Evaluation of Brown and red seaweeds-extracts as a novel larvicidal agent against the deadly human diseases-vectors, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus.

Infectious diseases such as malaria, dengue, and yellow fever are predominantly transmitted by insect vectors like Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus in tropical regions like India and Africa. In this study, we assessed the larvicidal activity of commonly found seaweeds, including Padina gymnospora, P. pavonica, Gracilaria crassa, Amphiroa fragilissima, and Spatoglossum marginatum, against these mosquito vectors. Our findings indicate that extracts from P. gymnospora Ethyl Acetate (PgEA), P. pavonica Hexane (PpH), and A. fragilissima Ethyl Acetate (AfEA) displayed the highest larval mortality rates for A. stephensi, with LC50 values of 10.51, 12.43, and 6.43 µg/mL, respectively. Additionally, the PgEA extract from P. gymnospora exhibited the highest mortality rate for A. aegypti, with an LC50 of 27.0 µg/mL, while the PgH extract from the same seaweed showed the highest mortality rate for C. quinquefasciatus, with an LC50 of 9.26 µg/mL. Phytochemical analysis of the seaweed extracts revealed the presence of 71 compounds in the solvent extracts. Fourier-transform infrared spectra of the selected seaweeds indicated the presence of functional groups such as alkanes, alcohols, and phenols. Gas chromatography-mass spectrometry analysis of the seaweeds identified major compounds, including hexadecanoic acid in PgEA, tetradecene (e)- in PpEA, octadecanoic acid in GcEA, and 7-hexadecene, (z)-, and trans-7-pentadecene in SmEA.

Bioactivity of select essential oil constituents against life stages of Anopheles arabiensis (Diptera: Culicidae).

Malaria is transmitted by infected female Anopheles mosquitoes, and An. arabiensis is a main malaria vector in arid African countries. Like other anophelines, its life cycle comprises of three aquatic stages; egg, larva, and pupa, followed by a free flying adult stage. Current vector control interventions using synthetic insecticides target these stages using adulticides or less commonly, larvicides. With escalating insecticide resistance against almost all conventional insecticides, identification of agents that simultaneously act at multiple stages of Anopheles life cycle presents a cost-effective opportunity. A further cost-effective approach would be the discovery of such insecticides from natural origin. Interestingly, essential oils present as potential sources of cost-effective and eco-friendly bioinsecticides. This study aimed to identify essential oil constituents (EOCs) with potential toxic effects against multiple stages of An. arabiensis life cycle. Five EOCs were assessed for inhibition of Anopheles egg hatching and ability to kill larvae, pupae and adult mosquitoes of An. arabiensis species. One of these EOCs, namely methyleugenol, exhibited potent Anopheles egg hatchability inhibition with an IC50 value of 0.51 ± 0.03 µM compared to propoxur (IC50: 5.13 ± 0.62 µM). Structure-activity relationship study revealed that methyleugenol and propoxur share a 1,2-dimethoxybenze moiety that may be responsible for the observed egg-hatchability inhibition. On the other hand, all five EOCs exhibited potent larvicidal activity with LC50 values less than 5 µM, with four of them; cis-nerolidol, trans-nerolidol, (-)-α-bisabolol, and farnesol, also possessing potent pupicidal effects (LC50 < 5 µM). Finally, all EOCs showed only moderate lethality against adult mosquitoes. This study reports for the first time, methyleugenol, (-)-α-bisabolol and farnesol as potent bioinsecticides against early life stages of An. arabiensis. This synchronized activity against Anopheles aquatic stages shows a prospect to integrate EOCs into existing adulticide-based vector control interventions.

Temephos, an organophosphate larvicide for residential use: a review of its toxicity.

