Quinquefasciatus Larvae Research Articles

Exploring the bioactive potential leaves of Sphaeranthus indicus: Targeting immature stages of Aedes aegypti and Culex quinquefasciatus mosquito vectors through bioassay-guided screening and fraction isolation

Mosquito control is vital for combating mosquito-borne diseases, but concerns exist regarding the use of synthetic insecticides. This study aimed to explore eco-friendly alternatives derived from natural sources. The larvicidal, pupicidal, and ovicidal activities of various fractions obtained from the hexane leaf extract of Sphaeranthus indicus were investigated against two important mosquito vectors, Aedes aegypti and Culex quinquefasciatus. S. indicus leaves were extracted with hexane and column chromatography was performed with hexane, ethyl acetate, methanol, and their mixtures as eluents. Among the ten fractions (F1-F10) evaluated, fraction ‘F-4’ exhibited significant activity against third instar larvae, pupae, and eggs of both mosquito species, closely followed by ‘F-5’ . At a concentration of 10 ppm, ‘F-4’ achieved 100% mortality in larvae and displayed LC50 values of 5.08 ppm and 5.03 ppm for Ae. aegypti and Cx. quinquefasciatus larvae, respectively. The LC50 values for pupae were 6.12 ppm and 5.83 ppm for Ae. aegypti and Cx. quinquefasciatus, respectively. Regarding ovicidal activity, ‘F-4’ demonstrated percentages ranging from 63.2% to 64.8% against Ae. aegypti and Cx. quinquefasciatus eggs, respectively. These findings underscore the potent larvicidal, pupicidal, and ovicidal effects of fraction ‘F-4’ from S. indicus against the targeted mosquito species. Further research is warranted to identify the active compounds responsible for these effects and explore practical applications for sustainable mosquito control strategies.

Biogenic Synthesis of Zinc Oxide Nanoparticles Mediated by the Extract of Terminalia catappa Fruit Pericarp and Its Multifaceted Applications.

Zinc oxide nanoparticles (ZnO-NPs) were biosynthesized by using the pericarp aqueous extract from Terminalia catappa Linn. These NPs were characterized using various analytical techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet (UV) spectroscopy, dynamic light scattering (DLS), and scanning electron microscopy (SEM), and XRD studies of the nanoparticles reported mean size as 12.58 nm nanocrystals with highest purity. Further SEM analysis emphasized the nanoparticles to be spherical in shape. The functional groups responsible for capping and stabilizing the NPs were identified with FTIR studies. DLS studies of the synthesized NPs reported ζ potential as -10.1 mV and exhibited stable colloidal solution. These characterized ZnO-NPs were evaluated for various biological applications such as antibacterial, antifungal, antioxidant, genotoxic, biocompatibility, and larvicidal studies. To explore its multidimensional application in the field of medicine. NPs reported a potential antimicrobial activity at a concentration of 200 μg/mL against bacterial strains in the decreasing order of Streptococcus pyogenes > Streptococcus aureus > Streptococcus typhi > Streptococcus aeruginosa and against the fungi Candida albicans. In vitro studies of RBC hemolysis with varying concentrations of NPs confirm their biocompatibility with IC50 value of 211.4 μg/mL. The synthesized NPs' DPPH free radical scavenging activity was examined to extend their antioxidant applications. The antiproliferation and genetic toxicity were studied with meristematic cells of Allium cepa reported with mitotic index (MI index) of 1.2% at the concentration of 1000 μg/mL. NPs exhibited excellent Larvicidal activity against Culex quinquefasciatus larvae with the highest mortality rate as 98% at 4 mg/L. Our findings elicit the therapeutic potentials of the synthesized zinc oxide NPs.

