Toxicity, synergism, residual control, and secondary killing potential of broflanilide in resistant German cockroach populations (Blattodea: Ectobiidae)

Novel active ingredients from new insecticide classes are urgently needed to complement existing control tools and support rotation strategies for effective resistance management in the German cockroach, Blatella germanica (L.) (Blattodea: Ectobiidae). Broflanilide is a novel meta-diamide insecticide that acts as a noncompetitive antagonist of γ-aminobutyric acid (GABA)-gated chloride channels. This study evaluated the toxicity and synergism, residual efficacy, and secondary transfer potential of broflanilide against field populations of German cockroach. The baseline toxicity of broflanilide in a laboratory-susceptible strain was determined, with LD50 = 0.015 μg/insect and LD95 = 0.030 μg/insect at 48 h post-exposure. Topical application of broflanilide achieved >90% mortality at 3× LD95 against most of the field populations resistant to pyrethroid, fipronil, and imidacloprid. Piperonyl butoxide (PBO) acted antagonistically across all populations, whereas diethyl maleate (DEM) showed variable effects. Residual assays demonstrated that broflanilide applied at 12.5 mg/m2 on plywood surfaces produced a performance index (PI) >90 within 7 d, caused complete mortality, and exhibited no repellency. Residual efficacy persisted for 90-120 d. Secondary transfer through necrophagy on cadavers exposed to treated surfaces yielded PIs of 39-90, indicating partial but inconsistent indirect mortality. Overall, broflanilide provides strong residual efficacy, non-repellency, and prolonged control of resistant German cockroach populations at low application rates. Given its novel mode of action and the apparent lack of P450-mediated detoxification, cross-resistance with conventional insecticides is expected to be minimal. Broflanilide represents a promising addition to insecticide resistance management programs for the German cockroach.