This is not unique to Singapore as pyrethroid resistance among Ae. aegypti has been reported in many countries. However, our study found that Ae. aegypti populations from historical make it clear and new dengue sensitive areas displayed no significant difference in their susceptibility to all insecticides tested. The results contradicted our hypothesis that the resistance level in historical sensitive areas would be higher than that in new sensitive areas because of more prolonged insecticide exposure in the former. Together with the previous findings of insecticide resistance, these results suggest that the mosquitoes from the newly sensitive areas could be due Inhibitors,Modulators,Libraries to migration of the vector from the historically sensitive areas. It is consistent with our observation that emergence of new dengue Inhibitors,Modulators,Libraries areas in Singapore is due to the geographical expansion of Ae.

aegypti on the island. Dispersal of already resistant mosquitoes due to human movement or goods movement could have contributed to the widespread pyrethroid resistance in Ae. aegypti throughout the country. This is in contrast to findings from Thailand and Africa where insecticide Inhibitors,Modulators,Libraries resistance appears to be focal and heterogeneous at short distances in different regions. Pyrethroids are broadly categorized into three groups based on their structure and toxicology type I, type II and non ester pyrethroid. Type II pyrethroids, which contain a cyano group, are more toxic than type I pyrethroids, and our study showed that type II pyrethroids had higher insecticidal activity than the Inhibitors,Modulators,Libraries type I pyrethroid.

Cross resistance among these pyrethroids, due to shared mode of action is well known. Aedes aegypti in Bandung, Indonesia displayed cross resistance between permethrin, and deltamethrin and was postulated to be due to these two types of pyrethroids sharing similar chemical structure. In Singapore, resistance Inhibitors,Modulators,Libraries to etofenprox was observed even though it has not been widely used. For example, it represents just 0. 17% of insecticides used in fogging by the private pest control industry during the period Jan 2009 to Sept 2011, contrasting with 56. 9% due to cypermethrin during the same period. Similarly, Kasai et al. reported that the high resistance of Culex pipiens to etofenprox was due to cross resistance from permethrin and phenothrin, as etofenprox is rarely used in Japan.

Helicoverpa armigera also exhibited cross resistance, selleck kinase inhibitor as it showed different levels of resistance to insecticides to which it had never been exposed. The cross resistance to insecticides with different chemical structure, such as in the case of non ester pyrethroid and II pyrethroids, suggest that these pyrethroids may target similar binding sites. In contrast to the high level of pyrethroid resistance detected, all populations of Ae. aegypti showed RR50 1. 01 to 1.