Robust cuticular penetration resistance in the common bed bug (Cimex lectularius L.) correlates with increased steady-state transcript levels of CPR-type cuticle protein genes

Abstract

Bed bug (Cimex lectularius L.) populations are increasing worldwide, with resistance to insecticides thought to be a major contributor. Several recent reports have documented widespread kdr-type mutations at the target site for pyrethroid insecticides, and there is substantial published evidence for metabolic resistance mediated through cytochrome P450-mediated oxidation. Here we report that resistance ratios for a bed bug strain collected in Richmond, VA, increase by three orders of magnitude when the route of insecticide treatment is changed from inoculation to topical. This increase suggests that reduced cuticular penetration plays a powerful role in bed bug resistance to insecticides. We identified 62 putative cuticle protein-encoding contigs from bed bug transcriptome data containing the Rebers and Riddiford consensus sequence. We classified these contigs as to CPR type, and compared the amino acid composition of the different types to that of the entire proteome. Quantitative PCR analysis indicated that many of these transcripts were substantially upregulated in resistant bed bugs, with some more than 20-fold higher than in the susceptible strain. These results suggest the possibility that thickening or remodeling of the bed bug cuticle may contribute to decreased insecticide penetration.