Investigation of the relationship between the pH of the filtering water and the biological efficacy of the EC formulation on the house fly (Musca domestica)

In this study, the efficacy of biocidal products containing Cypermethrin (Asmetrin®) and Cyfluthrin (Ciftox®) as active ingredients against house fly (Musca domestica L.) populations was comprehensively investigated within the framework of the roles of dilution water pH level, contact time, and application timing on biological effectiveness. In the experiments, a dose of 0.025 g active ingredient (a.i.)/m² was used for Asmetrin® and 0.03 g a.i./m² for Ciftox®. Three different pH levels (5.5, 7.0, and 8.5) and three application times (initial, 48 hours, and 120 hours) were tested. Both local and susceptible house fly populations were evaluated for knock-down (KD) rates at 5, 10, 15, and 30 minutes post-exposure, as well as mortality rates at 24 hours post-exposure. The experiments were conducted in a factorial design with three replicates, and the data obtained were analyzed using multivariate analysis of variance (MANOVA). Statistical analyses revealed that all factors—contact time, application timing, pH level, insect population, and biocidal product—had significant effects on biocidal efficacy (p<0.05). Furthermore, various two-way and three-way interactions among these factors were also found to be statistically significant. The findings indicated that Asmetrin® exhibited higher efficacy under mildly basic conditions (pH 7.0–8.5), whereas Ciftox® was more effective under acidic conditions (pH 5.5). Both products achieved maximum efficacy under initial conditions; however, their effectiveness decreased at 48 and 120 hours due to residual effects. Notably, the knock-down rate peaked within the first 15–30 minutes of contact. Additionally, both products induced higher mortality rates in the susceptible population. Probit analysis results showed that the LT50 values (time to 50% knock-down) ranged widely from 3 to 27 minutes, indicating that the efficacy of the biocidal products varied significantly depending on pH and the biological susceptibility of the house fly. These data are critically important for optimizing application strategies. The results confirm that the pH value of the dilution water is a determining factor in the biological efficacy of EC formulations. In conclusion, this study demonstrates that pH level, application timing, and contact duration must be carefully managed to achieve optimal efficacy of biocidal products, providing a scientific for developing more effective and sustainable strategies for pest control in human living areas.