Temephos (O,O,O',O'-tetramethyl O,O'-thiodi-p-phenylene bis(phosphorothioate)) is a larvicide belonging to the family of organophosphate pesticides used for the control of different vectors of diseases, such as dengue, Zika, chikungunya, and dracunculiasis. The aim of this review was to discuss the available published information about temephos toxicokinetics and toxicity in mammals. Temephos is quickly absorbed in the gastrointestinal tract, distributed to all organs, and then it accumulates mainly in adipose tissue. It is metabolized by S-oxidation, oxidative desulfuration, and hydrolysis reactions, with the possible participation of cytochrome P450 (CYP). Temephos is mainly eliminated by feces, whereas some of its metabolites are eliminated by urine. The World Health Organization classifies it as class III: slightly dangerous with a NOAEL (no-observed adverse effect level) of 2.3 mg/kg/day for up to 90 days in rats, based on brain acetylcholinesterase (AChE) inhibition. A LOAEL (lowest observable adverse effect level) of 100 mg/kg/day for up to 44 days in rats was proposed based on cholinergic symptoms. However, some studies have shown that temephos causes toxic effects in mammals. The inhibition of the enzyme acetylcholinesterase (AChE) is one of its main demonstrated effects; however, this larvicide has also shown genotoxic effects and some adverse effects on male reproduction and fertility, as well as liver damage, even at low doses. We performed an extensive review through several databases of the literature about temephos toxicokinetics, and we recommend to revisit current assessment of temephos with the new available data.

Life-history attributes of juvenile Anopheles gambiae s.s. in central Uganda; implications for malaria control interventions.

Malaria is among the leading causes of death in Uganda, and Anopheles gambiae sensu stricto (s.s.) is the predominant vector. Although current vector control interventions have greatly reduced the malaria burden, the disease persists. New interventions are needed in order to eradicate them. Evaluation of new tools will require the availability of well-characterized test vector populations. Juvenile An. gambiae s.s. from Kibbuye and Kayonjo-derived populations were characterized under semi-field and laboratory conditions, given that various vector traits, including abundance and fitness are dependent on development profiles at this life stage. Ten replicates comprising 30 first instar larvae each were profiled for various life-history attributes (egg hatching, larval development time, larval survivorship, pupal weight and pupation rate). All parameters were similar for the two sites under laboratory conditions. However, the similarities or differences between field and laboratory development were parameter-specific. Whereas, larval survivorship and pupal weight were similar across seasons and laboratory in colonies from both sites, in the semi-field settings, pupation rate and larval survivorship differed between seasons in both sites. In addition, the average larval development time during the wet season was longer than that of the laboratory for both sites. Availability of mirror field sites is important for future tool evaluations.

Sublethal effects of oregano essential oil and its major compound carvacrol on biological parameters of Aedes albopictus (Diptera: Culicidae).

Mosquito management programs rely basically on the use of conventional synthetic larvicides. However, frequent applications and misuse of some synthetic insecticides have led to problems related to mosquito resistance development, harmful effects on human health and unacceptable environmental effects on non-target organisms. Recently, a growing number of phytochemicals has been tested as more eco-friendly larvicides against various mosquito species, exerting high efficacy with multiple modes of action. In the laboratory, we investigated for the first time the sublethal effects of oregano oil and its major compound carvacrol, against Aedes albopictus (Asian tiger mosquito), a mosquito of great medical importance. We determined the effects of short term (24h) exposure of 3rd- 4th larvae to LC50 concentrations on survival and development of survived larvae until adulthood, as well as on fecundity, fertility, longevity and wing length of emerged adults. Only half of 24h survived larvae from oregano oil and carvacrol treatment finally reached adulthood. Abnormal shapes of dead larvae and pupae, and failed adult emergence were also observed, indicating a potential growth inhibitory activity of the tested materials. No particular effects from exposure to larvicidal LC50 concentrations were recorded on life cycle parameters of successfully emerged adults. These findings suggest the tested oregano oil and carvacrol as sufficiently effective larvicides against Ae. albopictus at lower than the acutely toxic concentrations, promoting a more eco-friendly and less costly profile for these biopesticides.

Comparison of novaluron, pyriproxyfen, spinosad and temephos as larvicides against Aedes aegypti in Chiapas, Mexico.

