Larvicidal potential of different solvent extracts and oleanolic acid derivative from Coccinia indica against vector mosquitoes

The mosquito larvicidal activities of different solvent extracts (chloroform, ethyl acetate, and methanol) from the leaves of Coccinia indica were studied. Among the extracts tested, the methanol extract showed the highest larvicidal activity against early fourth instar larvae of Culex quinquefasciatus (LC₅₀?=?142?mg?L^?1), Aedes aegypti (LC₅₀?=?158?mg?L^?1) and Anopheles stephensi (LC₅₀?=?161?mg?L^?1) after 24?h of exposure period. The lowest larval mortality was observed with the ethyl acetate extract with the LC₅₀ values of 927, 872, and 730?mg?L^?1 against Cx. quinquefasciatus, Ae. aegypti, and An. stephensi, respectively. The chloroform extract showed the moderate larvicidal activity against the mosquito species tested with the LC₅₀ values from 446 to 546?mg?L^?1. A new triterpene was isolated from the methanol extract using bio-assay guided separation and identified as an oleanolic acid derivative by NMR, IR and mass spectral studies. The compound showed prominent larvicidal activity against Cx. quinquefasciatus, Ae. aegypti and An. stephensi with the LC₅₀ values of 5.6, 5.0, and 4.8?mg?L^?1, respectively. The results of the present investigation offer an opportunity for developing alternatives to rather expensive and environmentally hazardous organic insecticides.     

Evaluation of the larvicidal efficacy of extracts from three plants and their synergistic action with propoxur against larvae of the filarial vector Culex quinquefasciatus (Say)

Petroleum ether extracts of Piper longum, Curcuma aromatica, and Ocimum basilicum were tested for their larvicidal activity against Culex quinquefasciatus, a filarial vector using WHO standard procedures. Among the three plants, extract of P. longum was found to be highly effective with LC₅₀ and LC₉₀ being 0.89 and 1.49 ppm, respectively. C. aromatica also showed significant larvicidal activity with LC₅₀ and LC₉₀ being 11.41 and 17.36 ppm, respectively. The LC₅₀ and LC₉₀ for O. baslicum were 76.67 and 200.56 ppm, respectively. Propoxur, a carbamate was also studied for its larvicidal activity, which showed LC₅₀ to be 0.09 ppm and LC₉₀ to be 0.16 ppm. Synergistic studies of all three plant extracts with propoxur revealed P. longum as a more efficient synergist with synergistic factor (SF) of 4.13 for LC₅₀ value and 1.68 for LC₉₀. Both C. aromatica and O. basilicum exhibited antagonistic activity at their respective LC₉₀ values with propoxur. At 1 : 1 ratio of the phytoextracts and propoxur, P. longum and C. aromatica showed synergism whereas O. basilicum displayed additive effect. Thus, P. longum was found to be a better larvicidal and synergistic agent at all tested ratios. Evidence indicates that mixed formulations of phytoextracts with insecticides might reduce the concentration of the chemicals to be applied for vector control.     

Influence of some abiotic environmental factors on acute toxicity of inorganic lead to Cyprinus carpio var communis (Linn.) and Catla catla (Ham.) in simulated toxic aquatic environment

