Effective Mosquito Larvicides Research Articles

Phyto Fabrication of Silver Nanocomposites from Ageratum conyzoides as Potent Mosquitocidal and Antidengue Activity of Aedes aegypti

Mosquitoes pose an enormous threat to millions of people worldwide and transmit important diseases, including malaria, dengue, yellow fever, filariasis, Japanese encephalitis and the Zika virus. Currently, a growing number of phyto-synthesized silver nanoparticles (AgNPs) have recently been proposed as effective mosquito larvicides and are gaining traction over synthetic chemical pesticides due to their less deleterious effects on non-target species and novelty in mechanisms. action. The current study was conducted to evaluate the larvicidal and pupicidal activity of AgNP synthesized from Ageratum conyzoides against dengue vector Aedes aegypti as well as in vitro antiviral assay. The biosynthesized AgNPs were characterized using a UV-Vis spectrometer, powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The mosquito larvae were tested with biosynthesized AgNPs and the LC50 values recorded were I-stage (20.451), II-stage (23.307), III-stage (27.397), IV-stage (33.351), and pupa (39.668), respectively. To screen the anti-dengue properties of A. conyzoides-synthesized AgNP, an in vitro antiviral assay was performed. The present research reported moderate cytotoxicity rates in Vero cells exposed to A. conyzoides-synthesized AgNP at various concentrations. From this we observed that no adverse morphological differences were found in the treated cells that were comparable to the control Vero cells. Overall, our results demonstrated that AgNPs synthesized by A. conyzoides can be used to design newer and safer dengue control agents.

Novel effective mosquito larvicide DL-methionine: Lack of toxicity to non-target aquatic organisms

Mosquito larvicides are an effective tool for reducing numbers of adult females that bite and potentially spread pathogenic organisms. Methionine, an essential amino acid in humans, has been previously demonstrated to be a highly effective larvicide against four (4) mosquito species in three (3) genera, Anopheles, Culex and Aedes. The aim of the present study was to determine the potential impact on non-target aquatic organisms of methionine applied as a mosquito larvicide. DL-methionine concentrations ranging from 0.06% to 1.00% were used; wherein the highest concentration of 1.00% would result in 100% mortality within 48 h in mosquitoes. Acute toxicity assays were conducted in accordance with the US Environmental Protection Agency (US EPA) guidelines for the water flea (Daphnia magna Straus; Cladocera: Daphniidae) and the fathead minnow (Pimephales promelas Rafinesque; Cypriniformes: Cyprinidae). Water fleas and fish were placed directly into the solutions in glass containers and tanks for 48-hours and 96-hours, respectively. When applied within the above-mentioned range of effective mosquito larvicide concentrations, DL-methionine meets US EPA criteria as a "practically non-toxic" pesticide for both species. These results suggest that methionine is a viable alternative to current mosquito larvicide options, which are typically classified as moderately to highly toxic and may be a valuable addition to a mosquito integrated pest management program.

Methionine as an Effective Mosquito Larvicide in Natural Water Sources

Methionine is a naturally occurring amino acid that has demonstrated toxic properties for control of larval mosquitoes in laboratory experiments. Methionine offers many desirable qualities for an effective, biorational pesticide, including its minimal effects on non-target species. Because previous studies regarding this amino acid's toxicity were laboratory based, the next step is to establish if methionine is likely to have similar effects in natural water bodies before attempting costly field trials. Therefore, the goal of this study was to test the effectiveness of DL-methionine applied to various water sources. Concentration response experiments conducted in glass jars used larval Aedes aegypti (L.) (Diptera: Culicidae) as a model organism. Well, deionized, and pond water were evaluated in the study. In general, increased mortality of Ae. aegypti larvae occurred with increasing concentrations of DL-methionine at 48 h. However, larval DL-methionine LC50 values were not different between water sources. This study has shown that DL-methionine can be added to various water sources as a possible biorational larvicide when applied to natural water sources such as ponds or water-holding containers that often are preferred larval developmental sites for a variety of mosquito disease vectors.