The Antimicrobial and Mosquitocidal Activity of Green Magnesium Oxide Nanoparticles Synthesized by an Aqueous Peel Extract of Punica granatum

An aqueous extract of Punica granatum peel was used as a biocatalyst for magnesium oxide nanoparticle (MgO-NP) synthesis, which was characterized via UV-Vis spectroscopy, TEM, EDX, FT-IR, XRD, DLS, and zeta potential. Data showed the efficacy of the plant aqueous extract in forming spherical, crystalline-nature, well-arranged MgO-NPs with sizes in the range of 10–45 nm with average sizes of 24.82 ± 8.85 nm. Moreover, EDX analysis revealed that the highest weight and atomic percentages were recorded for Mg and O ions. The green synthesized MgO-NPs showed antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, E. coli, Pseudomonas aeruginosa, and Candida albicans in a concentration-dependent manner with clear zones in the range of 8.7 ± 0.6 to 19.7 ± 0.5 mm with various concentrations. Also, the MIC value was varied to be 25 µg mL−1 for Gram-negative bacteria, B. subtilis, and C. albicans and 50 µg mL−1 for S. aureus. Moreover, MgO-NPs showed high activity against the 3rd-instar larvae of Culex quinquefasciatus. The mortality percentages were concentration- and time-dependent. Data analysis showed that the highest mortality was 88.3 ± 3.2%, attained at a concentration of 100 µg mL−1 after 72 h. Also, all originated pupae were malformed and did not hatch to adults, with mortality percentages of 100% at all concentrations. Overall, the P. granatum-mediated MgO-NPs showed promising activity in inhibiting the growth of pathogenic microbes and the hatching of C. quinquefasciatus larvae to adults.

Expression, activity, and consequences of biochemical inhibition of α- and β-glucosidases in different life stages of Culex quinquefasciatus.

Mosquitoes have a wide range of digestive enzymes that enable them to utilize requisite blood and sugar meals for survival and reproduction. Sugar meals, typically derived from plant sources, are critical to maintain energy in both male and female mosquitoes, whereas blood meals are taken only by females to complete oogenesis. Enzymes involved in sugar digestion have been the subject of study for decades but have been limited to a relatively narrow range of mosquito species. The southern house mosquito, Culex quinquefasciatus, is of public health importance and seldom considered in these types of studies outside of topics related to Bacillus sphaericus, a biocontrol agent that requires interaction with a specific gut-associated α-glucosidase. Here we sought to describe the nature of α-glucosidases and unexplored β-glucosidases that may aid Cx. quinquefasciatus larvae in acquiring nutrients from cellulosic sources in their aquatic habitats. Consistent with our hypothesis, we found both α- and β-glucosidase activity in larvae. Interestingly, β-glucosidase activity all but disappeared at the pupal stage and remained low in adults, while α-glucosidase activity remained in the pupal stage and then exceeded larval activity by approximately 1.5-fold. The expression patterns of the putative α- and β-glucosidase genes chosen did not consistently align with observed enzyme activities. When the α-glucosidase inhibitor acarbose was administered to adults, mortality was seen especially in males but also in females after two days of exposure and key energetic storage molecules, glycogen and lipids, were significantly lower than controls. In contrast, administering the β-glucosidase inhibitor conduritol β-epoxide to larvae did not produce mortality even at the highest soluble concentration. Here we provide insights into the importance of α- and β-glucosidases on the survival of Cx. quinquefasciatus in their three mobile life stages.

Bioconversion of chicken feather wastes into value added bioactive peptide by Geobacillus thermodenitrificans PS41 strain

A need for an economically attractive method for feather waste utilization, lead us to research for a new effective technology assuring an outcome of valuable product. In this study, keratinase producing Geobacillus thermodenitrificans a bacterial isolate PS41 was used to convert feather waste into bioactive peptides. Feather peptide under 15 kDa had shown a maximum antioxidant activity and it was identified as radical oxygenase of Propionibacterium acne. The purified feather peptide from PS41 showed antibacterial activity, anticancer activity against human alveolar basal epithelial cells, and larvicidal activity against Aedes aegypti, Anopheles stephensi, and Culex quinquefasciatus larvae in comparison to non-targeted organisms like zebra fish embryo and brine shrimp. The wound healing rate was significantly higher in peptide treated groups in comparison to standard and control groups respectively. Peptide treated wound had exhibited promisingly complete healing after 5 days of treatment in cat fish model and after 12 days of treatment in wistar albino rat. Histological analysis on experimental animal model showed that the tissue regenerating efficacy of peptide was more than the standard.