OBJECTIVE: To compare the efficacy of three modern larvicides with the organophosphate temephos for control of Aedes aegypti in water tanks in Chiapas. MATERIALS AND METHODS: Trials were performed to compare the efficacy of pyriproxyfen, novaluron, two formulations of spinosad (granules and tablets) and temephos in oviposition traps and domestic water tanks. RESULTS: Pyriproxyfen and temephos provided 2-3 weeks of complete control of larvae in oviposition traps, whereas spinosad granules and novaluron provided 7-12 weeks of control. Treatment of water tanks resulted in a significant reduction in oviposition by Ae. aegypti in houses (p<0.001). Higher numbers of larvae were present in temephos and pyriproxyfen-treated water tanks compared to novaluron and spinosad tablet treatments during most of the study. CONCLUSIONS: Spinosad formulations and novaluron were effective larvicides in this region. The poor performance of temephos may be indicative of reduced susceptibility in Ae. aegypti populations in Chiapas.

OBJETIVO: Comparar la eficacia de tres larvicidas modernos para el control de Aedes aegypti en tanques de agua doméstica en Chiapas. MATERIAL Y MÉTODOS: Se comparó la eficacia de piriproxifeno, novalurón, dos formulaciones de spinosad (gránulos y tabletas) y temefos en ovitrampas y tanques domésticos de agua. RESULTADOS: El piriproxifeno y el temefos proporcionaron de 2 a 3 semanas de control de larvas en ovitrampas, mientras que los gránulos de spinosad y novaluron proporcionaron de 7 a12 semanas. Los tanques de agua tratados produjeron una reducción significativa en la oviposición por Ae. aegypti en las casas (p<0.001). Se encontró gran cantidad de larvas en los tanques tratados con temefos y piriproxifeno en comparación con los tratados con novaluron y tabletas de spinosad durante la mayor parte del estudio. CONCLUSIONES: Las formulaciones de spinosad en tabletas y novaluron fueron larvicidas efectivos en esta región. El bajo desempeño de temefos puede indicar una susceptibilidad reducida en poblaciones de Ae. aegypti en Chiapas.

Chemical composition and assessment of larvicidal and repellent capacity of 14 Lamiaceae essential oils against Aedes albopictus.

In the current laboratory study, 14 essential oils (EOs) derived from 12 Lamiaceae plant species and their major components were screened for their larvicidal and repellent properties against Aedes albopictus, an invasive mosquito species of great medical importance. The results of toxicity bioassays revealed that the EOs from Thymus vulgaris, Ocimum basilicum, Origanum dictamnus, Origanum majorana, and Origanum vulgare, as well as their major components (terpenes), namely thymol, carvacrol, p-cymene, and γ-terpinene exerted the highest larvicidal effect. Essential oils from Mellisa officinalis, Origanum dictamus, Mentha spicata (chem. piperitenone epoxide), Origanum majorana, and Satureja thymbra were the most potent repellents, with the last two assigned as the best ones. Among the terpenes tested, piperitenone epoxide, carvacrol, thymol, and piperitenone provided the highest level of protection against Ae. albopictus adults. Chemical analysis revealed the presence of a high number of terpenes in the EOs, while in most cases, the biological action of the tested EOs and their major components was in consistency. The most effective EOs and terpenes that were identified through the current laboratory bioassays could be used as alternative agents to control larvae and repel adults of Ae. albopictus.

Cost of microbial larviciding for malaria control in rural Tanzania.

OBJECTIVE: Microbial larviciding may be a potential supplement to conventional malaria vector control measures, but scant information on its relative implementation costs and effectiveness, especially in rural areas, is an impediment to expanding its uptake. We perform a costing analysis of a seasonal microbial larviciding programme in rural Tanzania. METHODS: We evaluated the financial and economic costs from the perspective of the public provider of a 3-month, community-based larviciding intervention implemented in twelve villages in the Mvomero District of Tanzania in 2012-2013. Cost data were collected from financial reports and invoices and through discussion with programme administrators. Sensitivity analysis explored the robustness of our results to varying key parameters. RESULTS: Over the 2-year study period, approximately 6873 breeding sites were treated with larvicide. The average annual economic costs of the larviciding intervention in rural Tanzania are estimated at 2014 US$ 1.44 per person protected per year (pppy), US$ 6.18 per household and US$ 4481.88 per village, with the larvicide and staffing accounting for 14% and 58% of total costs, respectively. CONCLUSIONS: We found the costs pppy of implementing a seasonal larviciding programme in rural Tanzania to be comparable to the costs of other larviciding programmes in urban Tanzania and rural Kenya. Further research should evaluate the cost-effectiveness of larviciding relative to, and in combination with, other vector control strategies in rural settings.