Methionine as a safe and effective novel biorational mosquito larvicide.

Mosquito larvicides provide a source-reduction strategy to diminish adult females that bite and potentially spread pathogens. Demands are mounting for new and innovative effective biorational larvicides, due to the development of resistance to some currently utilized mosquito larvicides, undesirable non-target effects, and US Environmental Protection Agency (EPA) restrictions. Methionine is a human nutrient essential amino acid that unexpectedly has been shown to be a valuable safe pest management tool against select insect pests that possess alkaline gut physiology. The present study evaluated larvicidal toxicity of methionine in several pestiferous mosquito (Diptera: Culicidae) genera. Concentration-dependent DL-methionine kinetics assays of survival and pupation were conducted in larvae of Aedes albopictus Skuse, Anopheles quadrimaculatus Say, and Culex tarsalis Coquillett in glass jars. High concentrations of DL-methionine yielded 100% mortality for all test species and prevented pupation at a rate equivalent to Bacillus thuringiensis israelensis (Bti) treatments. Concentration kinetics indicated that An. quadrimaculatus was 10-fold more sensitive to DL-methionine than Ae. albopictus and Cx. tarsalis. EPA regulations currently exempt methionine in pesticide formulations applied to agricultural crops. This study demonstrates that methionine is a highly effective mosquito larvicide that can provide a beneficial new biorational, environmentally sustainable tool to control pestiferous mosquitoes. © 2018 Society of Chemical Industry.

Striking diflubenzuron resistance in Culex pipiens, the prime vector of West Nile Virus

Culex pipiens mosquitoes cause severe nuisance and transmit human diseases including West Nile. Vector control by insecticides is the main tool to prevent these diseases and diflubenzuron is one of the most effective mosquito larvicides used in many places. Here, high levels of resistance were identified in Cx. pipiens from Italy, with a Resistance Ratio of 128 fold. The phenotype was associated with mutations at amino acid I1043 (I1043M and I1043L) of the Chitin synthase gene, which showed significantly higher frequency in bioassay survivors. Both mutations have been introduced in the Drosophila melanogaster chitin synthase gene using the genome editing method CRISPR/Cas9 and validated to confer significant levels of resistance, although at different levels. The I→M mutation results in a Resistance Ratio >2,900 fold and the I→L mutation >20 fold. Two PCR based diagnostics were developed for monitoring of the resistant mutations in field populations. The findings are of major concern for public health given the importance of diflubenzuron in mosquito control in many places, the intensity of the resistance phenotype and the limited availability of alternative larvicides.

Eco-friendly fabrication of Ag nanostructures using the seed extract of Pedalium murex, an ancient Indian medicinal plant: Histopathological effects on the Zika virus vector Aedes aegypti and inhibition of biofilm-forming pathogenic bacteria

The control of Zika virus mosquito vectors and well as the development of drugs in the fight against biofilm-forming microbial pathogens, are timely and important challenges in current bionanoscience. Here we focused on the eco-friendly fabrication of Ag nanostructures using the seed extract of Pedalium murex, an ancient Indian medicinal plant. Initial confirmation of Ag nanoparticles (AgNPs) production was showed by a color change from transparent to dark brown. The UV–Visible spectrum (476nm), X-ray diffraction peaks (101, 200, 220 and 311) and Fourier transform infrared spectroscopy shed light on the production of green-capped AgNPs. Morphological structure analysis using HR-TEM showed that the AgNPs were mostly hexagonal in shape with rough edges, and a size of 20–30nm. The larvicidal potential of P. murex seed extract and AgNPs fabricated using the P. murex seed extract (Pm-AgNPs) was tested on fourth instar mosquito larvae of the Zika virus vector Aedes aegypti. Maximum efficacy was achieved by Pm–AgNPs against Ae. aegypti after 24h (LC50 34.88; LC90 64.56mg/ml), if compared to the P. murex seed extract. Histopathological analyses showed severe damages to the hindgut and larval muscles in NPs-treated Ae. aegypti larvae. The sub-MIC concentrations of Pm-AgNPs exhibited significant anti-biofilm activity against Gram positive (Enterococcus faecalis, Staphylococcus aureus) and Gram negative (Shigella sonnei, Pseudomonas aeruginosa) bacterial pathogens, as showed by EPS and MTP assays. Light and CLSM microscopic studies highlighted a significant impact of P. murex seed extract and Pm–synthesized AgNPs on the surface topography and architecture of bacterial biofilm, both in Gram positive and Gram negative species. Overall, results reported here contribute to the development of reliable large-scale protocols for the green fabrication of effective mosquito larvicides and biofilm inhibitors.