Cellulose microcrystalline: A promising ecofriendly approach to control Culex quinquefasciatus larvae

The growing use of synthetic chemical compounds/substances in vector control of mosquitoes, associated with their adverse effects on the environment and non-target organisms, has demanded the development of eco-friendly alternatives. In this context, this study aimed to evaluate the larvicidal action of different cellulose microcrystalline (CMs) concentrations and investigate their toxicity mechanisms in Culex quinquefasciatus fourth instar larvae as a model species. Probit analysis revealed that the median lethal concentrations (LC50) for 24 h and 36 h exposure were 100 and 58.29 mg/L, respectively. We also showed that such concentrations induced a redox imbalance in the larvae, marked by an increase in the production of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS), as well as a reduction in the activity of superoxide dismutase (SOD) and catalase (CAT). Furthermore, different alterations in the external morphology of the larvae were associated with the ingestion of CMs. On the other hand, exposure of adult zebrafish (Danio rerio) to LC5024h and LC5036h for seven days did not induce any behavioral changes or alterations mutagenic, genotoxic, biochemical, or in the production of cytokines IFN-γ and IL-10. Thus, taken together, our study demonstrates for the first time that the use of CMs can constitute a promising strategy in the control of C. quinquefasciatus larvae, combining insecticidal efficiency with an “eco-friendly” approach in the fight against an important mosquito vector of several human diseases.

Hemp (Cannabis sativa cv. Kompolti) essential oil and its nanoemulsion: Prospects for insecticide development and impact on non-target microcrustaceans

Formulation development and non-target effect studies are two crucial steps for the registration of new botanical insecticides. Previous reports put in evidence the potential of hemp (Cannabis sativa L.) essential oil (EO) as a new candidate ingredient for developing green insecticides. However, the validation of its target and non-target effects after proper encapsulation is missing so far. In the current work, we investigated the insecticidal efficacy of the EO obtained from the hemp variety ‘Kompolti’, and we optimized its formulation development into a nanoemulsion (NE). The latter was assayed against larvae of Culex quinquefasciatus Say, a well-known vector of Wuchereria bancrofti Cobbold, avian malaria, and several arboviruses, such as Western equine encephalitis virus, St. Louis encephalitis virus, West Nile virus, and Zika virus. Considering the percentage of encapsulated EO (7.5% w/w), the developed NE showed mortality on Cx. quinquefasciatus larvae, in terms of LC50(90) values [72.2 (207.2) ppm], like those of pure EO [50.8(142.3) ppm]. Non-target toxicity experiments showed limited toxicity on the aquatic microcrustacean Daphnia magna Straus (i.e., mortality <16% after 48 h of exposure to the EO-based NE at the LC90 estimated on mosquito larvae). Considering that the LC50 values detected in this study are lower than those belonging to many EOs, and that the application at sublethal doses caused mortality between 39.1% and 40.8% as well as a reduction in mosquito fertility resulting in a reduction in natality of 40.4% and 45.1% for the EO and EO-based NE, respectively, both products may be considered as potential environmentally friendly and sustainable insecticides.

Isolation, Genomic, and Proteomic Characterization of a Novel Neotropical Strain of Bacillus thuringiensis with Mosquitocidal Activities

The combination of genomic and proteomic analyses is a useful tool for the study of novel Bacillus thuringiensis (Bt) strains, as these approaches allow the accurate identification of pesticidal proteins and virulence factors produced. Here, we isolated and evaluated the potential of a novel Neotropical Bt strain (TOD651) for controlling larvae of Aedes aegypti and Culex quinquefasciatus mosquitoes. Aiming for the full comprehension of the TOD651 larvicidal potential, we further evaluated the whole TOD651 genome and conducted the proteomic analysis of the TOD651 spore–crystal mixtures. Our results showed that Bt TOD651 similarly killed both A. aegypti (0.011 µg/mL) and C. quinquefasciatus (0.023 µg/mL) larvae, exhibiting similar potency to the commercial Bt strain. The genome sequence revealed that Bt TOD651 harbors cry11Aa3, cry10Aa4, cry4Aa4, cry4Ba5, cyt1Aa5, cyt1Ca1, cyt2Ba13, mpp60Aa3, and mpp60Ba3. The proteomic analysis revealed no expression of Mpp60Aa3, while all the other pesticidal proteins were expressed (Cry4Ba5 was more abundant than Cyt1Aa5). The expression of the Mppe showed the major proportions between proteases. The virulent factor neutral protease B and spore coat proteins were also expressed. The expression of relevant pesticidal proteins (e.g., Cry, Cyt, Mpp, and other pathogenic factors), whose actions can occur in a synergic relation, indicates that the biocontrol using Bt TOD651 may contribute to delaying the selection of resistant individuals.

