An attempt was made to determine the discriminative dose of a number of pyrethroid insecticides for An. stephensi tested on blood fed adult female 1 or 2 days against two strains, i.e. India and Bandar Abbass laboratory species in 1998. The tests were carried out according to WHO standard method in lots of 25 adult mosquitoes in 4 replicates. India and Bandar Abbas species of An. stephensi were tested with insecticides permethrin 0.1% , 0.25%, 0.75% and 1%, deltamethrin 0.005%, 0.0125%, 0.025%, 0.05% and 0.1%, lambdacyhalothrin 0.01%, 0.025%, 0.05%, 0.1% and 0.2%, cyflothrin 0.005%, 0.0125%, 0.025%, 0.5% and 0.1%, etophenprox 0.1%, 0.25%, 0.5%, 0.75% and 1% in 60 min exposure. Based on the results, discriminative dose were calculated for the above insecticide respectively 0.25%, 0.025%, 0.025% and 0.5% for two species. According to the results, An.stephensi has similar susceptibility to pyrethroid insecticides.

Background: 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.Methods: 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.Results: 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 α-esterase activity of Imam and Bouali Cina Hospitals and susceptible strains were 6.941×10-4, 6.940×10-4 and 8.01×10-5 nmol/min/mg protein; the mean β-esterase activity in those strains were 5.8×10-4, 4.25×10-4 and 7.28×10-5 nmol/min/mg protein; the mean content of p450 in the above-mentioned strains were 5.64×10-6, 1.89×10-6 and 1.2×10-6 nmol/mg protein; the mean GST activity were 6.66×10-2, 0.102 and 5.72×10-2 μmol/min/mg protein, respectively.Conclusion: 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.

An investigation was carried out on permethrin-susceptible and resistant strain of malaria vector, An.stephensi. Efficacy of several pyrethroids such as permetrhrin, deltamethrin, lambdacyhalothrin, cypermethrin and cyfluthrin against this species showed that those with an ?-cyano group and dibromo substitutions were more toxic to sensitive strains than the other classes like permethrin. The ranking order of toxicity of pyrethroids was different for resistant strains. Evidence of enhanced mono-oxygenase activity and the synergism shown by piperonyl butoxide suggests that each resistant strain possesses a mono-oxygenasemediatedresistance mechanism responsible, at least in part, for pyrethroid resistance

Susceptibility levels of a lab strain of An. Stephensi to WHO standard papers of DDT 4%, dieldrin 0.4%, malathion 5%, permethrin 0.25%, lambdacyhalothrin 0.1%, cyfluthrin 0.1% and deltamethrin 0.025% were determined in our laboratory in 1999. Results showed that at the diagnostic dose of insecticides this species exhibited resistance to DDT and dieldrin with mortality rate of 54±2.5% and 30±2.5%, respectively. Malathion 5% caused 96±1% mortality. Permethrin killed 90±2% of the populations. Alpha-cyano groups of pyrethroids, e.g., deltamethrin, cyfluthrin and lambdacyhalothrin had highest efficacy, the mortality was 99.5±0.5, 100%, and 99±0.5% respectively. The results of irritability of this species to lambdacyhalothrin, permethrin cyfluthrin and deltamethrin revealed that lambdacyhalothrin had the most and deltamethrin the least irritancy effect. The average number of take offs/fly/minutes for lambdacyhalothrin and deltamethrin were 1.699±0.35 and 0.946±0.13%, respectively. For permethrin and cyfluthrin the equivalent values were 1.52±0.2 and 1.385±0.25, respectively.

The rational use of insecticides largely depends on a broad knowledge of the susceptibility and irritability levels of malaria vectors to currently used insecticides especially pyrethroids. In this study the susceptibility and irritability levels of Anopheles stephensi and An.culicifacies to DDT 4%,malathion 5%, propoxur 0.1%, deltamethrin 0.025%, lambdacyhalothrin 0.1%, cyfluthrin 0.1% and permethrin 0.25% were determined. Susceptibility and irritability tests on adult mosquitoes were carried out according to WHO methods. The results showed that An.stephensi was resistant to DDT 4% and mortality rates to this insecticide in Gavdary and Abtar areas were 64.2%±3.9 and 61.8%±4.36, respectively. An.stephensi was assumed susceptible to other insecticides. An.culicifacies was found susceptible to all the tested insecticides. The irritability tests carried out with pyrethroids exhibited that permethrin 0.25% had the highest irritancy effect against both species. Lambdacyhalothrin 0.1% and deltamethrin 0.025% had the least irritancy effect against An.stephensi and An.culicifacies, respectively. Average numbers of take offs/females/minute of An.stephensi to permethrin, deltamethrin, cyfluthrin and lambdacyhalothrin were 6.64±1.04, 3.11±0.67, 2.73±0.61 and 2.57±0.67, respectively. These figures for An.culicifacies were 2.24±0.37, 1.44±0.38, 1.59±0.35 and 1.46±0.5, respectively. Irritancy effect of pyrethroids should come in consideration while they are used for control of malaria vectors.