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Insecticide susceptibility and resistance of Culex tritaeniorhynchus (Diptera: Culicidae) larvae collected from Gwangju, Republic of Korea

SHIN, E. Hyun, KIM, Hyun Kyung, PARK, Chan, LEE, Dong-Kyu, KANG, Hyesook, CHANG, Kyu Sik
Entomological research 2011 v.41 no.4 pp. 157-160
Culex tritaeniorhynchus, bifenthrin, chlorpyrifos, etofenprox, fenitrothion, fenthion, larvae, lethal concentration 50, mortality, permethrin, public health, pyrethrins, South Korea
The susceptibility of Culex tritaeniorhynchus collected from Gwangju, Jeollabuk Province, Republic of Korea (ROK) to insecticides was evaluated under laboratory conditions using ten insecticides (7 pyrethroids and 3 organophosphates) that are currently applied by local public health centers in the ROK. Based on the values of median lethal concentration (LC₅₀), Cx. tritaeniorhynchus larvae were most susceptible to chlorpyrifos (0.006 ppm), fenitrothion (0.022 ppm), fenthion (0.035 ppm) and bifenthrin (0.038 ppm), and were least susceptible to esbiol (1.722 ppm). In comparative resistance tests, the resistance ratios (RRs) of seven insecticides were compared among each other using two strains of Cx. tritaeniorhynchus that were collected from the same locality during 1992 and 2010. Culex tritaeniorhynchus demonstrated significantly increased RRs to pyrethroids over time, while demonstrating decreased RRs among the organophosphates. Among the pyrethroids, permethrin had the highest RR values of 182.1- and 833.3-fold differences, followed by etofenprox with RRs of 138.4- and 224.1-fold differences in values of LC₅₀ and concentration that produced 90% mortality (LC₉₀), respectively. Culex tritaeniorhynchus strains demonstrated the least amount of change in susceptibility to the organophosphates, chlorpyrifos, fenitrothion and fenthion with 0.020-, 0.019- and 0.001-fold differences in resistance ratios (RRLC₅₀), respectively.