Background: Malaria still remains a public health problem in Iran. There are different vector control interventions
such as insecticide spraying. The present study was carried out to determine the susceptibility status of Anopheles
stephensi larvae to temephos as a national plan for monitoring and mapping of insecticide resistance
Methods: Eight different localities in two main malarious provinces were determined as field collecting sites. Mos- quitoes were collected from the field and reared in an insectray. Susceptibility assays were carried out according to
the WHO method. The laboratory reared susceptible Beech-Lab strain was used for comparison. Data were analyzed
using Probit analysis to determine LC50 and LC90 values.
Results: Susceptibility of An. stephensi to temephos indicated that the LC50 ranged from 0.0022 mg/l to 0.0141 mg/l.
Although all field strains were susceptible to temephos, considerable variations in temephos resistance ratios of field
strains were noticed from all the localities studied in comparison with the susceptible strain. A low level of resistance
ratio was noticed in An. stephensi populations except for the Chabahar strain (RR= 4.27 fold). All field-collected An.
stephensi populations exhibited homogeneity to the larvicide except for Bandar Abbas and Hormoodar village strains
(P> 0.05%).
Conclusion: Due to intensive use of temephos in the neighboring countries and occurrence of resistant to this insecticide
in the main malaria vector in the region, insecticide resistance gene may evolve in the populations of An.
stephensi. If temephos be applied as a larvicide it should be used judiciously for resistance management, as rotation
strategy