Permethrin-Induced Changes in Hemocyte Count and Cellular Immune Responses in Periplaneta americana

Objective: This study aimed to evaluate the effects of permethrin on knockdown, mortality, total hemocyte count (THC), and cellular immune responses in Periplaneta americana.Materials and Methods: Two doses of permethrin (1.25 mg/m² and 2.50 mg/m²) were administered via tarsal contact. Hemolymph samples were collected at 30 min and 2, 4, 6, 12, and 24 h post-exposure to assess THC and cellular immune responses using light microscopy. Knockdown and mortality were morphologically monitored throughout the experiment.Results: Knockdown increased progressively over time in both treatment groups, reaching 100% at 24 h in the 1.25 mg/m² group and as early as 1 h in the 2.50 mg/m² group. Mortality reached 100% within 24 h in both groups. THC values decreased significantly in permethrin-treated insects compared with the control, with the 2.50 mg/m² dose causing a more consistent and pronounced reduction across most time points. A temporary recovery in THC was observed at the 4th hour in the lower dose group, whereas a sustained suppression was maintained in the higher dose group. In addition, nodular and aggregation structures were observed in the hemolymph, indicating the activation of cellular immune responses. Permethrin exposure also induced marked morphological alterations in hemocytes, including irregular cytoplasmic spreading, membrane disruption, cellular swelling, and nuclear abnormalities. Furthermore, micronuclei were detected in some hemocytes at higher doses, suggesting potential genotoxic effects.Conclusion: Permethrin induces dose- and time-dependent toxic effects on hemocytes, leading to significant alterations in cellular immunity in P. americana and potentially affecting insect physiology.