ABSTRACT
The German cockroach is an important household insect pest mechanically involved in transmission of a variety of diseases to humans. Different classes of insecticides have extensively been used for its control leading to insecticide resistance development. Hence, for an optimal control of this pest, the status and underlying mechanisms of insecticide resistance should be studied in this group of insects. Adult German cockroaches were collected from Imam and Bouali Cina Hospitals [Sari, Iran] and subjected to bioassay using jar test method. The results were compared to those of a susceptible laboratory strain. Biochemical assays of esterases, monooxigenases and glutathione S-transferase [GST] levels were undertaken on German cockroaches from Imam and Bouali Cina Hospitals and the results were compared to a susceptible laboratory strain. The LT50 values of the three strains were 20.24 +/- 2.2, 19.87 +/- 2.3 and 8.89 +/- 0.26 for permethrin; 19.3 +/- 3.05, 17.6 +/- 0.68 and 8.8 +/- 0.99 for deltamethrin; 19.64 +/- 2.9, 18.66 +/- 3.45 and 8.64 +/- 0.62 min for cypermethrin, respectively. The mean alpha-esterase activity of Imam and Bouali Cina Hospitals and susceptible strains were 6.941 x 10-4, 6.940 x 10-4 and 8.01 x 10-5 nmol/min/mg protein; the mean beta-esterase activity in those strains were 5.8 x 10-4, 4.25 x 10-4 and 7.28 x 10-5 nmol/min/mg protein; the mean content of p450 in the above-mentioned strains were 5.64 x 10-6, 1.89 x 10-6 and 1.2 x 10-6 nmol/mg protein; the mean GST activity were 6.66 x 10-2, 0.102 and 5.72 x 10-2 micromol/min/mg protein, respectively. The LT50 values and also the mean activity of all enzyme groups in field strains were significantly different from those of the susceptible strain, indicating a vigour tolerance to insecticides and pyrethroids in particular. Hence, insecticide resistance monitoring techniques should be put in place and also resistance management strategies and measures should be considered implementing in the area