With the increase of water hardness from 60 to 720?mg/L CaCO₃, total alkalinity from 32 to 376?mg/L CaCO_3, pH from 7.6 to 7.9 and chloride from 28 to 350?mg/L, 96?h LC₅₀ on the basis of total lead increased from 8.2 to 1291?mg/L for Cyprinus carpio and 5.3 to 865?mg/L for Catla catla, when soil sediments were included these values were further raised to 1356 and 874?mg/L, respectively. The dissolved lead LC₅₀ values in all the treatments of soil and water was consistent with fixed amount of dissolved lead (1.04–1.78?mg/L) being needed for median lethal toxicity. Total lead toxicity also decreased with increase in pH from 6.3 to 11.3. 96?h LC₅₀ values increased for common carp 15 to 631?mg/L and for catla, 8 to 355?mg/L. But dissolved lead toxicity was found to increase with the increase of pH from 6.3 to 11.3 for both common carp (LC₅₀, 3.53 to 0.24?mg/L) and catla (LC₅₀, 2.21 to 0.09?mg/L). Removal of dissolved Pb with increasing carbonate content, particulate matter and pH due to adsorption, precipitation or coprecipitation reaction, reduced the dissolved lead concentration and thus the total lead toxicity. Increase in toxicity of lead with increase of exposure time was the biological response of longer contact time and decrease in dissolved lead toxicity with decrease in pH was due to increase H⁺ ion competition.     

Laboratory and field evaluation of Metarhizium anisopliae for the control of Dengue vector,Aedes aegypti (Insecta: Diptera: Culicidae)

Biological control at the larval stages of development of mosquitoes is one of the techniques that afford a non-expensive, easy-to-use, and environment-friendly method for mosquito control. In this study, investigations were undertaken on microbial product to develop a strategy to control mosquito larval and pupal population in the lab and field. Highest larval mortality was evident in the lab with LC₅₀ and LC₉₀ at 0.25 and 0.5 at 24?h for Aedes aegypti. In the field study, to kill mosquito larval population resulting in 100% mortality of A. aegypti required 5 days duration. The dose-dependent mortality was calculated using a lethal time of approximately 1–5 days test period. The number of mosquito bites (%) (vectorial capacity) decreased at increasing concentration of fungal insecticide. Data indicate that the fungal pathogen interacting with mosquito larvae controlled mosquitoes in the lab and field.     

Temperature effects on the toxicity of four trace metals to adult spotted Babylonia snails (Babylonia areolata)

A study was conducted to determine the median lethal toxicity of four heavy metals on the marine gastropod Babylonia areolata. Median lethal toxicity tests were conducted to observe the sensitivity of this gastropod to metals and how variations in temperature might affect toxicity of test elements. Four heavy metals were used in the study. It was observed that the 96-hr LC₅₀ (in mg/L) for the different metals was found to be nickel (Ni) 33.53 (35.22–28.43), copper (Cu) 44.59 (46.43–41.53), cadmium (Cd) 21.53 (23.43–18.37), and zinc (Zn) 27.34 (28.81–24.24) at room temperature 24 °C. With temperature as a variable, median lethal concentration (LC₅₀) values were observed to increase from 22.41 mg/L at 10 °C to 27.34 mg/L at 28 °C and reduce to 18.43 mg/L at 30 °C and a further rise in toxicity was observed at 35 °C where LC₅₀ value was 12.7 mg/L as seen in the case of Zn. It was also observed that at 40 °C thermal and chemical toxicity overlapped as 100% mortality was observed in controls. This trend was noted in all metals for Babylonia areolata indicating that temperature played an important role in determining LC₅₀ values of toxicants.     

Acute toxicity of benzophenone-type UV filters and paraben preservatives to freshwater planarian,Dugesia japonica

