Comparative Insecticide Uptake Characteristics of Chlorfenapyr Suggests an Additional Reason Why Bed Bugs (Hemiptera: Cimicidae) are so Difficult to Control

Abstract

Abstract Insecticides interact with biochemical sites, disrupting homeostasis, leading to moribundity and death. Considering this process of intoxication, investigating insecticide uptake ensures an understanding of exposure profile. This study evaluated insecticide uptake by bed bugs, Cimex lectularius L., as affected by time and formulation, and a comparative uptake by German cockroaches, Blattella germanica (L.). Insects exposed to chlorfenapyr residues from two Phantom insecticide formulations (i.e., Aerosol and Suspended Concentrate (SC)) were solvent extracted and analyzed by GC-ECD. Chlorfenapyr uptake by bed bugs significantly increased with time, but the rate of external chlorfenapyr adsorption between the two formulations was not significantly different. However, initial exposure and uptake to the aerosol-treated versus SC-treated surfaces were significantly greater by 2.7x. Absorption-rates of chlorfenapyr residues inside the insect, associated with internal insect tissues or exoskeleton-bound, were significantly lower compared with external adsorption, with aerosol and SC formulations accumulating at 4.8x and 14.4x less, respectively. An unexpected formulation effect occurred with aerosol-treated papers and aging of residues. A reformulation of the aerosol provided a greater adsorption of chlorfenapyr at 19.1x that of the original formula after 2 hr. External versus internal uptake of chlorfenapyr by cockroaches was inverse to that seen in bed bugs, with greater chlorfenapyr absorption. Obstructing cockroach mouthparts prevented an internal uptake of chlorfenapyr and provided a similar exposure profile to bed bugs. This work demonstrates a need to evaluate insecticide uptake with formulation and insect morphology to maximize dose, especially in such a morphologically and environmentally isolated insect as the bed bug.