Pyrethroid Resistance In Cimex Lectularius (Hemiptera: Cimicidae) In Germany

Abstract:
The development of resistance against insecticides, which are primarily used for bed bug (Cimex lectularius) control, is considered to one of the main reasons for the worldwide expansion of this pest. This study provides evidence of the occurrence of resistance and the mechanisms associated with a decreased pyrethroid susceptibility of bed bugs collected in Berlin, Germany. In five of 20 bed bug field strains collected from infested apartments in Berlin, susceptibility to deltamethrin was determined in a filter contact bioassay. Maximum detected resistance ratio (Rr) was Rr>20 and considerably lower than reported from other countries. However, pyrethroid resistance was confirmed for the AS strain with Rr>20 in a simulated use-test. Pyrethroid resistance has been shown to be associated with the presence of the amino acid sequence exchanges V419L or L925I in voltage-gated sodium channel alpha-subunit gene as the target site of pyrethroids and an increased metabolic detoxification by cytochrome P450 enzymes. Pyrosequencing of genomic DNA fragments was performed in order to analyze the frequency of these polymorphisms in strains and field populations. The L925I exchange was present in 15 of 18 tested strains and populations with allele frequencies of up to 100%. Additionally, in one strain both males and females had the exchange V419L with allele frequencies up to 96%. Furthermore, each strain showed non-mutated, heterozygous and homozygous mutated bed bugs for the substitution L925I. Relative mRNA-expression levels of the four CYP-genes cyp397a1, cyp398a1, cyp4cm1 and cyp6dn1 were determined with reverse-transcription quantitative PCR (RT-qPCR) for seven bed bug strains. In four of seven strains a higher relative mRNA-expression level of cyp397a1 was detected. One strain showed higher mRNA-expression levels of cyp397a1 and cyp398a1.