Vector mosquitoes are related with various diseases on human, such as malaria (Anopheles sinensis (L.), An. sinensis), Japanese encephalitis (Culex tritaeniorhynchus (L.), Cx. tritaeniorhynchus), yellow fever (Aedes albopictus (L.)), dengue hemorrhagic fever (Ae. albopictus) and filariasis (Ae. albopictus), as well as nuisance insect pests (Culex pipiens pallens Foskal, Cx. p. pallens). Continued and repeated use of conventional insecticides such as organophosphorus and carbamates, pyrethroids has often resulted in the widespread development of resistance and has undesirable effects on non-target organisms and environment. Particularly, widespread insecticide resistance has been a major obstacle in the cost-effective integrated vector management program.
In theRepublic of Korea (ROK), studies on mass vector mosquito control using insecticides were mainly carried out until 1970’s such as a fuselage-mounted ULV spray system to C-46 aircraft, effectiveness of ground aerosols ULV premiumsumihtion, a helicopter application of ULV Dibrom and residual toxicity of organophosphates in animal shelters for Japanese Encephalitis (JE) and Plasmodium vivax malaria vector mosquito control.
Regional insecticide resistance of vector mosquitoes has been annually evaluated since ,early 1980’s, the first detailed study on susceptibility of seven mosquito species to 13 organophosphorus insecticides revealed the DDT and lindane resistance of Cx. tritaeniorhyunchus. Marked annual and regional variations of insecticide resistance have been observed. In comparative resistance, the resistance ratios of various insecticides were compared among each other using two strains of vector mosquitoes that were collected from same locality. An. sinensis from Koyang-si in 1992 and 1981 demonstrated >100 folds and >3000 folds of higher resistance to DDT and to bio-resmethrin. An. sinensis from Paju-si in 2008 demonstrated 30 folds of higher susceptibility to fenthion than those collected in seven years ago. Cx. tritaeniorhynchus from Gwanju in 2010 and in 1992 showed >100 folds of higher resistance to pyrethroids. In comparative regional resistance monitoring, Cx. p. pallens from six localities in the ROK in 2008 and six geospatially-distant field Cx. tritaeniorhynchus strains in 2011 showed marked regional resistance variations. Field populations of Cx. tritaeniorhynchus from agricultural areas demonstrated extremely higher insecticide resistance to pyrethroids than those from non-agricultural areas. Cx. tritaeniorhynchus populations from rice paddies had been under heavy selection pressure due to pyrethroids, which were used for a long time to control agricultural pests in the localities.
These results indicate that careful selection and rotational use of these insecticides may results in continued satisfactory control against field populations of vector mosquitoes

• Kyu-Sik Chang(Department of Medical Entomology, Korea Center for Disease Control and Prevention)