Fourteen benzophenone-type UV filters and four paraben preservatives were selected to examine their acute toxicities on Dugesia japonica. The 48-h LC₅₀ values for planarians exposed to benzophenone-type UV filters can be ranked as oxybenzone?>?mexenone?>?5-chloro-2-hydroxybenzophenone?> 2,4-dihydroxybenzophenone?>?2-hydroxybenzophenone?>?dioxybenzone?>?benzophenone?>?2,2′,4,4′-tetrahydroxybenzophenone?>?4-hydroxybenzophenone?> 3-hydroxybenzophenone?>?4,4′-dihydroxybenzophenone?>?2,2′-dihydroxy-4,4′-dimethoxybenzophenone?>?2,3,4-trihydroxybenzophenone?>?sulisobenzone with a range from 0.9 to 145?mg?L^?1 with a similar sequence for the 96?h LC₅₀ values, ranging from 0.5 to 77?mg?L^?1. The 48 and 96?LC₅₀ values for planarians exposed to paraben preservatives can be ranked as butylparaben?>?propylparaben?>?ethylparaben?>?methylparaben. Among all the tested chemicals, oxybenzone was the most toxic and sulisobenzone the least toxic chemical to planarian at each exposure period. Most benzophenone-type UV filters are toxic to aquatic animals with 48?h LC₅₀ values less than 10 mg?L^?1, except for 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,3,4-trihydroxybenzophenone, and sulisobenzone. Because of their common occurrence in aquatic environment, more studies on aquatic toxicities of benzophenone-type UV filters and paraben preservativs are needed to provide important information to adequately assess their ecological risk.     

4种甲氧基丙烯酸酯类杀菌剂不同剂型对斑马鱼急性毒性效应

采用半静态法测定了4种甲氧基丙烯酸酯类杀菌剂原药及制剂对斑马鱼(Brachydonio rerio)急性毒性。结果表明,以实测浓度计,250 g·L~(-1)嘧菌酯悬浮剂对斑马鱼的96 h半数致死浓度(LC50)值为0.539 mg·L~(-1),急性毒性为高毒,95%嘧菌酯原药和50%嘧菌酯水分散粒剂对斑马鱼的LC50(96 h)值分别为1.09和1.21 mg·L~(-1),急性毒性均为中毒;98%啶氧菌酯原药和22.5%的啶氧菌酯悬浮剂对斑马鱼的LC50(96 h)值分别为0.0974和0.0972 mg·L~(-1),急性毒性均为剧毒;95%吡唑醚菌酯原药、15%吡唑醚菌酯悬浮剂和250 g·L~(-1)吡唑醚菌酯乳油对斑马鱼的LC50(96 h)值为0.0613、0.0549和0.0487 mg·L~(-1),急性毒性均为剧毒;95%醚菌酯原药和50%醚菌酯水分散粒剂对斑马鱼的LC50(96 h)值分别为0.468和0.702 mg·L~(-1),急性毒性均为高毒。这4种甲氧基丙烯酸酯类杀菌剂对斑马鱼均有较高风险,会对其他水生生物也存在潜在的风险。     

Uptake and toxicity of some pesticides on three freshwater fishes (Oreochromis niloticus,Clarias gariepinus and Chrysicthys nigrodigitatus)

Studies were carried out to determine the toxicity of some selected pesticides on fresh water fish in a tropical environment. The uptake of the pesticides lindane, pentachlorophenol (PCP), and propoxur, which are frequently used by farmers and industrialists were studied in concrete ponds at the University of Cape Coast, in Ghana. The fishes used for the study were Oreochromis niloticus, Clarias gariepinus, and Chrysicthys nigrodigitatus, and were obtained from cultured ponds in the Cape Coast District and Mankessim in the Central Region and Weija Dam, in the Greater Accra region of Ghana. Single high lethal concentration (SD) or acute treatment and cumulative/chronic (or multiple minor) lethal concentration (CD) treatment were employed in administering the pesticides to the fishes via water. Gas chromatograph (GC) Electron Capture Detector (ECD) analysis was done on the dead fishes to see the extent of ingestion. The LC₅₀ values obtained for lindane on the three fish samples were as follows: Chrysicthys?–?0.38?mg?L^?1; Oreochromis?–?0.42?mg?L^?1, and Clarias?–?1.2?mg?L^?1. Mortalities occurred in fish within 3–5 days of application. For the PCP on Chrysicthys, Oreochromis, and Clarias species the LC₅₀ values were 0.42, 0.32 and 0.64?mg?L^?1, respectively for over a 2–3 day period. For a three-time influx period of propoxur the LC₅₀ for Chrysicthys, Oreochromis, and Clarias, were 22.0, 30.40, and 45.04 (all in mg?L^?1), respectively. The results obtained indicated that the pesticides had adverse effects on the general growth and reproduction of fishes. Gonadosomatic indices also showed that the pesticides affected the development of the body, the gonads, and their reproduction.     