Bioefficacy of ursolic acid and its derivatives isolated from Catharanthus roseus (L) G. Don leaf against Aedes aegypti, Culex quinquefasciatus, and Anopheles stephensi larvae.

The aim of the present study was to identify the active principle from Catharanthus roseus leaf using larvicidal bioassay against three mosquito species viz. Aedes aegypti, Culex quinquefasciatus, and Anopheles stephensi. Preliminary studies of the three successive extracts such as hexane, chloroform, and methanol against Ae. aegypti larvae showed that the chloroform extract was more active with LC50 and LC90 values of 40.09ppm and 189.15ppm respectively. Bioassay guided fractionation of the active chloroform extract resulted in the isolation of a triterpenoid (ursolic acid) as the active constituent. Three derivatives acetate, formate, and benzoate were prepared using this, and they were tested for their larvicidal activity against three mosquito species. The acetyl derivative was highly active against all the three species compared to the parent compound ursolic acid; the activities of benzoate and formate were higher than ursolic acid when tested against Cx. quinquefasciatus. This is the first report related to ursolic acid from C. roseus with mosquito larvicidal activity. The pure compound could be considered for medicinal and other pharmacological applications in future.

The phyto-compounds Fumaric acid, di(1-adamantylmethyl) ester and 2-Pentamethyldisilanyloxypentane Borne from Physalis longifolia Against Various Medical and Agronomic Pests

Objectives: To identify the major phytocompounds of Physalis longifolia leaf methanol extract and assess the ovicidal and larvicidal toxicity of target medical and agronomic pests of Aedes aegypti, Culex quinquefasciatus, Spodoptera litura and Helicoverpa armigera eggs and larvae. Methods: In this study, the phyto-compounds identification was made by GC-MS analysis. The selected phyto-compounds were applied towards eggs were tested various concentrations 4-16mg/ml and larvae were tested various concentrations 2- 200mg/ml of medical and agronomic pests. Overall mortality was examined using probit analysis to calculate LC50/LC90. Findings: The most common an Indian medicinal flora, Physalis longifolia leaf methanol extract and its derived major phyto-bioactive constituents Fumaric acid, di(1-adamantylmethyl) ester and 2-Pentamethyldisilanyloxypentane were authentically isolated by GCMS analysis. By phyto-chemical screening, more numbers of bio-active phytochemicals were occupied in high polar leaf extract. P. longifolia leaf methanol extract and its derived major phyto-bioactive constituents Fumaric acid, di(1-adamantylmethyl) ester and 2-Pentamethyldisilanyloxypentane were showed topper eggs toxicity above 90% which reached nearly 100% and the larval toxicity of LC50/ LC90 values were 11.01/18.73, 10.56/ 17.90, 14.19/ 26.59, 14.88/ 27.80 mg/ml and 10.91/ 18.75, 10.70/ 18.26, 15.77/ 29.29 and 14.86/26.55 mg/ml against the medical and agronomic pests of Ae. aegypti, Cx. quinquefasciatus, S. litura and H. armigera, respectively. Novelty: The biotoxicity of selected P. longifolia leaf methanol extract and its derived major phyto-bioactive constituents were well effective, environmental friendlier and produced least toxicity on non-target organisms. The medicinal flora, P. longifolia originated phyto-products could be a valuable farmer and ecofriendly bio-toxic weapon on medical and agronomic pests which promotelesser susceptible on non-target organisms. Keywords: Phytoproducts; Ecotoxicity; Physalis longifolia; Medical pest; Agronomic pest

Larvicidal Effects of Three Plant Ethanolic Extracts against Culex quinquefasciatus SAY. Larvae (Diptera: Culicidae)

Laboratory experiments were conducted to evaluate thelarvicidal activity of ethanol extracts from the leaves of three plantspecies: Ricinus communis L. (castor plant), Vinca rosea L. (vinca) andLantana camara L. (lantana). Each of three extracts was used at fiverates; namely, 250, 500, 1000, 2000 and 3000 ppm, against the 3rd instarlarvae of Culex quinquefasciatus SAY. Larval mortality percentages wererecorded 24 hours after treatment. The larvicidal effect of each extractwas compared with the standard larvicide temephos (Abate® ). The threetested extracts showed larvicidal effects at all rates. Castor extract had thegreatest larvicidal effect with the lowest LC 50 (323.0 ppm), followed byvinca and lantana extracts. These results suggest that the leaf extracts ofthe three plant species should be considered as promising larvicidesagainst Cx. quinquefasciatus larvae

