High Levels of Pyrethroid Resistance and Super-Kdr Mutations in the Populations of Tropical Bed Bug, Cimex Hemipterus, in Iran

Abstract

Background: Tropical bed bug, Cimex hemipterus, is an important ectoparasite causing various health problems. This species is mainly confined to tropical regions; however, insecticide resistance, global warming, and globalization have changed its distribution map. Molecular information on pyrethroid resistance, which is essential for the development of control programs, is unknown for C. hemipterus in expanded areas. The present study was designed to determine the permethrin resistance status, characterize the pyrethroid receptor sites in voltage-gated sodium channel (vgsc) gene and identify the resistance-related mutations in the populations of tropical bed bug in Iran. Methods: Live bed bugs were collected, and adults of C. hemipterus were selected for bioassay and molecular surveys. Bioassay was performed by tarsal contact with permethrin 0.75% in mixed-sex of samples. Conventional and quantitative TaqMan and SYBR green real-time PCR assays were conducted to characterize the vgsc gene and genotypes of studied populations. Results: In the bioassay tests, the mortality rates were in the range of 30.7-38.7% and 56.2-77.4% in 24 and 48 hrs, respectively. The knockdown rates of studied populations were in the range of 32.2-46.6% and 61.5-83.8% in the first and second days, respectively. The KT50 and KT90 values in the C. lectularius Kh1 strain were presented as 5.39 and 15.55 hrs, respectively. These values in the selected populations of C. hemipterus varied from 27.9 to 29.5 and from 82.8 to 104.4 hrs, respectively. Knockdown resistance ratios (KR50 and KR90) in these populations varied from 5.17 to 6.17-fold compared with those of the C. lectularius Kh1 strain. Fragments of vgsc gene with 355 bp and 812 bp were amplified. Analysis of sequences revealed the A468T substitution, kdr-associated D953G, and super-kdr M918I and L1014F mutations in all populations. Conclusions: The simple, specific/sensitive and rapid diagnostic assays developed in this study are recommended for detection of kdr/super-kdr mutations and frequency of mutant alleles. The presence of super-kdr mutations and high resistance to permethrin in all the populations necessitate the reconsideration of control approaches against C. hemipterus.