Toxicity of zinc,cadmium and copper to the shrimp Callianassa australiensis. I. Effects of individual metals

The acute toxicity of zinc, cadmium and copper to Callianassa australiensis (Dana) was evaluated in static tests. Each test lasted up to 14 d and LC₅₀ values were calculated for 4, 7, 10 and 14 d intervals. The toxicity of each metal increased with exposure time; thus the 4 d LC₅₀ values of 10.20, 6.33 and 1.03 mg l^-1 were considerably higher than the 14 d LC₅₀ values of 1.15, 0.49 and 0.19 mg l^-1 for zinc, cadmium and copper respectively. Toxicity curves reveal that none of the values were asymptotic, indicating that median lethal threshold concentrations were not reached for any of the metals. This suggests that 14 d is an insufficient time in which to complete meaningful, acute lethality tests for marine shrimps. Longer tests are necessary if lethal threshold concentrations are to be used with application factors to derive safe concentrations for the protection of C. australiensis.     

Toxicity of metals to tadpoles of the common Sunda toad,Duttaphrynus melanostictus

Tadpoles of the common freshwater Sunda toad, Duttaphrynus melanostictus (Amphibia, Bufonidae), were exposed for a 4-day period under laboratory conditions to copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb), nickel (Ni), iron (Fe), aluminum (Al), and manganese (Mn) at various concentrations. Mortality was assessed and median times of death (LT₅₀) and lethal concentrations (LC₅₀) were calculated. LT₅₀ and LC₅₀ increased with the decrease in mean exposure times and concentrations for all metals. LC₅₀ (96?h) for Cu, Cd, Zn, Pb, Ni, Fe, Al, and Mn were 0.03, 0.3, 4.2, 1.5, 8.8, 0.4, 1.9, and 39?mg?L^?1, respectively. Cu was the most toxic to D. melanostictus, followed by Cd, Fe, Al, Pb, Zn, Ni, and Mn (Cu?>?Cd?>?Fe?>?Al?>?Pb?>?Zn?>?Ni?>?Mn). Duttaphrynus melanostictus is similarly sensitive to these metals as other amphibian tadpoles.     

Acute toxicity of ammonia to a freshwater teleost,Labeo bata larvae

Ammonia toxicity tests were performed with Labeo bata (bata) larvae of three different size groups. One hundred percent survival of larvae (500.0?±?4.0?mg) was recorded when exposed to ammonia concentrations of 1.0–13.56?mg?L^?1 at 96?h of exposure. Bata larvae exposed to ammonia concentrations of 15.8–25?mg?L^?1 showed 10–74% mortalities. The 96?h LC₅₀ value for 200 (±5), 250 (±2) and 500 (±4) mg bata larvae were 11.5, 16.8 and 22.5?mg?L^?1 un-ionised ammonia concentrations, respectively. When fish were exposed to different doses of ammonia, behavioural changes immediately occurred even at the lowest dose. At first, the fish became hyperexcitable, the skin darkened and they showed an increased ventilation frequency, fish behaviour became normal, 24?h after exposure. A 96?h LC₅₀ value of un-ionised ammonia showed direct relationship with the increasing size of bata larvae.     