Larvicidal Efficacy of Azadirachta indica, Ocimum gratissimum and Cymbopogon citratus Ethanolic Extracts against Culex quinquefasciatus Larvae

Background: Effective and repeated control use of synthetic insecticides has led to the development of resistance development in mosquitoes. This problem has resulted in the need for the development of new strategies for selective mosquito larval control. The present work investigated the larvicidal efficacy of Azadirachta indica, Ocimum gratissimum, and Cymbopogon citratus ethanolic extracts against Culex quinquefasciatus mosquitoes. Methods: Extracts of A. indica, O. gratissimum, and C. citratus were obtained using 80% ethanol after their leaves had been previously air-dried for about 3-4 weeks. Thereafter, the solvent was evaporated with a rota-ry evaporator to eliminate any solvents still present. Twenty-five samples (in four replicates) of 2nd-3rd in-star larvae of C. quinquefasciatus were exposed to various concentrations (20 mg/L, 40 mg/L, 60 mg/L, 80 mg/L, and 100 mg/L) of each leaf extracts using WHO standard procedures. Data obtained were analyzed using the Statistical Package for Social Sciences (SPSS) for Windows, version 14, and statistical differences among mortalities induced by the different concentrations were obtained using Analysis of Variance (ANOVA) at a 95% confidence level (P= 0.05) with the aid of GraphPad prism 8. Results: There was an increase in the mortality rates of C. quinquefasciatus larvae as the concentration of each of the three leaf extracts increased over 24 hours. Eighty mg/L ethanolic extract of A. indica gave a mortality rate of 96.10% (24±0.1) after 24 hours of exposure, 100 mg/L of the same extract of A. indica gave a mortality rate of 100% (25.0. ±0.0) which is significantly (P &lt; 0.05) higher than 96.1% (24±0.1) and 80.0 % (20.0±0.5) at the same conditions in C. citratus and O. gratissimum respectively. Eighty mg/L and 100 mg/L of ethanolic extract of C. citratus gave 51% (12.5±0.7) and 96.1% (24±0.1) mortality rates after 24 hours. However, ethanolic extract of O. gratissimum resulted in the least 80.0 % (20.0±0.5) motility rate of C. quinquefasciatus larvae with exposure to 100 mg/L concentration after a 24-hour duration of exposure. Conclusion: The study concluded that the ethanolic extract of A. indica was the most active, followed by that of C. citratus and then O. gratissimum. The extracts of A. indica, C. citratus, and O. gratissimum hold great larvicidal potential, and they are important tools that can be integrated into the Culex mosquito vector control programme

Native Wolbachia infection and larval competition stress shape fitness and West Nile virus infection in Culex quinquefasciatus mosquitoes.

Wolbachia transinfections established in key mosquito vectors, including Aedes aegypti are typically associated with pathogen blocking-reduced susceptibility to infection with key pathogens and reduced likelihood those pathogens are transmitted to new hosts. Host-symbiont-virus interactions are less well understood in mosquitoes like Culex quinquefasciatus, which naturally harbor Wolbachia, with pathogen blocking observed in some populations but not others, potentially due to innate differences in their Wolbachia load. In nature, mosquito larvae are often subject to developmental stresses associated with larval competition, which can lead to reduced body size and differential susceptibility to arbovirus infection. In this study, we sought to understand whether competition stress and Wolbachia infection in Cx. quinquefasciatus combine to impact host fitness and susceptibility to infection with West Nile virus. We reared Wolbachia-infected and uninfected Cx. quinquefasciatus larvae under three competition stress levels, increasing larval density without increasing the amount of food supplied. We then monitored larval development and survival, measured wing length and quantified Wolbachia density in adults, and then challenged mosquitoes from each treatment group orally with West Nile virus. We observed that high competition stress extended development time, decreased the likelihood of eclosion, decreased body size, and increased susceptibility to West Nile virus (WNV) infection. We also observed that Wolbachia infection reduced WNV load under low competition stress, and significantly improved the rate of survival for larval reared under higher competition stress. Consequently, our data suggest that native Wolbachia infection in Cx. quinquefasciatus has differential consequences for host fitness and susceptibility to WNV infection depending on competition stress.

