trends in resistance development in Tanzania. Anopheles species were highly susceptible to ITN and diagnostic concentrations of pyrethroid insecticides, while 'nuisance-biting' Culex quinquefasciatus displayed low susceptibility to these compounds. Low efficacy of ITN against C. quinquefasciatus has implications for user acceptance of ITN. / Finally, a novel method for kdr genotyping was developed and evaluated. Sequence specific oligonucleotide probes (SSOP) were used to identify kdr mutations in Anopheles gambiae s.l. in a high-throughput enzyme-linked immunosorbent assay (ELISA) format. Evaluation of the method on field-collected specimens detected the leucine-phenylalanine kdr mutation in two individual An. arabiensis, raising implications for the geographic spread of kdr-based resistance. The novel SSOP-ELISA method is a useful tool for high-throughput screening allowing sensitive detection of insecticide resistance.

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