Culex quinquefasciatus (Say.) is a common and abundant mosquito species that causes serious nuisance through its irritating biting and acts as the vector of Wuchereria bancrofti that causes filariasis (also called elephantiasis) in different parts of the world. Control of mosquitoes is important for the protection of people and livestock from mosquito-borne diseases and from their nuisance biting. The constant use of synthetic insecticides has resulted in the development of insecticide resistance in insect pests, contamination of the environment, and adverse effects on humans and other non-target organisms. Plant based insecticides are gaining attention as they are biodegradable, safe, eco-friendly and effective. Control of mosquito population through the application of natural predators is also highly appreciated as this approach is also ecofriendly and effective. During the present research, three native medicinal plants i.e., Chenopodium ambrosioides (Linn.), Chenopodium botyrs (Linn.) and Cymbopogon nardus (Linn.) were evaluated for their mosquitocidal activities. The whole- plant n-hexane extracts of C. ambrosioides, C. botyrs and C. nardus were evaluated for larvicidal, pupicidal, adulticidal, oviposition deterrence and adult emergence inhibition activities against Cx. quinquefasciatus. The n-hexane extract of C. ambrosioides whole- plant was found most effective against the larvae (LC50 against 4th instar larvae = 204.2 ppm), pupae (LC50 = 1154 ppm) and adults (KDT50 at 1.25 % concentration = 28.4 minutes, KDT50 at 0.138 mg/cm2 = 8.4 minutes). Therefore, this extract was subjected to fractionation through column chromatography. The fractions obtained (F1 to F3) were then tested for adulticidal activity. The F1 fraction caused 100 % adult mortality at 1.5 % concentration. This fraction was further subjected to fractionation through column chromatography and the resultant six subfractions (F1.1 to F1.6) were then tested for adulticidal activity. Two subfractions of F1 fraction i.e., F1.1 and F1.5 showed strong adulticidal activity. The LC50 values of subfractions, F1.1 and F1.5 were 0.133 mg/ml and 0.130 mg/ml, respectively. The n-hexane extracts of all the three plants showed oviposition deterrent activity. For example, during oviposition deterrent activity at 31.25 ppm, maximum percentage of effective repellence (% ER) was shown by C. botyrs (37.1±8.7 %) followed by C. ambrosioides (29.3±5.5 %) and C. nardus (13.4±1.3 %). Minimum oviposition activity indices (OAI) value was observed for C. botyrs (-0.3±0.1) followed by C. ambrosioides (- 0.15±0.03) and C. nardus whole- plant (-0.1±0). The n-hexane extracts of all the three plants also showed adult emergence inhibition activity. Significantly lowest EI50 (EI stands for emergence inhibition) value was exhibited by C. ambrosioides (EI50= 139.3 ppm) followed by C. botyrs (EI50=312.3) and C. nardus extract (EI50=515.2). The n-hexane extracts of C. ambrosioides, C. botyrs and C. nardus whole- plants showed no toxicity against non-target organisms i.e., Odonate nymphs (Ischnura elegans and Sympetrum decoloratum), fish (Ctenopharingodon idella) and mammal (domestic rabbit of Oryctolagus cuniculus species). Damselfly (order Odonata, sub order Zygoptera) and dragonfly (order Odonata, sub order Anisoptera) nymphs have the predatory ability and share habitat with the immature stages of mosquitoes therefore they can be considered good biological control agents against larvae of mosquitoes. During the present study, the nymphs of damselfly (Ischnura elegans) and dragonfly (Trithemis aurora, Pantala flavescens, Libellula fulva, Sympetrum decoloratum and Crocothemis servilia) showed predatory ability against Cx. quinquefasciatus 3rd instar larvae in the laboratory. Among these nymphs, P. flavescens nymph was found most efficient predator of mosquito larvae. A single P. flavescens nymph consumed 47.0 ± 5.1 Cx. quinquefasciatus 3rd instar larvae per day. Mosquito larvae and their predators (damselfly and dragonfly nymphs) that share the aquatic habitat face increasing environmental pressure due to increasing urbanization and human activities. Therefore, there is the requirement of study for understanding the levels of environmental pollutants to which mosquito larvae and their predators are susceptible. Mosquito (Cx. quinquefasciatus) larvae and their predators were exposed to different environmental pollutants to determine the lowest level of pollutants to which mosquito larvae and their predators are susceptible or to determine the highest level of pollutants which the mosquito larvae and their predators can tolerate. During the study of susceptibility of Cx. quinquefasciatus larvae to different inorganic nutrient pollutants, the minimum concentrations of ammonium (NH4+), nitrate (NO3–) and (PO4–3) that caused mortality of Cx. quinquefasciatus 2nd instar larvae for 48 hours exposure was 20, 100 and 300 ppm, respectively. The gravid female Cx. quinquefasciatus adults preferred to oviposit in containers containing 5 ppm NH4+, 45 ppm NO3– or 30 ppm PO4–3 solution but did not prefer to lay eggs in control container or containers having higher concentration of NH4+ (10 ppm), NO3– (90 ppm) or PO4–3(60 ppm). No significant effect of NH4+, NO3– or PO4–3 on egg hatching rate was observed. The larvae that existed in containers containing NH4+ (5 ppm), NO3– (45 ppm) or PO4–3(30 ppm) solutions reached earlier to pupal and adult stages. Maximum percentage of these larvae reached to pupal and adult stages. The adults emerged from these larvae showed significantly higher female to male ratio as compared to control adults (P<0.05). These findings show that the levels of