Acute and chronic toxic effect of lead (Pb) and zinc (Zn) on biomarker response in post larvae of Penaeus monodon (Fabricus, 1798)

Metal pollution produces damage to marine organisms at the cellular level possibly leading to ecological imbalance. The present investigation focused on the acute and chronic toxicity of lead (Pb) and zinc (Zn) by examining the effects of biomarker enzymes in post-larvae of Penaeus monodon (Tiger prawn). Antioxidant biomarker responses such as lipid peroxidation (LPO) and catalase (CAT) activity for Pb and Zn were determined following chronic exposure. Acute Lethal Concentration ₅₀ (LC₅₀) values observed in the study at 96?h for Pb and Zn at 5.77?±?0.32?mg?L^?1 and 3.02?±?0.82?mg?L^?1, respectively. The estimated No Observed Effect Concentration and Lowest Observed Effect Concentration values for Pb were 0.014 and 0.029?mg?L^?1 and that recorded for Zn was 0.011 and 0.022?mg?L^?1, respectively. Among the two metals studied, toxicity of Zn was found to be greater to P. monodon than Pb. The activities of antioxidant defense enzymes and total protein content differed significantly from control following exposure to both metals. Overall, the biomarker studies demonstrated that alterations in antioxidant enzymes and induction of LPO reflect the consequences of heavy metal exposure in P. monodon.     

Chemical composition and antifungal activity of Chelidonium majus extracts – antagonistic action of chelerythrine and sanguinarine against Botrytis cinerea

This study discusses the similarities and differences between the antifungal activity of Chelidonium majus L. extracts and chelerythrine/sanguinarine, the main alkaloids in these extracts, against the plant pathogenic fungus, Botrytis cinerea. The obtained data show that the Ch. majus L. extracts inhibit the growth of B. cinerea very effectively. The extracts activity is significantly greater than that of chelerythrine/sanguinarine standard solutions alone and it does not always reflect the total content of alkaloids in the extracts. It has been proved that B. cinerea exhibits very diverse resistance to chelerythrine and sanguinarine. The IC₅₀ values for chelerythrine and sanguinarine equal 5.41?mg/mL and 1.76?mg/mL, respectively. In the mixture the antifungal activity of chelerythrine and sanguinarine is antagonistic in the concentration dependent way. Based on the presented data it is not clear, however, which alkaloids present in the Ch, majus extracts at significantly lower concentration levels enhance the activity of chelerythrine and sanguinarine so that the extracts activity is considerably greater than that of both main alkaloids mixtures.     

A comparison of two methods to observe the effects of dual metal exposure to the chironomus larvae

A study was conducted to investigate the effects of metal mixtures on the Chironomus plumosus. Two methods of preparing the mixtures were used, the Toxic Unit (TU) method and the parts per million (PPM) + PPM method. A comparison was undertaken between the two methods to observe the ease with which (1) experiment could be conducted and (2) whether LC₅₀ values could be obtained. In this study, it was noted that the PPM + PPM method was an easier method to conduct metal mixture experiments as the LC₅₀ values could be easily calculated for individual metals and compared with the LC₅₀ values of metals obtained from single metal experiments. The findings showed that the LC₅₀ value for zinc (Zn) was more toxic for chromium (Cr) when it was reduced from 9.6 to 0.3 mg L^?1, with silver the LC₅₀ value became 3.6 mg L^?1, 4.5 mg L^?1 with nickel (Ni). In the PPM + PPM method, the LC₅₀ value for Zn was observed to be 10.2 mg L^?1 when in mixture with chromium, 23.8 mg L^?1 with silver, and 13.4 mg L^?1 with Ni. Changes in the 96 h LC₅₀ value were found to be significant for all metals.     

Comparative toxicities of 10 widely used biocides in three freshwater invertebrate species

