The resistance to various insecticides from 4 major groups (organochlorine,
organophosphate, carbamate and pyretroid) was investigated in a field strain of Culex
quinquefasciatus from Baan Suan community, Nonthaburi province, Thailand by using a
standard World Health Organization susceptibility test. The Baan Suan strain was completely
resistant to DDT and highly resistant to deltamethrin, permethrin, fenitrothion and propoxur
but this strain was still found to be highly susceptible to malathion. This strain displayed high
resistance to cypermethrin since the result revealed that the resistance ratio of the 50% lethal concentration value (RR50) between the field and the laboratory strains (NIH strain) was 16. The study indicated that mosquitoes were resistant to almost all insecticide tested except malathion and this should be an alternative for Cx. quinquefasciatus control in this area. Moreover, Aedes aegypti, which is a main dengue vector in Baan Suan community was also tested with deltamethrin, permethrin and fenitrothion. The results showed that dengue
mosquitoes are clearly resistant to permethrin and tolerant to deltamethrin, but was 100%
susceptible to fenitrothion. The cause of insecticide resistance in Cx. quinquefasciatus may
be due to the continuous use of insecticide for dengue vector control programme in Baan
Suan community.