Detection of Permethrin Resistance in Aedes albopictus Skuse, Collected from Titiwangsa Zone, Kuala Lumpur, Malaysia

This study was conducted to determine permethrin-resistance status, the presence of knock-down resistance (kdr) alleles using the synergist piperonyl butoxide (PBO), and mixed-function oxidase levels in laboratory-susceptible, laboratory-permethrin-selected, and field-strain Aedes albopictus. Three methods were used–WHO larval bioassay, WHO adult bioassay, and enzyme microassay of oxidase. A consistent permethrin-resistance level was observed in the larval stage throughout three continuous generations of laboratory-strain Ae. albopictus (LC 50 = 0.20 mg/l). In the larval stage, the laboratory-permethrin-selected Ae. albopictus strain showed increased resistance over successive generations, while larval-stage field-strain Ae. albopictus showed a decreasing trend. Irregular patterns were observed in LT 50 values, resistance ratios (RR), and synergistic ratios (SR), for all Ae. albopictus strains, including laboratory strains. These results showed that all Ae. albopictus strains tested were heterozygous. Permethrin resistance in the field-strain Ae. albopictus developed faster than in laboratory-permethrin-selected strain. On the other hand, enzyme microassay results showed a correlation between LC 50 and LT 50 values, with oxidase levels in all Ae. albopictus strains tested. These results confirmed that oxidase and not the kdr mechanism confers resistance to permethrin in these mosquito strains.