Owing to their widespread use in wooden products, industrial products, cosmetics, and personal care products, biocides are frequently detected in wastewater and surface water. In this study, I examined the acute toxicities of 10 commonly used biocides, namely methylisothiazolinone, benzisothiazolinone, octylisothiazolinone, dichlorooctylisothiazolinone, iodopropynyl butylcarbamate, triclosan, azoxystrobin, pyraclostrobin, climbazole, and clotrimazole, in the water flea (Daphnia similis), freshwater planarians (Dugesia japonica) and green neon shrimp (Neocaridina denticulata). Among the 10 tested biocides, dichlorooctylisothiazolinone was the most toxic to both D. similis and N. denticulata, whereas pracolstrobin was the most toxic to Du. japonica. By contrast, the least toxic biocides for D. similis, Du. japonica, and N. denticulata were climbazole, iodopropynyl butylcarbamate, and methylisothiazolinone, respectively. The 48-h nominal LC₅₀ values of all the biocides, except for benzisothiazolinone and climbazole, in D. similis were mostly less than 1 mg/L. In addition, the 96-h nominal LC₅₀ values of all the biocides, except for methylisothiazolinone and iodopropynyl butylcarbamate, in Du. japonica was less than 1 mg/L. These results indicate the biocides with low LC₅₀ values are relatively toxic to freshwater organisms.     

Determination of types of interactions exhibited by binary mixtures of heavy metals tested against the hermit crab,Clibanarius africanus

Single and joint action toxicity of heavy metal compounds (ZnCO₃, CuSO₄ and CdSO₄) were carried out against the hermit crab, Clibanarius africanus in laboratory bioassays. On the basis of 96?h LC₅₀ values, CuSO₄ (96?h LC₅₀?=?0.03?mM) was found to be the most toxic followed by CdSO₄ and ZnCO₃ (96?h LC₅₀?=?0.24?mM) in decreasing order of toxicity. The evaluation of the metal compounds in mixtures of ZnCO₃–CuSO₄, ZnCO₃–CdSO₄ and CdSO₄–CuSO₄ in pre-defined molar ratios revealed that interactions between Zn–Cu and Zn–Cd test mixtures were in conformity with the models of antagonism (reduction in toxicity of constituent metals). The synergistic ratios (S.R.s) and relationship between observed/predicted 96?h LC₅₀ values (relative toxic unit, RTU) were consistently below 1, indicating antagonistic interactions. Analysis using isobolograms also indicated the interactions between the mixture components to be antagonistic. However, with regards to CdSO₄–CuSO₄ test mixtures, the interactions between these metals were mainly in conformity with the model of synergism. The S.R. and RTU values were largely above 1, indicating synergistic interactions. The importance of the joint action evaluations for the management and protection of aquatic ecosystems, particularly in the setting up of water quality criteria was discussed.     

Comparative larvicidal potential of different plant parts of Withania somnifera against vector mosquitoes in the semi-arid region of Rajasthan

Larvicidal potential of the extracts from different parts viz. green and red fruits, seeds, fruit without seeds, leaves and roots of Withania somnifera in different solvents was evaluated against larvae of Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important disease vectors prevalent in the semi-arid region. Experiments were carried out on late 3rd or early 4th instar larvae of these mosquitoes using standard WHO technique. 24 and 48 hr LC50 values along with their 95% confidence limits, regression equation, chi-square (chi2)/heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for whole green fruits in water, methanol and petroleum ether were 350.9, 372.4, 576.9; 115.0, 197.1, 554.6; 154.9, 312.0, 1085.0 while corresponding values for red fruits were 473.5, 406.4,445.2; 94.7, 94.5, 1013.0; 241.8, 535.0, 893.3 mg l(-1) for An. stephensi, Ae. aegypti and Cx. quinquefasciatus respectively showing that methanol extracts were more effective against anophelines as compared to culicines when whole fruits were taken. The 24 hr LC50 values as observed for seeds in acetone, methanol and petroleum ether were 188.1, 777.5, 822.5; 245.5, 769.0, 1169.0; 140.3, 822.9, 778.4 and for fruit without seeds were 80.2, 97.6, 146.6; 88.4, 404.4, 1030.0; 30.0, 44.5, 54.2 mg l(-1) for the above mosquito species respectively showing that extract of fruit without seeds were most effective in petroleum ether followed by acetone and methanol extracts. However, experiments conducted with methanol extracts of leaves and roots of this plant species did not show any appreciable larvicidal activity and a 20-40% mortality was observed up to 500 mg l(-1) of the extracts. Overall larvae of anophelines were found more susceptible as compared to culicines to all the extracts tested. Petroleum ether extract of fruit without seeds was found most effective against all the mosquito species showing that active ingredient might be present in this part of the plant species. The study would be of great importance while planning vector control strategy based on alternative plant derived insecticides.     

