This study assessed the toxicity and flushing activity of 5 commercially available botanical and essential oil formulations against 3 strains of German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae): a susceptible laboratory strain (S) and 2 insecticide-resistant field strains (D and E). Three bioassays were conducted: continuous exposure to dry residues, direct spray application, and flushing. The direct spray assay yielded the fastest kill, with a median survival time (MST) of 1 min when strain S was exposed to Essentria at the high label rate, likely due to rapid dermal and spiracular uptake. In contrast, the continuous exposure assay produced slower mortality, with the longest MST (23.5 h) observed in strain D with the same Essentria treatment, indicating slower uptake from dry residues. Among all formulations, ExciteR exhibited the fastest action in continuous exposure, while EcoVia and Garscentria showed limited residual activity. Strain-dependent differences were evident, with resistant strains showing greater survivorship in both continuous exposure and direct spray assays. In flushing assays, Essentria and EcoVia achieved the highest flushing activity (up to 45% and 35%, respectively, at 1,000 µg/µl), defined as the proportion of cockroaches leaving the harborage within 10 min. Other formulations, including ExciteR and ER-22, showed low flushing action. Overall, botanical and essential oil formulations were most effective when applied directly for immediate kill. Residual and flushing effects were generally weaker, particularly against resistant strains. Under laboratory conditions with confined exposure, botanical and essential oil formulations caused significant mortality in susceptible and resistant German cockroach strains.
Ajibefun et al. (Tue,) studied this question.