Field effectiveness of microbial larvicides on mosquito larvae in malaria areas of Botswana and Zimbabwe.

BACKGROUND: The successful control of malaria vectors requires the control of both the larval and adult stages. The adult control methods through indoor residual spraying (IRS) and use of long-lasting insecticidal nets (LLINs) continue to be widely used with some high measure of success. Larval control methods are also being used by a number of National Malaria Control Programmes (NMCPs) with limited understanding of its contribution. Larval control might be needed in some areas to move from malaria control to elimination. This experimental study was conducted to assess the field effectiveness of winter larviciding on the larval stages of the mosquito in Botswana and Zimbabwe. METHODS: Two villages were selected in each of the two countries, one as an intervention and the other as the control. Water bodies in the intervention villages were treated using the commercial product VectoBac® WG (Valent BioSciences Corporation, IL, USA) containing the active ingredient Bacillus thuringiensis var. israelensis (Bti), a WHO recommended bio-larvicide, applied at a rate of 300 g per hectare. Random-effects Poisson regression was employed during data analysis to compare intervention with control sites with respect to larval counts. RESULTS: The average marginal effect of larviciding on the mosquito larvae taking interaction with time (period) into account, was -1.94 (95% CI -2.42 to -1.46) with incidence rate ratio of 0.14, thus an 86% larval reduction attributable to the intervention for both countries combined. There was a 92% and 65% effect for Botswana and Zimbabwe respectively. The effect on the early larval and late stages was 77% (P < 0.001) and 91% (P < 0.001), respectively. Overall, intervention larval sampling points had five more larvae than the control at baseline and 26 less after 16 weeks. The effect on the different species also showed similar trends. DISCUSSION/CONCLUSION: Larval control using Bti showed a high effect on the population of the mosquito larvae. The reduction of the early and late larval stages can lead to reduced adult mosquito emergence and low adult mosquito densities. Larviciding can be used to control mosquito vector population by suppressing the larval stages thereby reducing adult emergence and malaria risk.

Green synthesis and characterization of silver nanoparticles fabricated using Anisomeles indica: Mosquitocidal potential against malaria, dengue and Japanese encephalitis vectors.

Mosquitoes (Diptera: Culicidae) represent a key threat for millions of people worldwide, since they act as vectors for devastating parasites and pathogens. In this scenario, eco-friendly control tools against mosquito vectors are a priority. Green synthesis of silver nanoparticles (AgNP) using a cheap, aqueous leaf extract of Anisomeles indica by reduction of Ag(+) ions from silver nitrate solution has been investigated. Bio-reduced AgNP were characterized by UV-visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX) and X-ray diffraction analysis (XRD). The acute toxicity of A. indica leaf extract and biosynthesized AgNP was evaluated against larvae of the malaria vector Anopheles subpictus, the dengue vector Aedes albopictus and the Japanese encephalitis vector Culex tritaeniorhynchus. Both the A. indica leaf extract and AgNP showed dose dependent larvicidal effect against all tested mosquito species. Compared to the leaf aqueous extract, biosynthesized AgNP showed higher toxicity against An. subpictus, Ae. albopictus, and Cx. tritaeniorhynchus with LC50 values of 31.56, 35.21 and 38.08 µg/mL, respectively. Overall, this study firstly shed light on the mosquitocidal potential of A. indica, a potential bioresource for rapid, cheap and effective AgNP synthesis.

Toxicity of 25 synthetic insecticides to the field population of Culex quinquefasciatus Say.