Effects of metal pollution in the monosodium glutamate production effluent on full exploitation and biological treatment

Monosodium glutamate (MSG) effluent was sampled from three MSG mills and 21 metal elements were measured with a inductively coupled plasma (ICP) Spectrometer. The total metal concentration of each MSG wastewater sample was 19192, 3190 and 3161 mg/L respectively. Compared with the water quality standard issued by the Chinese Government and the World Health Organization (WHO), some values were found to exceed the standards. The 24hr‐LC₅₀, 48hr‐LC₅₀, 72hr‐LC₅₀ and 96hr‐LC₅₀ to the fish Ctenopharyngodon idellus were 6.9%, 3.2%, 2.5% and 1.4% MSG wastewater individually. The specific growth rate for photosynthetic bacteria (PSB) Rhodopseudomonas sphaeroides was inhibited by the metals in MSG wastewater. Therefor the MSG wastewater should not be discharged into drinking, irrigation and fishery water systems, moreover it cannot be treated by general biological processes efficiently. How to develop an effective biotechnique for the utilization of organic pollutants in MSG effluent will also be discussed in this paper.     

Effect of Pb,Cd and Cu on survival and development of Culex quinquefasciatus (Diptera: Culicidae)

ABSTRACT

The present research aimed to determine the lowest levels of three heavy metals (Pb, Cd and Cu) to which the larvae of Southern House Mosquito, Culex quinquefasciatus are susceptible in water. The study also aimed to investigate the effects of these heavy metals on the development of Cx. quinquefasciatus at concentrations set by Pakistan Environmental Protection Agency (Pak-EPA) as permissible levels for liquid industrial effluents. The 2nd instar larvae of Cx. quinquefasciatus were exposed to different concentrations of Pb, Cd and Cu and their effects on oviposition preference, egg hatching rate and larval development were studied. The LC₅₀ values of Pb, Cd and Cu were 12.6, 6.3 and 2.6?ppm, respectively. Gravid female mosquito adults deposited a significantly lower number of egg rafts in containers containing 0.50?ppm Pb or 1.0?ppm Cu in water. Each of the heavy metals in water resulted in significantly (p?<?0.05) lower egg hatching rate, prolonged time to pupation, lower pupation rate, prolonged time to adult emergence, lower adult emergence rate and higher female to male ratio. It is concluded that the 2nd instar larvae of Cx. quinquefasciatus are susceptible to Pak-EPA permissible levels of Pb, Cd and Cu in municipal and liquid industrial effluents.     

Effect of Water Variables On Lead Tolerance in Postlarvae of Penaeus Indicus (H. Milne Edwards)

Lead tolerance in Penaeus indicus post-larvae (PL) was studied in relation to the water variables: salinity, temperature and pH. the LC₅₀ for 96 hrs was 7.22 ppm at ambient conditions of salinity (20%_o), temperature (29°C) and pH (7.2). the post-larvae were found to be sensitive to salinity variations with a significant (P < 0.05) low LC₅₀ values at lower (2%_o) and higher (29%_o) ranges. Though a decrease in LC₅₀ value was observed both at higher (45°C) and lower (10°C) temperatures, it was significantly (P < 0.05) low only at higher temperature indicating more toxicity. the LC₅₀ values also showed a significant (P < 0.05) decrease in acidic (pH 2.8) and alkaline (pH 11.0) conditions. the data indicate that lead toxicity increases in the PL of P. indicus with variations in the water variables.