Tree canopy cover affects basal resources and nutrient profiles of Aedes and Culex larvae in cemetery vases in New Orleans, Louisiana, United States.

Cemetery vases are important habitat for vector mosquito production, yet there is limited understanding on their food web dynamics and how they vary across environmental gradients. Tree cover is one factor that varies widely across cemeteries, and influence food webs by means of detrital inputs, temperature mediation, and light availability. Such information can be important for determining mosquito adult body size, fecundity, and competition outcomes, all of which may influence mosquito population and disease risk. This study evaluates the relationship between tree canopy cover and indicators of basal resources for Aede aegypti (L.), Aedes albopictuss (Skuse), and Culex quinquefasciatus (Say) larvae, such as stable isotopes (δ13C and δ15N) and nutrient stoichiometry in cemeteries of New Orleans, Louisiana (USA). Stable isotope values suggest that larvae feed directly on the Particulate Organic Matter (POM) suspended in the vase's water, and that POM composition influence the nutrient profiles of mosquito larvae. The POM of open canopy vases had higher δ13C values, than that of closed canopy vases indicating differences in relative proportion of basal carbon sources, with open canopy POM having a lower proportion of allochthonous carbon, and a higher proportion of authoctonous carbon. Accordingly, mosquito larvae collected from open canopy vases had higher δ13C values, and higher C:N than larvae from closed canopy vases. The results of this study show a shift in food web dynamics driven by canopy cover in cemetery vases that directly influence the nutrient profiles of mosquito larvae. The implications for mosquito ecology, and vector management are discussed.

Larvicidal and repellent efficacy evaluation of Calotropis procera against Aedes aegypti Linn and Culex quinquefasciatus (Diptera: Culicidae) mosquito species under laboratory condition

To evaluate the larvicidal efficacy of methanol extract of Calotropis procera the experiments were conducted against larvae of Aedes aegypti and Culex quinquefasciatus mosquito species. Third instar larvae of selected mosquitos species were exposed to various concentrations (50-200 ppm) and were evaluated in the laboratory. The morality observation of exposed larvae was recorded at 24 hrs. After treatment. LC values of the Calotropis procera leaf extract was determined following Probit analysis. The LC50 and LC90 values of Calotropis procera against Aedes aegypti and Culex quinquefasciatus larvae were recorded as 67.01, 95.92 and 138.49, 213.17 ppm, respectively. The Dhoop candle containg active ingredient Calotropis procera exhibited 80.00% and 67.92% repellency against Aedes aegypti and Culex quinquefasciatus mosquitoes, respectively. From the results it can be concluded the crude extract and Dhoop candle incorporating Calotropis procera offers an excellent potential for controlling and as well as repelling Aedes aegypti and Culex quinquefasciatus mosquitoes.

Seaweed Sargassum wightii mediated preparation of TiO2 nanoparticles, larvicidal activity against malaria and filariasis vectors, and its effect on non-target organisms

Malaria and Lymphatic filariasis are considered significant public health concerns in several countries. As a researcher, controlling those mosquitos using safe and eco-friendly insecticides is essential. Thus, we aimed to explore the potential use of seaweed Sargassum wightii for the biosynthesis of TiO2 NPs and evaluate its efficiency in controlling disease-transmitting mosquito larvae (using Anopheles subpictus and Culex quinquefasciatus larvae as model systems (in vivo)) as well as its potential effect on non-target organisms (using Poecilia reticulata fish as an experimental model). XRD, FT-IR, SEM-EDAX, and TEM carried out the characterization of TiO2 NPs. It evaluated the larvicidal activity against the fourth instar larvae of A. subpictus and C. quinquefasciatus. The larvicidal mortality was observed after 24 h of exposure to S. wightii extract and TiO2 NPs. S. wightii synthesized TiO2 NPs show excellent activity against A. subpictus and C. quinquefasciatus (LC50 = 4.37 and 4.68; LC90 = 8.33 and 8.97; χ2 = 5.741 and 4.531) mg/L respectively. The GC-MS results indicate the presence of some important long-chain phytoconstituents like linoleic acid, palmitic acid, oleic acid methyl ester, and stearic acid, among others. Furthermore, when testing the possible toxicity of biosynthesized NPs in a non-target organism, no adverse effects were observed in Poecilia reticulata fish exposed for 24 h, considering the evaluated biomarkers. Thus, overall, our study results reveal that biosynthesized TiO2 NPs are an effective and exciting eco-friendly approach to controlling the A. subpictus and C. quinquefasciatus.

