Due to the growing public health and tourism awareness, Cimex hemipterus Fabricius (Hemiptera: Cimicidae) has gained a great interest in increasing reported infestation cases in tropical regions of the world, including Malaysia. Since the information on the molecular ecology and population biology of this species are tremendously lacking, the isolation and development of molecular markers can be used to determine its genetic structure. In this study, novel microsatellite primers isolated from enriched genomic libraries of C. hemipterus were developed using 454 Roche shotgun sequencing. Seven validated polymorphic microsatellite primers were consistently amplified and characterized from 70 tropical bed bugs collected from seven locations throughout Malaysia. The number of alleles per locus identified ranged from 6 to 14. Comparison of loci for overall and between population were done with mean observed and expected heterozygosity were determined at 0.320 and 0.814, 0.320 and 0.727, respectively. Polymorphic information criteria (PIC) valued the markers as highly informative as PIC >0.5. Overall population, they are possibly in Hardy-Weinberg equilibrium with loci Ch_09ttn, Ch_01dn, and Ch_13dn showing signs of a null allele. There were no scoring errors caused by stutter peaks, no large allele dropout was detected for all loci and showed no evidence of linkage disequilibrium. In conclusion, all seven molecular microsatellite markers identified can be beneficially used to gain more information on the population genetic structure and breeding patterns of C. hemipterus as well as the relationship of dispersal and infestation.
The surge in tropical bed bug Cimex hemipterus (Fabricius) (Hemiptera: Cimicidae) infestations has led to an increase in genomic studies. In this study, the population genetics and breeding patterns of 22 Malaysian populations were analyzed, including genetic differentiation and genetic distance. For seven microsatellite loci, the number of alleles varied from 6 to 14. The allelels per loci contrasted sharply between the overall population and within the populations. The average observed and expected heterozygosity was 0.280 and 0.828 for the overall population and 0.281 and 0.657 among the populations, respectively. Based on polymorphic information criteria, the markers with a value >0.5 were highly polymorphic. In the Hardy-Weinberg equilibrium, the loci of Ch 09ttn, Ch 01dn, and Ch 13dn of the overall population showed signs of a null allele. The stutter peaks caused no scoring errors; large allele dropouts were not detected for any loci; and a correlation imbalance was not indicated. The genetic differentiation among populations was moderate, with a coefficient of genetic differentiation (FST) of 0.144. The bed bug populations showed strong inbreeding, with highly positive coefficients of inbreeding (FIS). The molecular variation attributed to inbreeding was 83% within the populations, compared with 17% among the populations. The admixture individuals in STRUCTURE and neighbor-joining phylogenetic trees also indicated weak genetic structure in the geographical populations, suggesting moderate gene flows between populations. Thus, moderately active dispersion and human-mediated transport shaped the genetic structure of C. hemipterus populations in Malaysia.
Bed bugs [both Cimex hemipterus (F.) and Cimex lectularius L.] are highly resistant to pyrethroids worldwide. An important resistance mechanism known as 'knockdown resistance' (kdr) is caused by genetic point mutations on the voltage-gated sodium channel (VGSC) gene. Previous studies have identified two point mutations (V419L and L925I) on the VGSC gene in C. lectularius that are responsible for kdr-type resistance. However, the kdr mutations in C. hemipterus have not been investigated.
The worldwide resurgence of bed bugs [both Cimex lectularius L. and Cimex hemipterus (F.)] over the past two decades is believed in large part to be due to the development of insecticide resistance. The transcriptomic and genomic studies since 2010, as well as morphological, biochemical and behavioral studies, have helped insecticide resistance research on bed bugs. Multiple resistance mechanisms, including penetration resistance through thickening or remodelling of the cuticle, metabolic resistance by increased activities of detoxification enzymes (e.g. cytochrome P450 monooxygenases and esterases), and knockdown resistance by kdr mutations, have been experimentally identified as conferring insecticide resistance in bed bugs. Other candidate resistance mechanisms, including behavioral resistance, some types of physiological resistance (e.g. increasing activities of esterases by point mutations, glutathione S-transferase, target site insensitivity including altered AChEs, GABA receptor insensitivity and altered nAChRs), symbiont-mediated resistance and other potential, yet undiscovered mechanisms may exist. This article reviews recent studies of resistance mechanisms and the genes governing insecticide resistance, potential candidate resistance mechanisms, and methods of monitoring insecticide resistance in bed bugs. This article provides an insight into the knowledge essential for the development of both insecticide resistance management (IRM) and integrated pest management (IPM) strategies for successful bed bug management.