The Culex quinquefaciatus Say, commonly known as the southern house mosquito, is well known for biting nuisance and vectoring of some fatal diseases. Synthetic chemicals have been relied upon as the major control measure to control mosquitoes. Therefore, we have evaluated 21 insecticides belonging to different chemical classes for their toxicity to C. quinquefaciatus females. Chlorfenapyr was the most toxic adulticide among all the tested insecticides. Among pyrethroids, deltamethrin was the least toxic adulticide, and all other have same toxicity. In case of organophosphates, the chlorpyrifos was the most toxic insecticide. Neonicotinoids such as acetamiprid, nitenpyram, and clothianidin have similar toxicity based on overlapping of 95 % confidence intervals (CI) and were more toxic when compared with the imidacloprid. The spinetoram was more toxic as compared with the spinosad (based on non-overlapping 95 % Cl). In case of ketoenoles, spirotetrament was more toxic as compared with the spiromesifen. Emamectin benzoate was the most toxic insecticide when compared with fipronil and indoxacarb. We also have tested four insect growth regulators (IGRS) including lufenuron, methoxyfenozide, pyriproxyfen, and cyromazine as larvicides. The lufenuron and pyriproxyfen have similar toxicity based upon their overlapping 95 % CI and were more toxic as compared with the methoxyfenozide and cyromazine. The methoxyfenozide was the moderately toxic among all the tested IGRS, and cyromazine was the least toxic among all the tested IGRS. These results will prove helpful in effectuating an effective integrated vector management program for C. quinquefaciatus.

Eugenol, α-pinene and ß-caryophyllene from Plectranthus barbatus essential oil as eco-friendly larvicides against malaria, dengue and Japanese encephalitis mosquito vectors.

Mosquito-borne diseases represent a deadly threat for millions of people worldwide. Eco-friendly mosquitocides are a priority. In Ayurvedic medicine, Plectranthus species have been used to treat heart disease, convulsions, spasmodic pain and painful urination. In this research, we evaluated the acute toxicity of essential oil from Plectranthus barbatus and its major constituents, against larvae of the malaria vector Anopheles subpictus, the dengue vector Aedes albopictus and the Japanese encephalitis vector Culex tritaeniorhynchus. The chemical composition of P. barbatus essential oil was analyzed by gas chromatography-mass spectroscopy. Nineteen components were identified. Major constituents were eugenol (31.12%), α-pinene (19.38%) and ß-caryophyllene (18.42%). Acute toxicity against early third-instar larvae of An. subpictus, Ae. albopictus and Cx. tritaeniorhynchus was investigated. The essential oil had a significant toxic effect against larvae of An. subpictus, Ae. albopictus and Cx. tritaeniorhynchus, with 50% lethal concentration (LC50) values of 84.20, 87.25 and 94.34 µg/ml and 90% lethal concentration (LC90) values of 165.25, 170.56 and 179.58 µg/ml, respectively. Concerning major constituents, eugenol, α-pinene and ß-caryophyllene appeared to be most effective against An. subpictus (LC50 = 25.45, 32.09 and 41.66 µg/ml, respectively), followed by Ae. albopictus (LC50 = 28.14, 34.09 and 44.77 µg/ml, respectively) and Cx. tritaeniorhynchus (LC50 = 30.80, 36.75 and 48.17 µg/ml, respectively). Overall, the chance to use metabolites from P. barbatus essential oil against mosquito vectors seems promising, since they are effective at low doses and could be an advantageous alternative to build newer and safer mosquito control tools.

Larvicidal activity of diterpenes from Xylopia langsdorfiana St. Hilaire & Tulasne (Annonaceae) against Aedes aegypti linn. (diptera: culicidae).

Mosquitoes of the Aedes genus are responsible for transmitting many vector-borne viral diseases worldwide. Hundreds of thousands of people die annually from vector-borne diseases, including West Nile fever, dengue, tick-borne diseases, yellow fever, chikungunya, Rift Valley fever, and Zika. Billions of people are at the risk of infection on all continents, which is a cause of international concern. Therefore, new vector-control methods are essential for mitigating these illnesses. The bioactive hydrocarbons isolated from Xylopia langsdorfiana St. Hilaire & Tulasne are trachylobanes, a rare class of diterpenes found in the n-hexane fraction of the stem and leaf ethanolic extracts. These were tested against Ae. aegypti fourth-instar larvae over 48 h of exposure, with LC50 values ranging from 19.84 to 72.9 µg/mL, comparable to that of the positive control. The findings highlight the potential of Xylopia langsdorfiana St. Hilaire & Tulasne metabolites for controlling the main vectors of arthropod-borne viruses.