Insecticidal activities of Streptomyces sp. KSF103 ethyl acetate extract against medically important mosquitoes and non-target organisms

A potentially novel actinobacterium isolated from forest soil, Streptomyces sp. KSF103 was evaluated for its insecticidal effect against several mosquito species namely Aedes aegypti, Aedes albopictus, Anopheles cracens and Culex quinquefasciatus. Mosquito larvae and adults were exposed to various concentrations of the ethyl acetate (EA) extract for 24 h. Considerable mortality was evident after the EA extract treatment for all four important vector mosquitoes. Larvicidal activity of the EA extract resulted in LC50 at 0.045 mg/mL and LC90 at 0.080 mg/mL for Ae. aegypti; LC50 at 0.060 mg/mL and LC90 at 0.247 mg/mL for Ae. albopictus; LC50 at 2.141 mg/mL and LC90 at 6.345 mg/mL for An. cracens; and LC50 at 0.272 mg/mL and LC90 at 0.980 mg/mL for Cx. quinquefasciatus. In adulticidal tests, the EA extract was the most toxic to Ae. albopictus adults (LD50 = 2.445 mg/mL; LD90 = 20.004 mg/mL), followed by An. cracens (LD50 = 5.121 mg/mL; LD90 = 147.854 mg/mL) and then Ae. aegypti (LD50 = 28.873 mg/mL; LD90 = 274.823 mg/mL). Additionally, the EA extract exhibited ovicidal activity against Ae. aegypti (LC50 = 0.715 mg/mL; LC90 = 6.956 mg/mL), Ae. albopictus (LC50 = 0.715 mg/mL; LC90 = 6.956 mg/mL), and An. cracens (LC50 = 0.715 mg/mL; LC90 = 6.956 mg/mL), evaluated up to 168 h post-treatment. It displayed no toxicity on the freshwater microalga Chlorella sp. Beijerinck UMACC 313, marine microalga Chlorella sp. Beijerinck UMACC 258 and the ant Odontoponera denticulata. In conclusion, the EA extract showed promising larvicidal, adulticidal and ovicidal activity against Ae. aegypti, Ae. albopictus, An. cracens, and Cx. quinquefasciatus (larvae only). The results suggest that the EA extract of Streptomyces sp. KSF103 has the potential to be used as an environmental-friendly approach in mosquito control. The current study would serve as an initial step toward complementing microbe-based bioinsecticides for synthetic insecticides against medically important mosquitoes.

Phytochemical Screening and Comparative Larvicidal Activity of Albizia lebbeck and Tamarindus indica Leaf Extracts against Culexquinquefasciatus and Aedesaegypti

Different species of mosquitoes have been implicated in the transmission of various diseases to humans and livestock, including malaria, filariasis, dengue fever, encephalitis, etc. This study aimed to evaluate the in vitro larvicidal potentials of Albizia lebbeck and Tamarindus indica against the third instar larvae of two mosquito species, Aedes aegypti and Culex quinquefasciatus. Fresh leaves of the plants were collected, dried, grounded, and extracted separately with petroleum ether in a soxhlet apparatus. The powdered samples were screened for phytochemical constituents using standard methods. The larvicidal potential of both extracts was evaluated using the WHO protocols. Results of the phytochemical screening revealed the presence of alkaloids, glycosides, flavonoids, tannins, saponins, and triterpenoids. The extracts of both plants exhibited significant and dose-dependent mortality of C. quinquefasciatus larvae at 97.33% with LC50 of 0.3092 for A. lebbeck and 98.67%, with LC50 of 0.1729 mL/L for T. indica at extracts concentration of 1.6 mL/L. Also, the extracts showed significant and dose-dependent mortality of A. aegypti larvae with 25-92% mortality and LC50 = 0.2735 mL/L for A. lebbeck and 32-92% for T. indica leaf extracts with LC50 = 0.2889 µg/mL (p≤ 0.006621). We conclude that the extracts of these plants possess larvicidal potentials and could be developed into natural larvicides for mosquito control programs.

