2.4. Adult bioassay experiments
2.4.1. Tarsal contact bioassays
The standard World Health Organization (WHO) procedures
were followed to determine susceptibility/resistance status of
adult mosquitoes [10]. Bioassays were conducted by means of tarsal
contact exposure of mosquitoes to insecticide impregnated papers
using WHO test kits. Adult female mosquitoes (2–3 day old)
were tested against the WHO discriminating dosages of DDT, malathion,
propoxur and permethrin. Batches of 10–20 mosquitoes
(depending on the availability) were exposed to insecticide
impregnated papers for 1 h at 25 ± 2 C and 80% relative humidity
(RH). Mortalities were recorded after a recovery period of 24 h. At
least five replicates (a minimum of 100 mosquitoes) were carried
out per insecticide/species/district. Control experiments were carried
out by exposing the mosquitoes to papers impregnated with
carrier oil alone. Data were considered only if the control mortalities
were less than 20%. If there were mortalities in controls, actual
mortalities were calculated using Abbott’s formula [11].