Toxicity of ar-curcumene and epi-β-bisabolol from Hedychium larsenii (Zingiberaceae) essential oil on malaria, chikungunya and St. Louis encephalitis mosquito vectors

Mosquitoes act as vectors of key pathogens and parasites. Plant essential oils have been recognized as important sources of biopesticides, which do not induce resistance and have limited toxic effects on human health and non-target organisms. In this research, we evaluated the larvicidal and oviposition deterrence activity of Hedychium larsenii essential oil (EO) and its major compounds ar-curcumene and epi-β-bisabolol. Both molecules showed high toxicity against early third instars of Anopheles stephensi (LC50=10.45 and 14.68µg/ml), Aedes aegypti (LC50=11.24 and 15.83µg/ml) and Culex quinquefasciatus (LC50=12.24 and 17.27µg/ml). In addition, low doses of ar-curcumene and epi-β-bisabolol were effective as oviposition deterrents against the three tested mosquito species. Notably, the acute toxicity of H. larsenii oil and its major compounds against the mosquito biocontrol agent Poecilia reticulata was low, with LC50 higher than 1500ppm. Overall, the results from this study revealed that ar-curcumene and epi-β-bisabolol from the H. larsenii oil can be considered for the development of novel and effective mosquito larvicides.

Synergized mixtures of Apiaceae essential oils and related plant-borne compounds: Larvicidal effectiveness on the filariasis vector Culex quinquefasciatus Say

The recent outbreaks of mosquito-borne diseases, such as chikungunya and Zika virus, highlighted the pivotal importance of effective mosquito control programs. Nowadays, Culicidae management is being challenging, due to the rapid development of resistance to synthetic pesticides and the spread of highly invasive mosquito vectors worldwide. This research explored the chemical composition of four Apiaceae essential oils (EOs) from Trachyspermum ammi, Smyrnium olusatrum, Pimpinella anisum and Helosciadium nodiflorum and their potential as sources of synergistic binary mixtures with high effectiveness against larvae of the filariasis vector Culex quinquefasciatus. The essential oils were all highly toxic to the larvae, showing LC50 of 17.6, 17.5, 25.9 and 20.6μlL−1, respectively. GC–MS analysis put in evidence thymol, (E)-anethole, myristicin and (Z)-β-ocimene, and isofuranodiene and germacrone as the main essential oil components, respectively. Three effective EOs were selected to prepare binary mixtures. T. ammi+P. anisum (ratio 1:2) and S. olusatrum+P. anisum (ratio 1:1) were the most toxic larvicidal blends, showing LC50 of 15.2 and 16.9, μlL−1, respectively. LT50 values were 45 and 30min, respectively. Notably, short time exposure to both binary mixtures strongly reduced emergence rates, fertility and natality of C. quinquefasciatus that survived after the treatment at the larval stage. Larvicidal assays assessing the acute toxicity of EO main constituents, i.e. germacrone, isofuranodiene and (E)-anethole, were carried out. LC50 were 18.6mgL−1, 33.7mgL−1 and 24.8μlL−1. Overall, our results pointed out the promising potential of these EOs to develop cheap and effective mosquito larvicides, as well as the importance to consider the synergistic effects among the tested botanicals during the design of novel mosquito larvicides.

Trypsin-modulating oostatic factor (TMOF) decreased the survival, growth and digestion enzymes of Macrobrachium rosenbergii.