Efficacy of maturase K and rpL20 protein extracted from C. procera leaves on Anophelesstephensi.

The present work is carried out to protein isolation, purification, and characterization from leaves, stem, and seed of C. procera and to evaluate the larvicidal potential on Anopheles stephensi. The whole protein was isolated using protein extraction buffer and precipitated by ammonium sulphate and larvicidal active protein was purified by the column chromatography. The homogeneity of larvicidal protein was confirmed by the SDS-PAGE. The identification of protein was done by the HPLC and LC-MS/ESI-MS. The crude protein from leaves showed 100% mortality of 3rd instar larvae of An. stephensi at the concentration of 5.5 mg/ml after 24 h of exposure. The crude protein from stem showed 25% mortality and no mortality observed was observed in seed protein. The leaves crude protein was further purified by ion exchange chromatography and eluted fractions were tested for larvicidal potential. The purified single protein fractions L2 and L3 from C. procera leaves showed 100% mortality at concentration of 0.06 mg/ml. The homogeneity of purified protein was confirmed by SDS-PAGE and two bands of 26 kDa and 15 kDa protein were observed. The peptide sequence "R.SQMLENSFLIENVMKR.L" was identified in the trypsin digested homogenous protein fraction L2 and "R.DRGSQKR.N" peptide sequence in L3 fraction by LC-MS/ESI-MS. The CprL2 peptide showed the sequence similarity with the protein maturase K and CprL3 peptide showed the sequence similarity with ribosomal protein L20 of C. procera. The conserved functional domain was also identified in both the CprL2 and CprL3 peptide. The identified proteins showed strong larvicidal efficacy at very low concentration. The identified proteins are novel and natural larvicidal agents against An. stephensi and hence can be used to control the malaria.

Comparative analysis of the larvicidal activity of temephos (EC50) and novaluaron (EC10) to control Anopheles stephensi in Sri Lanka.

BACKGROUND: Anopheles stephensi was first recorded in the coastal area of Mannar District, Sri Lanka, in December 2016. Since then, this vector has been isolated from other districts in the Northern and Eastern Provinces of Sri Lanka. Chemical control is the main arm of vector control that can be used to reduce the vector densities within a short period. Thus, the present study aimed at evaluating the efficacy of using selected insecticides for the control of An. stephensi larvae. METHOD: The third and fourth instar larval stages of An. stephensi (F2 generation) of field mosquitoes that were caught using cattle baited net trap collections from Columbuthurai, Kurunagar, and Navanthurai areas in Jaffna District, Sri Lanka, were obtained from the laboratory colony established at Jaffna. Batches of 100 larvae were taken for experiments and introduced separately to a concentration series of temephos and novaluron (0.04-400 ppm). A control test was also performed at each setup without introducing insecticides. The mortality rates of An. stephensi larvae exposed to different concentrations of larvicides were recorded at 1, 24 and 48-h intervals. The experiment was replicated five times at individual concentrations for each selected chemical. Data were analyzed using the General Linear Model (GLM) and Probit analysis. RESULTS: The highest mortality rate (100%) at a 1-h exposure period was observed from temephos at >100 ppm. The mortality rates varied significantly for different concentrations and larvicides (p < 0.05). At 24-h of the exposure period, the 100% mortality of An. stephensi larvae were observed from both temephos and novaluron even at 0.04 ppm. CONCLUSION: Both temephos and novaluron reported 100% mortality rates in An. stephensi larvae at 1-h and 24-h exposure periods. Based on the findings, temephos and novaluron can be recommended as effective larvicides for chemical-based control of An. stephensi in Jaffna, Sri Lanka. Further, it is recommended to conduct a field-based study, where habitat types and water quality are highly heterogeneous and may affect the residual activity.

Residual efficacy of selected larvicides against Culex pipiens pipiens (Diptera: Culicidae) under laboratory and semi-field conditions.

