laboratory evaluation of toxicity of insecticide formulations from different classes against american cockroach (dictyoptera: blattidae).

b a ckground: 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.