Chlorfenapyr susceptibility monitoring in bed bug (Cimex lectularius L.) field populations from the United States

Insecticides are an important component of bed bug (Cimex lectularius L.) integrated pest management programs. Chlorfenapyr (Phantom®) is a widely used insecticide for bed bug control. Chlorfenapyr is a chlorinated pyrrole that disrupts mitochondrial oxidative phosphorylation, preventing the formation of ATP. Bed bugs have developed resistance to certain pyrethroid insecticides. Thus, if chlorfenapyr is continuously used, there is a risk of bed bugs developing resistance. However, studies evaluating chlorfenapyr susceptibility levels in bed bugs are lacking. Our goal was to develop a diagnostic concentration-based bioassay method for assessing chlorfenapyr susceptibility levels in field-collected bed bugs from the United States. Chlorfenapyr concentration-mortality data for the insecticide-susceptible Harlan strain was generated using the glass vial bioassay and filter paper bioassay methods. The data was analyzed using PROBIT function in SAS to determine LC99 (lethal concentration) diagnostic concentrations for each bioassay method. Statistical comparison PROBIT data for both bioassay methods revealed that the glass vial bioassay was more accurate for chlorfenapyr susceptibility monitoring. Screening of field-collected bed bugs using the diagnostic vial bioassay revealed that chlorfenapyr susceptibility levels varied significantly between strains. Approximately half of the nine bed bug field isolates tested at the diagnostic LC99 concentration exhibited chlorfenapyr susceptibility levels statistically similar to the Harlan strain, whereas the remaining strains showed significantly reduced mortality responses. This is the first study to report chlorfenapyr susceptibility levels in field-collected bed bug populations. Results are discussed in comparison to pyrethroid (bifenthrin) susceptibility levels and practicality of the diagnostic bioassay method professional use.