Mosquitoes are a threat worldwide since they are vectors of important pathogens and parasites such as malaria, dengue, yellow fever, and West Nile. The residual toxicity of several commercial mosquito larvicides was evaluated for the control of Culex pipiens pipiens under controlled laboratory and semi-field conditions during late spring and summer of 2013. The evaluation included six different active ingredient formulations, i.e., diflubenzuron Du-Dim), Bacillus thuringiensis var. israelensis (Bti) (Vectobac), spinosad (Mozkill), S-methoprene (Biopren), temephos (Abate), and polydimethylsiloxane (PDMS) (Aquatain), that are currently registered of and had been registered in the past for mosquito control. Under controlled laboratory conditions, the residual activity ranged from 1 week (S-methoprene) up to 2 months (spinosad, PDMS). Exposure of larvicides under semi-field conditions resulted in noticeable differences regarding their efficacy as compared to the laboratory bioassays. Exposure of S-methoprene, Bti, and spinosad, for up to 3 days, resulted in similar adult emergence to the controls. On the other hand, the residual efficacy of diflubenzuron, temephos, and PDMS ranged from 14 to 28 days, depending on the season of exposure. Longevity and fecundity of adults that had emerged from surviving larvae, in most of the cases tested, did not differ significantly from that of the controls. The results of the present study demonstrate the necessity of both field and laboratory studies to draw safe conclusions regarding the efficacy of larvicides against mosquitoes and the selection of the proper formulation for each application scenario. In addition, defining the seasonal variation in the residual toxicity of the tested formulations could be useful for improving mosquitos' management programs.

Design, synthesis, characterization and insecticidal screening of novel anthranilic diamides comprising acyl thiourea substructure.

BACKGROUND: Mosquito-borne pathogens constitute a major health problem worldwide. The extermination of the mosquito remains a significant issue in public health. Chemical insecticides have been used to control mosquitoes for decades. However, resistance has become a limiting factor for their control. The anthranilic diamide insecticides possess excellent insecticidal activities against Lepidoptera and its resistant strains by draining internal calcium stores on activating insect ryanodine receptors. However, the reports on the effect on mosquitoes are scarce and hence a series of novel anthranilic diamides comprising acyl thiourea substructure were synthesized and their insecticidal activities against three vector mosquito larvae namely, Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi were evaluated as per WHO protocol. Also investigated the morphological observations of treated larvae. RESULTS: Novel anthranilic diamides containing an acyl thiourea substructure were synthesized and structures were established by 1 H nuclear magnetic resonance (NMR), 13 C NMR, Fourier transform infrared (FTIR) and high-resolution mass spectrometry (HR-MS). Mosquito larvicidal activity of the title compounds 6-a-s revealed that compound 6-l exhibited marked larvicidal activities against C. quinquefasciatus and A. aegypti 3rd instar larvae with median lethal concentrations (LC50 ) values of 0.0044 mm and 0.0070 mm, respectively, for 48 hours of treatment. Compound 6-g exhibited larvicidal activity against An. stephensi with LC50 value of 0.0085 mm. Peculiar morphological alterations in the body of the treated larvae leading to death were observed on microscopic examination. CONCLUSION: Novel anthranilic diamides containing an acyl thiourea substructure were designed, synthesized and characterized. Their bioassay results demonstrated significant mosquito larvicidal activity with striking morphological alterations in the body, which should ensure forthcoming designs of highly active diamide derivatives as mosquito larvicides. © 2022 Society of Chemical Industry.

Evaluating the Sublethal Effects of Origanum vulgare Essential Oil and Carvacrol on the Biological Characteristics of Culex pipiens biotype molestus (Diptera: Culicidae).