Trypsin-modulating oostatic factor (TMOF) is an effective mosquito larvicide, but information on its potential toxicity to non-target organisms is limited. To investigate this, triplicate groups of 10 Macrobrachium rosenbergii were exposed to 0, 10, 50 or 100 mg/L nominal TMOF concentrations for 12 days. Tail moisture, crude protein, and hepatopancreatic glycogen/histopathology were unaffected, but increasing TMOF linearly decreased survival and growth. TMOF at the lowest concentration employed significantly decreased trypsin and chymotrypsin activities.

Laboratory evaluation of ethyl acetate and chloroform: methanol (1:1 v/v) extract of Swietenia mahagoni leaf against Japanese Encephalitis vector Culex vishuni group

ObjectiveTo study the larvicidal activity of a furniture tree Swietenia mahagoni L. (S. mahagoni) against mosquito Culex Vishnui group. MethodsDifferent concentrations of crude, chloroform: methanol (1:1 v/v) and ethyl acetate solvent extracts of S. mahagoni mature leaves were treated against Cx. vishnui group larvae. ResultsFive graded concentrations (0.05%, 0.10%, 0.20%, 0.30% and 0.40%) of crude extract of mature leaves and five graded concentrations (10 ppm, 20 ppm, 30 ppm, 40 ppm and 50 ppm) of chloroform: methanol (1:1 v/v) and ethyl acetate solvent extracts showed significant (P<0.05) larval mortalities. LC50, LC90 values were calculated at 24 h, 48 h and 72 h of exposures. Adult Cx. vishnui group mosquitoes exposed to burning coils prepared from S. mahagoni mature leaves showed smoke repellency and toxicity up to 4 h. ConclusionsThis study was a pioneer attempt to establish S. mahagoni as an effective mosquito larvicide.

Development of Emulsified Concentrate (EC) formulation of Mentha piperita oil for control of mosquito larvae

Background Malaria is a leading cause of morbidity and mortality with an estimated 2.2 billion reported cases and 0.7 million annual deaths [1]. Continued research for malaria control although has resulted in significant reduction in malaria mortality rate, investigative measures are needed to address the escalating cost and threat of pesticide resistance. In this direction, biological control agent such as essential oil presents a good alternative [2-4]. However, the commercial applicability of essential oils for mosquitoes control is plagued by their slow action, variable efficacy and lack of suitable/user friendly end product [5]. Thus, in the present study Emulsified concentrate (EC) formulation of Mentha piperita oil, an effective mosquito larvicide [2,3], was prepared and characterized.

Spinosad: a biorational mosquito larvicide for use in car tires in southern Mexico

BackgroundCar tires are important habitats for mosquito development because of the high density populations they can harbor and their presence in urban settings. Water in experimental tires was treated with one of three insecticides or an untreated control. Aquatic invertebrates were sampled at weekly intervals. Eggs, larval and pupal samples were laboratory-reared to estimate seasonal fluctuations in Aedes aegypti and Ae. albopictus abundance.ResultsSpinosad treatments at 1 or 5 ppm (mg a.i./liter) provided 6–8 weeks of effective control of Ae. aegypti, Ae. albopictus, Culex quinquefasiatus and Cx. coronator larvae, both in the dry season and the rainy season when mosquito populations increased markedly in southern Mexico. Spinosad continued to provide partial control of larvae for several weeks after initial recolonization of treated tires. The larvicidal performance of VectoBac 12AS (Bacillus thuringiensis var. israelensis) was relatively poor with one week of complete control of Aedes spp. larvae and no discernible control of Culex spp., whereas the duration of larvicidal activity of 1% temephos mineral-based granules was intermediate between those of VectoBac and spinosad treatments. Populations of chironomids, ostracods and Toxorhynchites theobaldi were generally reduced in spinosad and temephos treatments, but were similar in control and VectoBac treatments.ConclusionThe present study is the first to report spinosad as an effective larvicide against Cx. coronator, which is currently invading the southern United States. These results substantiate the use of spinosad as a highly effective mosquito larvicide, even in habitats such as unused car tires that can represent prolific sources of adult mosquitoes.