The resistance to various
insecticides from 4 major groups (organochlorine,
organophosphate,
carbamate and
pyrethroid) 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.