Culex pipiens is a mosquito species complex spread worldwide that poses a serious threat to human health as the primary vector of West Nile virus. Its control is mainly based on larvicidal applications with synthetic insecticides on mosquito breeding sites. However, the excessive use of synthetic larvicides may provoke mosquito resistance issues and negative side effects to the aquatic environment and human health. Plant-derived essential oils, including those from the Lamiaceae family, can be eco-friendly alternative larvicidal agents causing acute larval toxicity and/or growth inhibitory effects on the developmental stages of mosquitoes through different modes of action. In the current laboratory study, we evaluated the sublethal effects of carvacrol-rich oregano essential oil and pure carvacrol on Cx. pipiens biotype molestus, the autogenous member of the Cx. pipiens species complex, after the exposure of 3rd-4th instar larvae to LC50 concentrations. The short-term (24 h) larvicidal treatment with the sublethal concentrations of both tested materials exhibited an acute lethal effect on the exposed larvae as well as significant delayed mortality for surviving larvae and pupae. Larvicidal treatment with carvacrol reduced the longevity of the emerged males. In addition, the morphological abnormalities that were observed at the larval and pupal stage along with failed adult emergence indicate the potential growth inhibitory properties of the tested bioinsecticides. Our findings suggest that carvacrol and carvacrol-rich oregano oil are effective plant-based larvicides at doses lower than the acute lethal ones, thus promoting an environmentally friendly and more affordable perspective for their use against the WNV vector Cx. pipiens biotype molestus.

Culex quinquefasciatus Resistant to the Binary Toxin from Lysinibacillus sphaericus Displays a Consistent Downregulation of Pantetheinase Transcripts.

Culex quinquefasciatus resistance to the binary (Bin) toxin, the major larvicidal component from Lysinibacillus sphaericus, is associated with mutations in the cqm1 gene, encoding the Bin-toxin receptor. Downregulation of the cqm1 transcript was found in the transcriptome of larvae resistant to the L. sphaericus IAB59 strain, which produces both the Bin toxin and a second binary toxin, Cry48Aa/Cry49Aa. Here, we investigated the transcription profiles of two other mosquito colonies having Bin resistance only. These confirmed the cqm1 downregulation and identified transcripts encoding the enzyme pantetheinase as the most downregulated mRNAs in both resistant colonies. Further quantification of these transcripts reinforced their strong downregulation in Bin-resistant larvae. Multiple genes were found encoding this enzyme in Cx. quinquefasciatus and a recombinant pantetheinase was then expressed in Escherichia coli and Sf9 cells, with its presence assessed in the midgut brush border membrane of susceptible larvae. The pantetheinase was expressed as a ~70 kDa protein, potentially membrane-bound, which does not seem to be significantly targeted by glycosylation. This is the first pantetheinase characterization in mosquitoes, and its remarkable downregulation might reflect features impacted by co-selection with the Bin-resistant phenotype or potential roles in the Bin-toxin mode of action that deserve to be investigated.

Insecticidal effectiveness of naphthalene and its combination with kerosene against the emergence of Aedes aegypti in Ika North East, LGA, Delta State, Nigeria.

Despite the substantial progress achieved in the search of nonchemical alternatives to insecticidal larviciding on mosquitoes, more work is still required to unravel the potency of viable substances in order to attend to several pest and disease problems. Insecticidal effectiveness of naphthalene and its combination with kerosene against the emergence of Ae. aegypti in Ika North East, LGA, Delta State, Nigeria was assessed. Immature stages of Ae. aegypti were collected and left to acclimatize for 6 h in standard laboratory conditions. Naphthalene measured in 2 g and its combinations with kerosene in 50:50 were emptied in 400 ml, 200 ml and 100 ml of water which resulted in 0.005%, 0.01% and 0.02% concentrations respectively. Water alone served as control for the experiment. Twenty third instar larvae and pupae were sorted into containers before exposure to treatments. Experiment was done in triplicates and observed for 10, 15, 20, 30, 40, 50, 60, and 80 min coinciding with WHO protocol for Aedes exposure. Mortality was highest in larvae exposed to 0.02% kerosene and naphthalene, and was also high in 0.02% naphthalene. Lowest mortality was recorded in pupae exposed to 0.005% of naphthalene. Significant differences in toxicity was recorded (p < 0.05). Mortality increased with time in larvae and pupae. Highest mortality in pupae and larvae was recorded in 0.02% kerosene and naphthalene mixture at 80 min post exposure time respectively. LC50 and LC95 of naphthalene exposed to Aedes larvae and pupae was between 0.002 and 0.018% and 0.021-0.051% respectively. Similarly, for naphthalene with kerosene was between 0.002 and 0.007%, and 0.015-0.035%. Pupae exposed to 0.005% naphthalene had more adult emergence than in others and the differences were significant (p < 0.05). Field trial is required with optimum concentrations.