Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 8 1 2014 06 15 21 34 EN Ruhma Syed Department of Zoology, Lahore College for Women University, Lahore, Pakistan. Farkhanda Manzoor Department of Zoology, Lahore College for Women University, Lahore, Pakistan. Rooma Adalat Department of Zoology, Lahore College for Women University, Lahore, Pakistan. Abida Abdul-Sattar Department of Zoology, Lahore College for Women University, Lahore, Pakistan. Azka Syed Department of Zoology, Lahore College for Women University, Lahore, Pakistan. 2015 10 16 Background: The present study was designed to investigate the insecticidal efficacy of four different classes of in-secticides: pyrethroids, organophosphates, phenyl-pyrazoles and neo-nicotenoids. One representative chemical from each class was selected to compare the toxicity: deltamethrin from pyrethroids, Dichlorovinyl Dimethyl Phosphate (DDVP) from organophosphates, fipronil from phenyl-pyrazoles and imidacloprid from neo-nicotenoids. The objec- tive of this study was to determine which of these insecticides were most effective against American cockroach. Methods: These insecticides were tested for their LC50 values against Periplaneta americana under topical bioassay method, using different concentrations for each chemical. Results: Fipronil 2.5% EC was highly effective at all concentrations applied, while DDVP 50% EC was least toxic amongst all. One way analysis of variance confirmed significant differences between mortality of P. americana and different concentrations applied (P< 0.05). Conclusion: Locality differentiation is an important factor in determining the range of resistance between various localities, as all three localities behaved differently in terms of their levels of resistance. https://jad.tums.ac.ir/index.php/jad/article/view/253 https://jad.tums.ac.ir/index.php/jad/article/download/253/229