Background: The German cockroach, Blattella germanica (L.), is an important health and economic pest. Due to the development of resistance to insecticides and medical and economic importance of German cockroaches in urban areas, researches have been focused on using environmental-friendly biopesticides. This study aimed to evaluate the contact toxicity of essential oils of Allium sativum L. and Citrus nobilis var. deliciosa (Ten.) Swingle against adults of B. germanica.

Materials and Methods: The plant essential oils were obtained using a modified Clevenger-type apparatus through hydro-distillation. Bioassays were conducted using essential oil impregnated filter papers, which were placed at the bottom of plastic containers. The A. sativum oil was applied in the concentration ranges of 0.19-0.36 and 0.09-0.17 ml/m², and the C. nobilis oil was applied in the ranges of 5.82-7.23 and 3.15-5.50 ml/m² on females and males, respectively.

Results: The results of probit analyses of mortality data after 24 hours indicated that mortality of cockroaches was increased with increasing oil concentration. The toxicity of A. sativum oil (with the LC₅₀ values of 0.12 and 0.26 ml/m² on males and females, respectively) was significantly higher than C. nobilis oil. Moreover, males were more susceptible than females to A. sativum and C. nobilis oils (2.24 and 1.58 times, respectively).

Conclusion: To have a healthy and safety environment, the use of environmental-friendly biopesticides including essential oils is suggested for integrated management of German cockroaches’ populations in urban areas.