NH4+(5 ppm), NO3– (45 ppm) or PO4–3 (30 ppm) recommended by WHO (2006) for wastewater reuse in agricultural irrigation are favorable for the survival and development of Cx. quinquefasciatus mosquito, however higher levels of NH4+, NO3– or PO4–3 are not favorable for the survival and development of Cx. quinquefasciatus mosquito. During the study of susceptibility of Cx. quinquefasciatus 2nd instar larvae to heavy metals, the minimum concentration of lead (Pb), cadmium (Cd) and copper (Cu) that caused mortality of Cx. quinquefasciatus second instar larvae for 48 hours exposure was 0.5 ppm, 0.3 ppm and 0.25 ppm, respectively. The gravid female Cx. quinquefasciatus adults did not prefer the 0.5 ppm Pb or 1.0 ppm Cu solution for oviposition. Exposure of Cx. quinquefasciatus 1st instar larvae to 0.5 ppm Pb, 0.1 ppm Cd or 1.0 ppm Cu resulted into prolonged time to pupation and time to adult emergence and increased female to male ratio. These finding show that the levels of Pb (0.5 ppm), Cd (0.1 ppm) or Cu (1 ppm) recommended by Pakistan EPA (1997) in municipal and liquid industrial effluents, are not favorable for the survival and development of Cx. quinquefasciatus mosquito. During the study of susceptibility of predators of mosquito larvae to inorganic nutrient pollutants, I. elegans, T. aurora and P. flavescens tolerated high concentration of ammonium (up to 50 ppm), nitrate (up to 150 ppm) and phosphate (up to 250 ppm) for seven days under condition of neutral pH and room temperature. P. flavescens was found least susceptible to these pollutants. During the study of susceptibility of predators of mosquito larvae to heavy metals, the nymphs of I. elegans, T. aurora and P. flavescens tolerated high level of Pb (up to 40 ppm), Cd (up to 40 ppm) and Cu (up to 10 ppm). P. flavescens was found least susceptible to these heavy metals. These levels of Pb, Cd or Cu which the odonate nymphs tolerated is far above the concentration to which odonate nymphs would be exposed in the field. During the study of susceptibility of I. elegans and T. aurora to agricultural insecticides, the nymphs were found most susceptible to lambdacyhalothrin but least susceptible to chlorpyrifos. The LC50 values of lambdacyhalothrin and chlorpyrifos against I. elegans were 0.004 ppm and 0.142 ppm, respectively. Similarly, the LC50 values of lambdacyhalothrin and chlorpyrifos against T. aurora were 0.005 ppm and 0. 257 ppm, respectively. From the findings of the study of mosquitocidal activities of plant extracts, it is concluded that the n-hexane extracts of C. ambrosioides, C. botyrs and C. nardus wholeplants exhibit appreciable mosquitocidal activities. These extracts exhibit no toxicity with non-target organisms i.e., damselfly and dragonfly, fresh water fish (grass carp) and mammal (rabbit). Among the three plants studied during the present research, the n-hexane extract of C. ambrosioides is most efficient in larvicidal and adulticidal activities. The F1 column chromatographic fraction of C. ambrosioides n-hexane extract exhibit strong adulticidal activity. Two subfractions of F1 fraction i.e., F1.1 and F1.5 exhibit strongest adulticidal activity against Cx. quinquefasciatus, suggesting the presence of mosquitocidal compounds in these subfractions. From the findings of the study of predatory ability of damselfly and dragonfly nymphs, it is concluded that the nymphs of I. elegans, T. aurora, P. flavescens, L. fulva, S. decoloratum and C. servilia have the predatory ability against Cx. quinquefasciatus larvae. The nymph of Pantala flavescens is the most efficient predator of mosquito larvae among all the nymph species tested. From the findings of the study of susceptibility of Cx. quinquefasciatus larvae to different inorganic nutrient pollutants, it is concluded that the levels of NH4+, NO3– or PO4– 3 recommended in effluents for wastewater reuse in agricultural irrigation by WHO (2006) are favorable for the survival and development of Cx. quinquefasciatus mosquito, however higher levels of NH4+, NO3– or PO4–3 are not favorable for the survival and development of this mosquito. From the findings of the study of susceptibility of Cx. quinquefasciatus larvae to heavy metals, it is concluded that the levels of Pb, Cd or Cu recommended by Pakistan EPA (1997) in municipal and liquid industrial effluents are not favorable for the survival and development of Cx. quinquefasciatus mosquito. From the findings of the study of susceptibility of predators of mosquito larvae to inorganic nutrient pollutants, it is concluded that I. elegans, T. aurora and P. flavescens can tolerate high concentration of NH4+, NO3–and PO4–3 under condition of neutral pH and room temperature. From the findings of the study of susceptibility of predators of mosquito larvae to heavy metals, it is concluded that I. elegans, T. aurora and P. flavescens nymphs can tolerate high level of Pb, Cd and Cu contamination in water. The level of Pb, Cd or Cu which the odonate nymphs tolerated is far above the concentration to which odonate nymphs would be exposed naturally in the field. From the findings of the study of susceptibility of predators of mosquito larvae i.e., I. elegans and T. aurora to agricultural insecticides, it is concluded that deltamethrin, cypermethrin, lambdacyhalothrin, chlorpyrifos, dichlorvos and acetamiprid are hazardous to predators of mosquito larvae at very low concentrations. The application of these synthetic chemical insecticides should be minimized and safe application in the areas adjacent to aquatic habitats must be ensured. Application of other methods of insect pest control such as integrated pest management should be encouraged." xml:lang="en_US