Insecticide resistant mosquito strains are maintained under selection pressure to preserve their resistant phenotype. Two to five-day-old pyrethroid resistant strains are routinely selected every 3rd generation with 0.05% deltamethrin papers using the WHO susceptibility bioassay [17 ]. Insecticide papers were purchased from the WHO facility at the Universiti Sains Malaysia (USM), Penang, Malaysia and used a maximum of 6 times. Selection was undertaken at the adult stage as the strains were primarily used to screen for adulticides. If the mortality was less than 10% after exposure then routine selection was extended to every 5th generation; if mortality rose above 10% from 5th generation selections, then testing reverted to every 3rd generation. Exposure times of 1 h for FUMOZ-R and Tiassalé 13, 2 h for VK7 2014 and 3 h for Banfora M were used to ensure at least 20% survival; all adults from the generation to be selected are exposed, with results scored from at least 100 individuals.
All strains are profiled annually against six insecticides, representing the major classes of insecticides currently used for mosquito control, to monitor the stability of their resistance phenotype. Two to five-day-old female mosquitoes are exposed to the WHO diagnostic dose of insecticides and mosquitoes are held in a cabinet maintained at 26 ± 2 °C and 80 ± 10% RH and under a L12:D12 h light: dark cycle until mortality rates were recorded 24 h post-exposure. All papers and test kits are supplied by USM (Table2 ). In 2016, the use of bendiocarb papers was discontinued due to inconsistent results and propoxur papers were introduced as a replacement for carbamate resistance profiling. Results from the profiling are interpreted according to the WHO test procedures for insecticide resistance monitoring [17 ] with Abbottʼs formula [18 (link)] used to adjust for control mortality when needed.
All strains are profiled annually against six insecticides, representing the major classes of insecticides currently used for mosquito control, to monitor the stability of their resistance phenotype. Two to five-day-old female mosquitoes are exposed to the WHO diagnostic dose of insecticides and mosquitoes are held in a cabinet maintained at 26 ± 2 °C and 80 ± 10% RH and under a L12:D12 h light: dark cycle until mortality rates were recorded 24 h post-exposure. All papers and test kits are supplied by USM (Table
Insecticide, concentration (%) and exposure time used for profiling
| Insecticide | Class of insecticide | % concentration | Profiling exposure time (h) |
|---|---|---|---|
| Permethrin | Pyrethroid type I | 0.75 | 1 |
| Deltamethrin | Pyrethroid type II | 0.05 | 1 |
| Fenitrothion | Organophosphate | 1 | 2 |
| Bendiocarb | Carbamate | 0.1 | 1 |
| Propoxur | Carbamate | 0.1 | 1 |
| Dieldrin | Organochlorine | 4 | 1 |
| DDT | Organochlorine | 4 | 1 |
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