Assessment of susceptible Culex quinquefasciatus larvae in Indonesia to different insecticides through metabolic enzymes and the histopathological midgut

Filariasis and virus diseases that are transmitted by Culex quinquefasciatus are still a global health problem. Control of mosquito vectors with synthetic insecticides causes resistance to these mosquitoes to insecticides so that detection of susceptibility of the mosquito larval stage to insecticides is important for evaluating mosquito control programs. The aim of this study was to evaluate the susceptibility of wild-caught Cx. quinquefasciatus larvae in Jakarta, Indonesia, following exposure to temephos, malathion, cypermethrin, and deltamethrin; this was done by examining the detoxifying enzyme activities and histological damage to the larval midgut. Cx. quinquefasciatus larvae were collected from five fields in Jakarta and exposed for 24 h to temephos (1.25, 6.25, 31.25, and 156.25 ppm), malathion (0.5 ppm), cypermethrin (0.25 ppm), and deltamethrin (0.35 ppm). The larvae were then examined for acetylcholinesterase (AChE), glutathione S-transferase (GST), and oxidase activities using biochemical methods. Histological damage to the larval midgut was examined using routine histopathological methods and transmission electron microscopy (TEM). After 24 h, temephos and deltamethrin led to 100% mortality in the Cx. quinquefasciatus larvae. Temephos and malathion significantly inhibited the activity of AChE, while cypermethrin and deltamethrin significantly inhibited oxidase activity. Histologically, all insecticides damaged the larval midgut, as indicated by irregularities in the epithelial cell (ECs), microvilli (Mv), food boluses (FBs), peritrophic membranes (PMs), and cracked epithelial layers (Ep). The TEM findings confirmed that temephos and cypermethrin damage to the midgut ECs included damage to the cell membrane, nucleus, nucleoli, mitochondria, and other cell organelles. Overall, Cx. quinquefasciatus larvae in Jakarta were completely susceptible to temephos and deltamethrin. Synthetic insecticides may kill Cx. quinquefasciatus larvae through their actions on the metabolic enzyme activities and histopathological midgut.

Long-term storage does not affect the infectivity of entomopathogenic nematodes on insect hosts.

Entomopathogenic nematodes (EPNs) are effective biopesticides used in insect control. There are several formulations of entomopathogenic nematodes which are commercially available, but their popularity is low because the requirement of periodic release of stored entomopathogenic nematodes in field has reduced infectivity and is a constraint in large-scale repeated application of entomopathogenic nematodes in field. So, in order to overcome this impediment, the current study focuses on storage of entomopathogenic nematodes for a longer period of time using encapsulating beads. In this study, three EPNs, namely, Steinernema carpocapsae, Steinernema monticolum, and Rhabditis blumi, were encapsulated with Arabic gum and sodium alginate gel beads at different concentrations. Bio-efficacy of stored EPNs at different concentrations (50, 100, 200, 500, and 1000 infective juveniles (IJs)) in varying time intervals of 3, 6, 9, and 12weeks were tested against Culex quinquefasciatus larvae. The results show that, after 3weeks of storage, these entomopathogenic nematode species showed survival up to 96%, and in 12-week storage, survival rate was 50%. The virulence of the progeny that emerged from these stored entomopathogenic nematodes was similar to the fresh infective juveniles. The results of the present study show that Arabic gum-sodium alginate combination is a promising approach toward storing entomopathogenic nematodes. Furthermore, semi-field trials showed 70-90% larval mortality at a concentration of 3000 IJs (encapsulated and stored entomopathogenic nematodes in S. monticolum, S. carpocapsae, and R. blumi) on C. quinquefasciatus larvae. KEY POINTS: • Increased survival of stored EPNs (S. carpocapsae, S. monticolum, and R. blumi) in encapsulated gel using Arabic gum, sodium alginate, and yeast cells was assessed. • The efficacy was greater in stored EPNs at different concentrations from 3 to 12 weeks. • Semi-field trials of stored encapsulated EPNs are efficient in mosquito larval control.