Efficacy of Gel Bait Insecticides with Different Modes of Action Against Pyrethroid-Resistant Blattella germanica...

The German cockroach, Blattella germanica (Linnaeus) (Blattodea: Ectobiidae), is a major urban pest that can cause allergic reactions and mechanically carry pathogenic microorganisms. Its control has become increasingly difficult because of widespread resistance to commonly used insecticides, particularly synthetic pyrethroids. This study compared the efficacy of six commercial gel bait formulations containing imidacloprid, dinotefuran, clothianidin, indoxacarb, spinosad, or fipronil against four field populations of B. germanica from Antalya, Türkiye, previously characterized and routinely monitored as pyrethroid-resistant. Adult females, adult males, and nymphs were tested separately, and mortality was recorded at 24 h intervals over a 120 h exposure period. Mortality data were analyzed using one-way ANOVA followed by Duncan's multiple-range test, while univariate ANOVA was used to evaluate the effects of gel bait formulation, population, developmental stage, and exposure time. Mortality differed significantly among the tested formulations, populations, developmental stages, and exposure times (p < 0.001). The dinotefuran-containing formulation produced the highest and most consistent mortality across all populations and developmental stages. The indoxacarb-containing formulation also showed high efficacy, although mortality developed more gradually during the early observation periods. The formulation containing imidacloprid showed the lowest efficacy, whereas those containing clothianidin, spinosad, and fipronil produced intermediate and population-dependent responses. Nymphs were significantly less susceptible than adult females and males. Overall, the efficacy of the tested gel bait formulations was influenced by formulation, field population, developmental stage, and exposure time. These findings provide comparative efficacy data that may support the selection and rotation of gel bait formulations in resistance-aware management programs for B. germanica.