Since last two decades, the excessive and broad spectral usage of pesticides has achieved remarkable momentum in agriculture dependant countries like Pakistan. Pesticides are undoubtedly considered as a group of toxic chemicals that are introduced into the environment; most of which include insecticides, herbicides, fungicides, rodenticides and fumigants. These toxic compounds have some residues which retain in environment and not only contaminate it, but also develop resistance in target organisms against these chemicals. Frequent and repeated application of insecticides generally reduces the effectiveness and it results in the development of resistance in target pest against these insecticides. In general case, when whole population of targeted pests is selected by killing the susceptible individuals, it usually results in the emergence of resistant strains.

Insecticides play an important role in the control of mosquitoes. Unfortunately resistance has been developed by many mosquito species. In the present study, biotoxicity of four insecticides from four major groups: neo-nicotenoids (imidacloprid 5% SC) phenyl-pyrazoles (fipronil 2.5% EC), pyrethroids (deltamethrin 2.5% SC) and organophosphates (DDVP 50% EC) were tested against Ae. aegypti and Cx. quinquefasciatus. Samples were collected from different localities to determine the susceptibility of both species against tested insecticides. Larval toxicity results were different for (KotLakhpat) KLP and (Lahore College for Women University Lahore) LCW for each insecticide. KLP sample was considered as reference samples because it was exposed to insecticides at a very low extent as compared to LCW samples. Regression analysis of variance showed significant positive trend in mortality of both species. Fipronil and imidacloprid were proved to be most toxic against Cx. quinquefasciatus and Ae. aegypti in KLP samples. Deltamethrin showed least efficacy against both localities representing its high tolerance and resistance against pyrethroids.